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American Airlines Flight 77

American Airlines Flight 77 was a scheduled domestic transcontinental passenger flight from Dulles International Airport in Northern Virginia to Los Angeles International Airport in Los Angeles. The Boeing 757-200 aircraft serving the flight was hijacked by five al-Qaeda terrorists on the morning of September 11, 2001, as part of the September 11 attacks. The hijacked airliner was deliberately crashed into the Pentagon in Arlington County, Virginia, killing all 64 aboard and another 125 in the building.

Flight 77 became airborne at 08:20 ET. Thirty-one minutes after takeoff, the attackers stormed the cockpit and forced the passengers and crew to the rear of the cabin, threatening the hostages but initially sparing all of them. Lead hijacker Hani Hanjour assumed control of the aircraft after having undergone extensive flight training as part of his preparation for the attack. In the meantime, two people aboard discreetly made phone calls to family members and relayed information on the situation without the knowledge of their assailants.

Hanjour flew the airplane into the west side of the Pentagon at 09:37. Many people witnessed the impact, and news sources began reporting on the incident within minutes, but no clear footage of the crash itself is available to the public. The 757 severely damaged an area of the Pentagon and caused a large fire that took several days to extinguish. By 10:10, the damage inflicted by the plane and ignited jet fuel led to a localized collapse of the Pentagon's western flank, followed forty minutes later by another five stories of the structure. Flight 77 was the third of four passenger jets to be commandeered by terrorists that morning, and the last to reach a target intended by al-Qaeda. The hijacking was to be coordinated with that of United Airlines Flight 93, which was flown in the direction of Washington, D.C., the U.S. capital. The terrorists on Flight 93 had their sights set on a federal government building not far from the Pentagon, but were forced to crash the plane in a Pennsylvania field when the passengers fought for control after being alerted to the previous suicide attacks, including Flight 77's.

The damaged sections of the Pentagon were rebuilt in 2002, with occupants moving back into the completed areas that August. The 184 victims of the attack are memorialized in the Pentagon Memorial adjacent to the crash site. The 1.93 acre park contains a bench for each of the victims, arranged according to their year of birth.

Background
The flight was commandeered as part of the September 11 attacks. The attacks themselves cost somewhere in the region of $400,000 and $500,000 to execute, but the source of this financial support remains unknown. Led by Khalid Sheikh Mohammed, who was described as being the "principal architect" of the attacks in the 9/11 Commission Report, al-Qaeda was motivated by several factors, not least of which was anti-Americanism and anti-Western sentiment. Because al-Qaeda only had the resources to commandeer four passenger jets, there was disagreement between Mohammed and Osama bin Laden over which targets should be prioritized. Mohammed favored striking the Twin Towers of the World Trade Center complex in New York City, while bin-Laden was bent on toppling the United States federal government, a goal he believed could be accomplished by destroying the Pentagon, the White House and the United States Capitol. Though bin Laden himself expressed a preference for the destruction of the White House over the Capitol, his subordinates disagreed, citing its difficulty in striking from the air. Hani Hanjour―likely while in the presence of fellow Flight 77 accomplice Nawaf al-Hazmi―scoped out the Washington metropolitan area on July 20, 2001 by renting a plane and taking a practice flight from Fairfield, New Jersey to Gaithersburg, Maryland in order to determine the feasibility of each of the possible candidates.

In the end, 19 terrorists participated in the attacks against the United States, consisting of three groups of five men each and one group of four. The nine hijackers on Flight 77 and United Airlines Flight 93 were assigned the task of striking governmental structures in or near the national capital of Washington, D.C., and as such, the objective was for the two hijackings to be coordinated insofar as both planes being aimed towards targets in the Washington metropolitan area. Significant complications faced by the four terrorists on Flight 93 ensured that Flight 77 was the only one to successfully attack a target intended by al-Qaeda when it struck the Pentagon in Arlington County, Virginia at 09:37, while a passenger uprising forced the hijackers aboard Flight 93 to crash the plane in rural Pennsylvania.

Regardless, the degree of coordination between Flight 77 and Flight 93 was evidently less than that of American Airlines Flight 11 and United Airlines Flight 175, the two airliners that were flown into the Twin Towers of the World Trade Center 17 minutes apart in a joint attack on New York City. Flights 11 and 175 both departed from Logan International Airport in Boston for Los Angeles International Airport, and crashed into targets that stood next to each other, in contrast to the Pentagon and the federal government building Flight 93 was set to crash into, which were simply located in the same general area.

One noteworthy difference between the attacks in the National Capital Region and those in New York is that the teams on Flights 77 and 93 did not follow suit with their counterparts on Flights 11 and 175 by booking planes from the same airport with the same California destination in mind. Flight 77's group hijacked a plane out of Dulles International Airport in Virginia, conveniently situated near the Pentagon and consequently the capital, on a flight path destined for LAX. Conversely, Flight 93 departed from Newark International Airport in New Jersey, nearly 200 miles northeast of D.C., bound for San Francisco International Airport. There was also no contact between Hanjour and Flight 93 hijacker pilot Ziad Jarrah on the day of the attacks, whereas Mohamed Atta and Marwan al-Shehhi spoke over the phone while preparing to board their respective flights, apparently to confirm the attacks were ready to begin.

The reason why al-Qaeda selected four planes from three airports instead of two airports remains unknown, but it is believed that the act of hijacking two planes on the same flight path would have enabled better coordination between the teams on Flight 11 and Flight 175, both of which clearly succeeded, unlike Flight 77 and Flight 93’s only partially successful attack on the U.S. government.

Hijackers
The hijackers on American Airlines Flight   77 were five Saudi men between the ages of 20 and 29. They were led by Hanjour, who piloted the aircraft into the Pentagon. Hanjour first arrived in the United States in 1990.

Hanjour trained at the CRM Airline Training Center in Scottsdale, Arizona, earning his FAA commercial pilot's certificate in April 1999. He had wanted to be a commercial pilot for Saudia but was rejected when he applied to the civil aviation school in Jeddah in 1999. Hanjour's brother later explained that, frustrated at not finding a job, Hanjour "increasingly turned his attention toward religious texts and cassette tapes of militant Islamic preachers." Hanjour returned to Saudi Arabia after being certified as a pilot, but left again in late 1999, telling his family he was going to the United Arab Emirates to work for an airline. Hanjour likely went to Afghanistan, where Al-Qaeda recruits were screened for special skills they might have. Already having selected the Hamburg cell members, Al Qaeda leaders selected Hanjour to lead the fourth team of hijackers.

In December 2000, Hanjour arrived in San Diego, joining "muscle" hijackers Nawaf al-Hazmi and Khalid al-Mihdhar, who had been there since January of that year. Alec Station, the CIA's unit dedicated to tracking Osama bin Laden, had discovered that al-Hazmi and al-Mihdhar had multiple-entry visas to the United States. An FBI agent inside the unit and his supervisor Mark Rossini (Former Federal Bureau of Investigation Supervisory Agent) sought to alert FBI headquarters, but the CIA officer supervising Rossini at Alec Station rebuffed him on the grounds that the FBI lacked jurisdiction.

Soon after arriving in San Diego, Hanjour and Hazmi left for Mesa, Arizona, where Hanjour began refresher training at Arizona Aviation. In April 2001, they relocated to Falls Church, Virginia, where they awaited the arrival of the remaining "muscle" hijackers. One of these men, Majed Moqed, arrived on May 2, 2001, with Flight   175 hijacker Ahmed al-Ghamdi from Dubai at Dulles International Airport. They moved into an apartment with Hazmi and Hanjour.

On May 21, 2001, Hanjour rented a room in Paterson, New Jersey, where he stayed with other hijackers through the end of August. The last Flight   77 "muscle" hijacker, Salem al-Hazmi, arrived on June 29, 2001, with Abdulaziz al-Omari (a hijacker of Flight    11) at John F. Kennedy International Airport from the United Arab Emirates. They stayed with Hanjour.

Hanjour received ground instruction and did practice flights at Air Fleet Training Systems in Teterboro, New Jersey, and at Caldwell Flight Academy in Fairfield, New Jersey. Hanjour moved out of the room in Paterson and arrived at the Valencia Motel in Laurel, Maryland, on September 2, 2001. While in Maryland, Hanjour and fellow hijackers trained at Gold's Gym in Greenbelt. On September 10, he completed a certification flight, using a terrain recognition system for navigation, at Congressional Air Charters in Gaithersburg, Maryland.

On September 10 Nawaf al-Hazmi, accompanied by other hijackers, checked into the Marriott in Herndon, Virginia, near Dulles Airport.

Suspected accomplices
According to a U.S. State Department cable leaked in the WikiLeaks dump in February 2010, the FBI has investigated another suspect, Mohammed al-Mansoori. He had associated with three Qatari citizens who flew from Los Angeles to London (via Washington) and Qatar on the eve of the attacks, after allegedly surveying the World Trade Center and the White House. U.S. law enforcement officials said the data about the four men was "just one of many leads that were thoroughly investigated at the time and never led to terrorism charges." An official added that the three Qatari citizens had never been questioned by the FBI. Eleanor Hill, the former staff director for the congressional joint inquiry on the September 11 attacks, said the cable reinforces questions about the thoroughness of the FBI's investigation. She also said that the inquiry concluded the hijackers had a support network that helped them in different ways.

The three Qatari men were booked to fly from Los Angeles to Washington on September 10, 2001, on the same plane that was hijacked and piloted into the Pentagon on the following day. Instead, they flew from Los Angeles to Qatar, via Washington and London. While the cable said Mansoori was currently under investigation, U.S. law enforcement officials said there was no active investigation of him or of the Qatari citizens mentioned in the cable.

Flight
The aircraft involved in the hijacking was a Boeing 757-223 (registration The aircraft had its first flight on April 25, 1991 and was delivered to American Airlines on May 8, 1991.  On September 11, the total flight duration was 77 minutes. The crew included Captain Charles Burlingame (51) (a Naval Academy graduate and former fighter pilot), First Officer David Charlebois (39), purser Renee May and flight attendants Michele Heidenberger, Jennifer Lewis and Kenneth Lewis. The capacity of the aircraft was 188 passengers, but with 58 passengers on September 11, the load factor was 33 percent. American Airlines said Tuesdays were the least-traveled day of the week, with the same load factor seen on Tuesdays in the previous three months for Flight    77. Passenger Barbara Olson, whose husband Theodore Olson served as the 42nd Solicitor General of the United States, was en route to a recording of the TV show Politically Incorrect. A group of three 11-year-old children, their chaperones, and two National Geographic Society staff members were also on board, embarking on an educational trip west to the Channel Islands National Marine Sanctuary near Santa Barbara, California. Former Georgetown University basketball coach John Thompson had originally booked a ticket on Flight   77. As he would tell the story many times in the following years, including a September 12, 2011 interview on Jim Rome's radio show, he had been scheduled to appear on that show on September 12, 2001. Thompson was planning to be in Las Vegas for a friend's birthday on September 13, and initially insisted on traveling to Rome's Los Angeles studio on the 11th. However, this did not work for the show, which wanted him to travel on the day of the show. After a Rome staffer personally assured Thompson he would be able to travel from Los Angeles to Las Vegas immediately after the show, Thompson changed his travel plans. He would later feel the impact from the crash at his home near the Pentagon.

Boarding and departure
On the morning of September 11, 2001, the five hijackers arrived at Washington Dulles International Airport. At 07:15 AM ET, Khalid al-Mihdhar and Majed Moqed checked in at the American Airlines ticket counter for Flight   77, arriving at the passenger security checkpoint a few minutes later at 07:18. Both men set off the metal detector and were put through secondary screening. Moqed continued to set off the alarm, so he was searched with a hand wand. The Hazmi brothers checked in together at the ticket counter at 07:29. Hani Hanjour checked in separately and arrived at the passenger security checkpoint at 07:35. Hanjour was followed minutes later at the checkpoint by Salem and Nawaf al-Hazmi, who also set off the metal detector's alarm. The screener at the checkpoint never resolved what set off the alarm. As seen in security footage later released, Nawaf al-Hazmi appeared to have an unidentified item in his back pocket. Utility knives up to four inches were permitted at the time by the Federal Aviation Administration (FAA) as carry-on items. The passenger security checkpoint at Dulles International Airport was operated by Argenbright Security, under contract with United Airlines.

The hijackers were all selected for extra screening of their checked bags. Hanjour, al-Mihdhar, and Moqed were chosen by the Computer Assisted Passenger Prescreening System (CAPPS) criteria, while the brothers Nawaf and Salem al-Hazmi were selected because they did not provide adequate identification and were deemed suspicious by the airline check-in agent. Hanjour, Mihdhar, and Nawaf al-Hazmi did not check any bags for the flight. Checked bags belonging to Moqed and Salem al-Hazmi were held until they boarded the aircraft.

Flight 77 was scheduled to depart for Los Angeles at 08:10; 58 passengers boarded through Gate D26, including the five hijackers. The 53 other passengers on board excluding the hijackers were 26 men, 22 women, and five children ranging in age from three to eleven. On the flight, Hani Hanjour was seated up front in 1B, while Salem and Nawaf al-Hazmi were likewise seated in first class, in seats 5E and 5F. Majed Moqed and Khalid al-Mihdhar were seated farther back in 12A and 12B, in economy class. Flight   77 left the gate on time and took off from Runway 30 at Dulles at 08:20. The attacks were already underway by this point, as American Airlines Flight 11 had been hijacked six minutes earlier. Shortly after Flight 77 became airborne, FAA flight controller Danielle O'Brien made a routine handoff of the flight to a colleague at the FAA's Indianapolis Center. For reasons she could not explain and would never fully understand, O'Brien did not use one of her normal sendoffs to the pilots: "Good day," or "Have a nice flight." Instead, she wished them, "Good luck."

Flight 77 reached its assigned cruising altitude of 35,000 feet at 8:46 a.m., four minutes after the hijacking of United Airlines Flight 175 commenced and the very same minute Flight 11 crashed into the North Tower of the World Trade Center. The final communication between Flight 77 and controllers on the ground occurred four minutes later at 08:50:51, as Hanjour and his team prepared to strike.

Hijacking

The terrorists launched their assault at 08:51, by which point the North Tower had been on fire for around five minutes and Flight 175 was within 12 minutes of striking the South Tower. Flight 93 had also become airborne from Newark at 08:42, but had been delayed on the runway for as long as 42 minutes and would not be seized until 09:28, preventing al-Qaeda's idea to synchronize its takeover with that of Flight 77. Three minutes after the hijacking began, according to the commission, the attackers on Flight 77 were in full control of the aircraft. The modus operandi of Hanjour’s group was in stark contrast to the other three teams, in that while the victims were threatened with knives and box cutters, there were no reports of any injuries or deaths prior to the crash; both pilots were spared when the cockpit was breached, and the use of chemical weapons or bomb threats was not reported by either of the two people who made phone calls from the rear of the cabin. At 08:54, as the plane flew in the vicinity over Pike County, Ohio, it began deviating from its normal assigned flight path and turned south. Two minutes later, the plane's transponder was switched off. The flight's autopilot was promptly engaged and set on a course heading eastbound towards Washington, D.C.

The FAA was aware at this point there was an emergency on board the airplane. After learning of a second hijacking involving an American Airlines aircraft and the hijacking of a United Airlines jet, American Airlines' executive vice president Gerard Arpey ordered a nationwide ground stop for the airline. For several minutes, Indianapolis Air Route Traffic Control Center and dispatchers for American Airlines made several failed attempts to contact the hijacked airliner, giving up just as Flight 175 flew into the World Trade Center's South Tower at 09:03. The plane had been flying over an area of limited radar coverage at the time of its hijacking. With air controllers unable to contact the flight by radio, an Indianapolis official declared that it had possibly crashed at 09:09, twenty-eight minutes before it actually did. Sometime between 09:17 and 09:22, Hanjour broadcast a deceptive announcement via the cabin’s public address system, advising those aboard that the plane was being hijacked and that their best chance of survival was by not resisting. This tactic was used on Flight 11 and on Flight 93 with the aim of deceiving the passengers and crew into believing the plan was to land the plane after securing a ransom; in both cases, however, the terrorists’ understanding of the internal communication systems used aboard aircraft was evidently not as good as Hanjour's, as they keyed the wrong microphone and broadcast their message to the ground instead. No passengers aboard Flight 11 reported hearing any intercom messages.

Calls
Two people on board the aircraft made a total of three phone calls to contacts on the ground. At 09:12, flight attendant Renee May made a phone call lasting just under two minutes to her mother, Nancy May, in Las Vegas. During the phone call, she made the erroneous claim that "six persons" had forced "us" to the rear of the airplane, but did not explain whether the people crowded together were crew members, passengers, or both. May asked her mother to contact American Airlines, which she and her husband promptly did, although the company was well aware of the hijacking by this point.

At 09:16, Barbara Olson made a call to her husband Ted, quietly explaining that the plane had been hijacked and that those responsible were armed with knives and box cutters. She revealed that everyone, including the pilots, had been moved to the back of the cabin and that the call was being made without the knowledge of the hostage takers. The connection dropped a minute into the conversation. Theodore Olson contacted the command center at the Department of Justice, and tried unsuccessfully to contact Attorney General John Ashcroft. Barbara Olson called again five minutes later, informing her husband of the announcement Hanjour―"the pilot"―made over the loudspeaker, and asked him, "What do I tell the pilot to do?" Inquired of her whereabouts, Barbara replied saying that they were flying low over a residential area. In the background, Ted overheard another passenger mentioning that the plane was flying northeast. He then made his wife aware of the suicide attacks on the World Trade Center, causing her to go quiet; Ted wondered if this meant she had been shocked into silence. After expressing their feelings and reassuring one another, the call cut off for the last time, at 9:26 a.m.

Crash

At 9:29 a.m., one minute after Flight 93 was hijacked, the terrorists aboard Flight 77 disengaged the autopilot and took manual control of the plane. Turning and descending rapidly as it made its final approach toward Washington, the airplane was detected again on radar screens by controllers at Dulles, who mistook it for a military fighter at first glance due to its high speed and maneuvering.

While Flight   77 was 5 mi west-southwest of the Pentagon in Arlington County, Virginia, it made a 330-degree spiral turn clockwise. By the end of the revolution, the 757 was descending 2200 ft, pointed toward the Pentagon and downtown Washington. Advancing the throttles to full power, Hanjour rapidly began diving toward his target. The wings clipped five street lights as the plane flew level above the ground, while the right wing in particular struck a portable generator, creating a smoke trail seconds before smashing into the Pentagon.

Flying at a speed of 530 mph over the Navy Annex Building adjacent to Arlington National Cemetery, Flight   77 crashed into the Pentagon's western flank at 09:37:46. The plane struck the establishment at the first-floor level and was rolled slightly to the left, with the right wing elevated as it crashed. The front part of the fuselage immediately disintegrated upon impact, while the mid and tail sections continued moving for another fraction of a second, with tail section debris penetrating farthest into the building. In total, the aircraft took eight-tenths of a second to pass 310 ft through the three outermost of the structure's five rings and unleashed a fireball that rose 200 ft above the building. The 64 people aboard the flight were killed instantly, while a further 125 people in the Pentagon were either killed outright or fatally injured.

In the minutes leading up to the crash, Reagan Airport controllers had asked a passing Air National Guard Lockheed C-130 Hercules to identify and follow the aircraft. The pilot, Lieutenant Colonel Steven O'Brien, told them he believed it was either a Boeing   757 or 767, observing that its silver fuselage meant it was most likely an American Airlines jet. O'Brien mentioned having difficulty picking out the airplane in the "East Coast haze", but moments later reported seeing a "huge" fireball. His initial assumption as he approached the crash site was that the plane had simply hit the ground, but upon closer inspection he saw the damage done to the Pentagon's west side and relayed to Reagan control, "Looks like that aircraft crashed into the Pentagon, sir."

At the time of the attacks, approximately 18,000 people worked in the Pentagon, 4,000 fewer than before renovations began in 1998. The section of the Pentagon that was struck, which had recently been renovated at a cost of $250   million (~$ in ), housed the Naval Command Center.

The fatalities in the Pentagon included 55 military personnel and 70 civilians. Of those 125 killed, 92 were on the first floor, 31 were on the second floor, and two were on the third. Seven Defense Intelligence Agency civilian employees were killed while the Office of the Secretary of Defense lost one contractor. The U.S. Army suffered 75 fatalities – 53 civilians (47 employees and six contractors) and 22 soldiers – while the U.S. Navy suffered 42 fatalities – nine civilians (six employees and three contractors) and 33 sailors. Lieutenant General Timothy Maude, an Army deputy chief of staff, was the highest-ranking military officer killed at the Pentagon; also killed was retired Rear Admiral Wilson Flagg, a passenger on the plane. LT Mari-Rae Sopper, JAGC, USNR, was also on board the flight, and was the first Navy Judge Advocate ever to be killed in action. Another 106 were injured on the ground and were treated at area hospitals.

On the side where the plane hit, the Pentagon is bordered by Interstate 395 and Washington Boulevard. Motorist Mary Lyman, who was on I-395, saw the airplane pass over at a "steep angle toward the ground and going fast" and then saw the cloud of smoke from the Pentagon. Omar Campo, another witness, was on the other side of the road: "I was cutting the grass and it came in screaming over my head. I felt the impact. The whole ground shook and the whole area was full of fire. I could never imagine I would see anything like that here."

Afework Hagos, a computer programmer, was on his way to work and stuck in a traffic jam near the Pentagon when the airplane flew over. "There was a huge screaming noise and I got out of the car as the plane came over. Everybody was running away in different directions. It was tilting its wings up and down like it was trying to balance. It hit some lampposts on the way in." Daryl Donley witnessed the crash and took some of the first photographs of the site.

USA Today reporter Mike Walter was driving on Washington Boulevard when he witnessed the crash: "I looked out my window and I saw this plane, this jet, an American Airlines jet, coming. And I thought, 'This doesn't add up, it's really low.' And I saw it. I mean it was like a cruise missile with wings. It went right there and slammed right into the Pentagon."

Terrance Kean, who lived in a nearby apartment building, heard the noise of loud jet engines, glanced out his window, and saw a "very, very large passenger jet". He watched "it just plow right into the side of the Pentagon. The nose penetrated into the portico. And then it sort of disappeared, and there was fire and smoke everywhere." Tim Timmerman, who is a pilot himself, noticed American Airlines markings on the aircraft as he saw it hit the Pentagon. Other drivers on Washington Boulevard, Interstate 395, and Columbia Pike witnessed the crash, as did people in Pentagon City, Crystal City, and other nearby locations.

Rescue and recovery
Rescue efforts began immediately after the crash. Almost all the successful rescues of survivors occurred within half an hour of the impact. Initially, rescue efforts were led by the military and civilian employees within the building. Within minutes, the first fire companies arrived and found these volunteers searching near the impact site. The firemen ordered them to leave as they were not properly equipped or trained to deal with the hazards.

The Arlington County Fire Department (ACFD) assumed command of the immediate rescue operation within ten minutes of the crash. ACFD Assistant Chief James Schwartz implemented an incident command system (ICS) to coordinate response efforts among multiple agencies. It took about an hour for the ICS structure to become fully operational. Firefighters from Fort Myer and Reagan National Airport arrived within minutes. Rescue and firefighting efforts were impeded by rumors of additional incoming planes. Chief Schwartz ordered two evacuations during the day in response to these rumors.

As firefighters attempted to extinguish the fires, they watched the building in fear of a structural collapse. One firefighter remarked that they "pretty much knew the building was going to collapse because it started making weird sounds and creaking." Officials saw a cornice of the building move and ordered an evacuation. Minutes later, at 10:10, the upper floors of the damaged area of the Pentagon collapsed. The collapsed area was about 95 ft at its widest point and 50 ft at its deepest. The amount of time between impact and collapse allowed everyone on the fourth and fifth levels to evacuate safely before the structure collapsed. After 11:00, firefighters mounted a two-pronged attack against the fires. Officials estimated temperatures of up to 2000 °F. While progress was made against the interior fires by late afternoon, firefighters realized a flammable layer of wood under the Pentagon's slate roof had caught fire and begun to spread. Typical firefighting tactics were rendered useless by the reinforced structure as firefighters were unable to reach the fire to extinguish it. Firefighters instead made firebreaks in the roof on September 12 to prevent further spreading. At 18:00 on the 12th, Arlington County issued a press release stating the fire was "controlled" but not fully "extinguished". Firefighters continued to put out smaller fires that ignited in the succeeding days.

Various pieces of aircraft debris were found within the wreckage at the Pentagon. While on fire and escaping from the Navy Command Center, Lt. Kevin Shaeffer observed a chunk of the aircraft's nose cone and the nose landing gear in the service road between rings B and C. Early in the morning on Friday, September 14, Fairfax County Urban Search and Rescue Team members Carlton Burkhammer and Brian Moravitz came across an "intact seat from the plane's cockpit", while paramedics and firefighters located the two black boxes near the punch out hole in the A–E drive, nearly 300 ft into the building. The cockpit voice recorder was too badly damaged and charred to retrieve any information, though the flight data recorder yielded useful information. Investigators also found a part of Nawaf al-Hazmi's driver's license in the North Parking Lot rubble pile. Personal effects belonging to victims were found and taken to Fort Myer.

Remains

Army engineers determined by 17:30 on the first day that no survivors remained in the damaged section of the building. In the days after the crash, news reports emerged that up to 800 people had died. Army soldiers from Fort Belvoir were the first teams to survey the interior of the crash site and noted the presence of human remains. Federal Emergency Management Agency (FEMA) Urban Search and Rescue teams, including Fairfax County Urban Search and Rescue assisted the search for remains, working through the National Interagency Incident Management System (NIIMS). Kevin Rimrodt, a Navy photographer surveying the Navy Command Center after the attacks, remarked that "there were so many bodies, I'd almost step on them. So I'd have to really take care to look backwards as I'm backing up in the dark, looking with a flashlight, making sure I'm not stepping on somebody." Debris from the Pentagon was taken to the Pentagon's north parking lot for more detailed search for remains and evidence.

Remains recovered from the Pentagon were photographed, and turned over to the Armed Forces Medical Examiner office, located at Dover Air Force Base in Delaware. The medical examiner's office was able to identify remains belonging to 179 of the victims. Investigators eventually identified 184 of the 189 people who died in the attack. The remains of the five hijackers were identified through a process of elimination, and were turned over as evidence to the Federal Bureau of Investigation (FBI). On September 21, the ACFD relinquished control of the crime scene to the FBI. The Washington Field Office, National Capital Response Squad (NCRS), and the Joint Terrorism Task Force (JTTF) led the crime scene investigation at the Pentagon.

By October 2, 2001, the search for evidence and remains was complete and the site was turned over to Pentagon officials. In 2002, the remains of 25 victims were buried collectively at Arlington National Cemetery, with a five-sided granite marker inscribed with the names of all the victims in the Pentagon. The ceremony also honored the five victims whose remains were never found.

Flight recorders

About 03:40 on September 14, a paramedic and a firefighter who were searching through the debris of the impact site found two dark boxes, about 1.5 by long. They called for an FBI agent, who in turn called for someone from the National Transportation Safety Board (NTSB). The NTSB employee confirmed that these were the flight recorders ("black boxes") from American Airlines Flight   77. Dick Bridges, deputy manager for Arlington County, Virginia, said the cockpit voice recorder was damaged on the outside and the flight data recorder was charred. Bridges said the recorders were found "right where the plane came into the building".

The cockpit voice recorder was transported to the NTSB lab in Washington, D.C., to see what data was salvageable. In its report, the NTSB identified the unit as an L-3 Communications, Fairchild Aviation Recorders model A-100A cockpit voice recorder – a device which records on magnetic tape. There were several loose pieces of magnetic tape that were found lying inside of the tape enclosure. No usable segments of tape were found inside the recorder; according to the NTSB's report, "[t]he majority of the recording tape was fused into a solid block of charred plastic". On the other hand, all the data from the flight data recorder, which used a solid-state drive, was recovered.

Continuity of operations
At the moment of impact, Secretary of Defense Donald Rumsfeld was in his office on the other side of the Pentagon, away from the crash site. He ran to the site and assisted the injured. Rumsfeld returned to his office, and went to a conference room in the Executive Support Center where he joined a secure videoteleconference with Vice President Dick Cheney and other officials. On the day of the attacks, DoD officials considered moving their command operations to Site R, a backup facility in Pennsylvania. Secretary of Defense Rumsfeld insisted he remain at the Pentagon, and sent Deputy Secretary Paul Wolfowitz to Site R. The National Military Command Center (NMCC) continued to operate at the Pentagon, even as smoke entered the facility. Engineers and building managers manipulated the ventilation and other building systems that still functioned to draw smoke out of the NMCC and bring in fresh air.

During a press conference held inside the Pentagon at 18:42, Rumsfeld announced, "The Pentagon's functioning. It will be in business tomorrow." Pentagon employees returned the next day to offices in mostly unaffected areas of the building. By the end of September, more workers returned to the lightly damaged areas of the Pentagon.

Aftermath

Early estimates on rebuilding the damaged section of the Pentagon were that it would take three years to complete. However, the project moved forward at an accelerated pace and was completed by the first anniversary of the attack. The rebuilt section of the Pentagon includes a small indoor memorial and chapel at the point of impact. An outdoor memorial, commissioned by the Pentagon and designed by Julie Beckman and Keith Kaseman, was completed on schedule for its dedication on September 11, 2008.

Security camera videos

The Department of Defense released filmed footage on May 16, 2006, that was recorded by a security camera of American Airlines Flight   77 crashing into the Pentagon, with a plane visible in one frame, as a "thin white blur" and an explosion following. The images were made public in response to a December 2004 Freedom of Information Act request by Judicial Watch. Some still images from the video had previously been released and publicly circulated, but this was the first official release of the edited video of the crash.

A nearby Citgo service station also had security cameras, but a video released on September 15, 2006, did not show the crash because the camera was pointed away from the crash site.

The Doubletree Hotel in the nearby neighborhood of Crystal City also had a security camera video. The FBI released the video on December 4, 2006, in response to a FOIA lawsuit filed by Scott Bingham. The footage is "grainy and the focus is soft, but a rapidly growing tower of smoke is visible in the distance on the upper edge of the frame as the plane crashes into the building."

Memorials
On September 12, 2002, Defense Secretary Donald Rumsfeld and General Richard Myers, Chairman of the Joint Chiefs of Staff, dedicated the Victims of Terrorist Attack on the Pentagon Memorial at Arlington National Cemetery. The memorial specifically honors the five individuals for whom no identifiable remains were found. This included Dana Falkenberg, age three, who was aboard American Airlines Flight   77 with her parents and older sister. A portion of the remains of 25 other victims are also buried at the site. The memorial is a pentagonal granite marker 4.5 ft high. On five sides of the memorial along the top are inscribed the words "Victims of Terrorist Attack on the Pentagon September 11, 2001". Aluminum plaques, painted black, are inscribed with the names of the 184 victims of the terrorist attack. The site is located in Section 64, on a slight rise, which gives it a view of the Pentagon.

At the National September 11 Memorial, the names of the Pentagon victims are inscribed on six panels at the South Pool.

The Pentagon Memorial, located just southwest of The Pentagon in Arlington County, Virginia, is a permanent outdoor memorial to the 184 people who died as victims in the building and on American Airlines Flight   77 during the September    11 attacks. Designed by Julie Beckman and Keith Kaseman of the architectural firm of Kaseman Beckman Advanced Strategies with engineers Buro Happold, the memorial opened on September 11, 2008, seven years after the attack.

Nationalities of victims on the aircraft
The 53 passengers (excluding the hijackers) and six crew were from:

title: American Airlines Flight 77


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Ambush

An ambush is a surprise attack carried out by people lying in wait in a concealed position. The concealed position itself or the concealed person(s) may also be called an "". Ambushes as a basic fighting tactic of soldiers or of criminals have been used consistently throughout history, from ancient to modern warfare. The term "ambush" is also used in animal behavior studies, journalism, and marketing to describe methods of approach and strategy.

In the 20th century, a military ambush might involve thousands of soldiers on a large scale, such as at a choke point like a mountain pass. Conversely, it could involve a small irregular band or insurgent group attacking a regular armed-force patrol. Theoretically, a single well-armed, and concealed soldier could ambush other troops in a surprise attack.

In recent centuries, a military ambush can involve the exclusive or combined use of improvised explosive devices (IED). This allows attackers to hit enemy convoys or patrols while minimizing the risk of being exposed to return fire.

History
The use of ambush tactics by early people dates as far back as two million years when anthropologists have recently suggested that ambush techniques were used to hunt large game.

One example from ancient times is the Battle of the Trebia River. Hannibal encamped within striking distance of the Romans with the Trebia River between them, and placed a strong force of cavalry and infantry in concealment, near the battle zone. He had noticed, says Polybius, a "place between the two camps, flat indeed and treeless, but well adapted for an ambuscade, as it was traversed by a water-course with steep banks, densely overgrown with brambles and other thorny plants, and here he proposed to lay a stratagem to surprise the enemy". When the Roman infantry became entangled in combat with his army, the hidden ambush force attacked the Roman infantry in the rear. The result was slaughter and defeat for the Romans. Nevertheless, the battle also displays the effects of good tactical discipline on the part of the ambushed force. Although most of the legions were lost, about 10,000 Romans cut their way through to safety, maintaining unit cohesion. This ability to maintain discipline and break out or maneuver away from a kill zone is a hallmark of good troops and training in any ambush situation.

Ambushes were widely used by the Lusitanians, in particular by their chieftain Viriathus. Their usual tactic, called concursare, involved repeatedly charging and retreating, forcing the enemy to eventually give them chase, to set up ambushes in difficult terrain where allied forces would be awaiting. In his first victory, he eluded the siege of Roman praetor Gaius Vetilius and attracted him to a narrow pass next to the Barbesuda river, where he destroyed his army and killed the praetor. Viriathus's ability to turn chases into ambushes would grant him victories over a number of Roman generals.

Another Lusitanian ambush was performed by Curius and Apuleius on Roman general Quintus Fabius Maximus Servilianus, who led a numerically superior army complete with war elephants and Numidian cavalry. The ambush allowed Curius and Apuleius to steal Servilianus's loot train. However, a tactic error in their retreat led to the Romans retaking the train and putting the Lusitanians to flight. Viriathus later defeated Servilianus with a surprise attack.

Germanic war chief Arminius sprung an ambush against the Romans at Battle of the Teutoburg Forest. This particular ambush was to affect the course of Western history. The Germanic forces demonstrated several principles needed for a successful ambush. They took cover in difficult forested terrain, allowing the warriors time and space to mass without detection. They had the element of surprise, and this was also aided by the defection of Arminius from Roman ranks prior to the battle. They sprang the attack when the Romans were most vulnerable; when they had left their fortified camp, and were on the march in a pounding rainstorm.

The Germans did not dawdle at the hour of decision but attacked quickly, using a massive series of short, rapid, vicious charges against the length of the whole Roman line, with charging units sometimes withdrawing to the forest to regroup while others took their place. The Germans also used blocking obstacles, erecting a trench and earthen wall to hinder Roman movement along the route of the killing zone. The result was a mass slaughter of the Romans and the destruction of three legions. The Germanic victory caused a limit on Roman expansion in the West. Ultimately, it established the Rhine as the boundary of the Roman Empire for the next four hundred years, until the decline of the Roman influence in the West. The Roman Empire made no further concerted attempts to conquer Germania beyond the Rhine.

There are many notable examples of ambushes during the Roman-Persian Wars. A year after their victory at Carrhae, the Parthians invaded Syria but were driven back after a Roman ambush near Antigonia. Roman Emperor Julian was mortally wounded in an ambush near Samarra in 363 during the retreat from his Persian campaign. A Byzantine invasion of Persian Armenia was repelled by a small force at Anglon who performed a meticulous ambush by using the rough terrain as a force multiplier and concealing in houses. Heraclius' discovery of a planned ambush by Shahrbaraz in 622 was a decisive factor in his campaign.

Arabia during Muhammad's era
According to Muslim tradition, Islamic Prophet Muhammad used ambush tactics in his military campaigns. His first such use was during the Caravan raids. In the Kharrar caravan raid, Sa'd ibn Abi Waqqas was ordered to lead a raid against the Quraysh. His group consisted of about twenty Muhajirs. This raid was about a month after the previous one. Sa'd, with his soldiers, set up an ambush in the valley of Kharrar on the road to Mecca and waited to raid a Meccan caravan returning from Syria. However, the caravan had already passed and the Muslims returned to Medina without any loot.

Arab tribes during Muhammad's era also used ambush tactics. One example retold in Muslim tradition is said to have taken place during the First Raid on Banu Thalabah. The Banu Thalabah tribe were already aware of the impending attack; so they lay in wait for the Muslims. When Muhammad ibn Maslama arrived at the site, the Banu Thalabah with 100 men ambushed the Muslims while they were making preparation to sleep and, after a brief resistance, killed them all except for Muhammad ibn Maslama, who feigned death. A Muslim who happened to pass that way found him and assisted him to return to Medina. The raid was unsuccessful.

Procedure
In modern warfare, an ambush can be employed by ground troops up to platoon size against enemy targets, which may be other ground troops, or possibly vehicles. However, in some situations, especially when deep behind enemy lines, the actual attack will be carried out by a platoon. A company-sized unit will be deployed to support the attack group, setting up and maintaining a forward patrol harbour from which the attacking force will deploy, and to which they will retire after the attack.

Planning
Ambushes are complex multiphase operations and are therefore usually planned in some detail. First, a suitable killing zone is identified. This is where the ambush will be laid, where enemy units are expected to pass, and gives reasonable cover for the deployment, execution, and extraction phases of the ambush patrol. A path along a wooded valley floor would be a typical example.

Ambush can be described geometrically as:
 * Linear, when a number of firing units are equally distant from the linear kill zone. It can easily be controlled under all visibility conditions.
 * L-shaped, when a short leg of firing units are placed to enfilade (fire the length of) the sides of the linear kill zone.
 * V-shaped, when the firing units are distant from the kill zone where the enemy enters and the firing units lay down bands of intersecting and interlocking fire. This ambush is normally triggered only when the enemy is well into the kill zone. The intersecting bands of fire prevent any attempt of moving out of the kill zone.

Ambush criteria
The terrain for the ambush had to meet strict criteria:
 * provide concealment to prevent detection from the ground or air
 * enable ambush force to deploy, encircle and divide the enemy
 * allow for heavy weapons emplacements to provide sustained fire
 * enable the ambush force to set up observation posts for early detection of the enemy
 * permit the secret movement of troops to the ambush position and the dispersal of troops during withdrawal

One important feature of the ambush was that the target units should 'pile up' after being attacked, thus preventing them any easy means of withdrawal from the kill zone and hindering their use of heavy weapons and supporting fire. Terrain was usually selected which would facilitate this and slow down the enemy. Any terrain around the ambush site which was not favourable to the ambushing force, or which offered some protection to the target, was heavily mined and booby trapped or pre-registered for mortars.

Ambush units
The NVA/VC ambush formations consisted of:
 * lead-blocking element
 * main-assault element
 * rear-blocking element
 * observation posts
 * command post

Other elements might also be included if the situation demanded, such as a sniper screen along a nearby avenue of approach to delay enemy reinforcements.

Command posts
When deploying into an ambush site, the NVA first occupied several observation posts, placed to detect the enemy as early as possible and to report on the formation it was using, its strength and firepower, as well as to provide early warning to the unit commander. Usually, one main OP and numerous secondary OPs were established. Runners and radios were used to communicate between the OPs and the main command post. The OPs were located so that enemy movement into the ambush could be observed. They would remain in position throughout the ambush to report routes of reinforcement and withdrawal by the enemy, as well as his manoeuvre options. Frequently the OPs were reinforced to squad size and served as flank security. The command post was situated in a central location, frequently on terrain which afforded it a vantage point overlooking the ambush site.

Recon methods
Reconnaissance elements observing a potential ambush target on the move generally stayed 300–500 meters away. A "leapfrogging" recon technique can be used. Surveillance units were echeloned one behind the other. As the enemy drew close to the first, it fell back behind the last recon team, leaving an advance group in its place. This one in turn fell back as the enemy again closed the gap, and the cycle rotated. This method helped keep the enemy under continuous observation from a variety of vantage points, and allowed the recon groups to cover one another.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Ambush


text:
Talk:Acetylene

Untitled
Bryan, I note the very close similarity between this acetylene article and the one I put under "Links." This is almost too close for comfort...actually it is too close for comfort.

Perhaps, if the article were developed further, it wouldn't look so much like copyright infringement. --LMS

Not sure what to do with it other than simply rearranging the sentances more and perhaps substituting synonyms; this is pretty close to a simple list of facts, and facts are uncopyrightable. I'll give it a shot, though. -BD

 * Which article?

What's that stuff?
What is the black substance that comes off from the flame and floats away into the air when starting up an oxy-acetelyne torch?

 * Lampblack. Of course, it wouldn't be surprising to find it contains buckyballs as well.

 * Atlant 22:02, 30 March 2006 (UTC)

wha?
Please correct the following: a liquid does not sublime, by definition. A material can not sublime at its boiling point, again by definition (although there may be exceptions...) The boiling point can not be BELOW the melting point (under the same pressure and temperature).
 * I changed the melting point to the latest (1931) value reported in the webbook 171.65 K (link: http://webbook.nist.gov/cgi/cbook.cgi?ID=C74862&Units=SI&Mask=4#Thermo-Phase). Marenero (talk) 20:49, 16 July 2012 (UTC)
 * I believe this change is based on an error. Rather than add a long explanation in the middle of this old discussion, I have added a new section below. See Talk:Acetylene Dirac66 (talk) 01:42, 17 July 2012 (UTC)

The completely trivial (sorry, guys) list of side combustion products is unenlightening and certainly incomplete (eg how about NOx compounds and COR or COOR where R is multitude). The opinion that the sweet smell of pure C2H2 is pleasant is not in accord with my experience. The last paragraph is in dire need of rewriting. Its only partially intelligible and has garbled syntax and grammar. One of your links states that polymerization can occur at 15 psig. So which is it? The 1st paragraph has a run on sentence that is one for the books. Is it transported in acetone? If so then why not mention it. Whats the pressure in a tank or a tanker? No mention of toxicity. 400 C is NOT a low temperature for a hydrocarbon (with multiple bonds).

Acetylene can be easily stored in pressurized gas cylinders. What do you think how people weld? They have to tanks oxygen and acetylene. The acetylene is definetely not dissolved in acetone. It is correct that acetylene may explade at 100 kPa pressure (which is 1 atmosphere) but only in the presence of oxygen. It won't do anything on its own. Also the acetylene oxygene flame is one of the hottest burning flame of any hydrocarbon we know

 * From my distant memory Acetylene will decompose at around 15psi spontaneously, releasing lots of energy (in an explosion). It is stored in Acetone in welding cylinders to prevent this (as it dissolves readily and thus has a lower partial pressure).  There are hotter flames using different oxidisers or reducers, but acetylene + oxygen is the hottest hydrocarbon - oxygen flame AFAIK. --njh 11:41, 25 May 2006 (UTC)

Acetylene or ethyne
Why does the article claim that the chemical name of the compound is acetylene when it should be ethyne? In alkyne it states that the acetylene is officially known as ethyne which I assume is refering to IUPAC nomenclature.

 * I think that we should use IUPAC names everywhere and then have redirects from common names, rather than the alternative. But it'll never happen.Jaredjeya (talk) 20:56, 7 November 2014 (UTC)

 * I think we should follow the usage of most recent textbooks and scientific articles. IUPAC is not the only authority. Dirac66 (talk) 14:13, 9 November 2014 (UTC)

if you told me acetylene, i never would have thought it would be ethyne! stick to iupac! RaftaReads (talk) 17:07, 23 September 2020 (UTC)

Why "acetylene"?
Why is the compound even called acetylene at all? I see no similarities to the acetyl radical. No methyls, no carbonyls (not even an oxygen atom), nothing.

 * The OED gives the etymology as [f. ACETYL  + Gr. -ηνη female descendant, weaker derivative: see -ENE.

 * The Oxford Dictionary of English gives the origin as: mid 19th cen.: from acetic acid + -yl + -ene.

 * See also EtymOnline, Wiktionary:Acetylene, reactions of alkynes.

 * Acetylene can be hydrated to acetaldehyde, which contains the acetyl group and may account for the name. Acetyl compounds could, in principle at least, be dehydrated (often a facile reaction, no change in oxidation state) to C2H4 - an unsaturated hydrocarbon (hence -ene) from an acetyl group, hence acetylene.

 * Acetylene-hydration-2D.png

 * Ben (talk) 19:04, 2 February 2009 (UTC)

But the hydrated form is not the educt, which is called acetylene. (??!!) alternatively: acidify ethylene glycol, acetethylene(glycol)--> acet(h)ylene (ethylene glycol --> -H2O --> ethylene oxide/epoxide--> -H2O --> acetylene; epoxide may polymerize, but sulfuric acid can dehydrate the epoxide, I guess)--Smiles :( :\ :o : (talk) 02:56, 11 April 2015 (UTC)

Why?
History and tradition, most likely some misconception by the person(s) who first discovered or synthesized it.

Look up how hydrocarbon came about from early experimenters calling them 'watered carbons' due to all the hydrogen in them which had to be an indicator of water involved in the processes that create them. Of course the assumptions were wrong but hydrocarbon stuck as the name of that class of compounds.

 * You might be thinking of carbohydrates? --njh 11:43, 25 May 2006 (UTC)

Generation and storage
Here's a free e-book that contains plenty of information on the gas.

http://www.gutenberg.org/etext/7969

I've no idea how old it is, but the text has a "feel" to it that appears to date it to the early 20th century. There's no metric units mentioned and the terms 'Sulphuretted Hydrogen' instead of hydrogen sulphide and 'Phosphoretted Hydrogen' instead of phosphine are definately old terminology. Unfortunatly it's just the text, none of the illustrations are included.

Ethyne is far more appropriate
I think we all agree that acetylene is a silly old confusing name- please change it to ethyne

 * Wow. Now you only need to convince hundreds of thousands of welders, etc.

 * Google test:

 * Acetylene: 3,550,000 hits
 * Ethyne: 94,100 hits
 * Ethine: 12,900 hits

 * Atlant 17:26, 13 June 2006 (UTC)

Ethine is most DEFINITLY wrong!

Now in the past women wore corsets and were not allowed to vote! Thankfully we don't all live in the past!! :D

Times are a changing!

Acetylene does not make sense from a chemists Perspective wheras ethyne DOES

Whats the alcohol used to make vodka more than just potatoe water: is it "grain alchohol" or is it ethanol!

Give it a few years mate and you'll let women vote too! Blonde2max 18:55, 17 June 2006 (UTC)

Ethyne may be the correct name to chemists, but everyone else calls it acetylene. There are already redirects in place for "ethine" and "ethyne". Just add a sentence in the article that explains the confusion between acetylene and ethyne and be done with it.

Bizzako 2:28, 02 August 2006 (MDT)

 * Don't change it to ethyne. I'm a chemist and I call it acetylene.  Most simple, common chemical compounds are primarily known by their trivial (non-systematic) names.  Check out this page - it is an online version of IUPAC's Blue Book (organic nomenclature bible).  It categorically states that the name acetylene is retained.  That's straight from the horse's mouth.

 * What WP editors seem to be confused about is the difference between rigidly systematic nomenclature and IUPAC recommendations. Although in schools, we are generally taught to always use the systematic name, this is in fact for the purposes of education and to not overload students by making them learn loads of trivial names off by heart.  In scientific practice and in general commercial and industrial settings, calling acetylene by the name ethyne would usually be considered to be excessively pedantic and would most likely cause confusion.

 * In response to Blonde2max's comments, yes ethanol is generally called ethanol by chemists, but acetaldehyde is generally not called ethanal, nor is formaldehyde ever called methanal. Toluene is always used in preference to methylbenzene, as are many, many other compounds.  Acetone, not propanone.  Acetic acid, not ethanoic acid.  The list goes on.  Keep this page called acetylene.

 * Ben 21:05, 2 August 2006 (UTC)

 * I would disagree that formaldehyde is never called methanal, as well as other examples you give. It really depends on the generation of the person involved, especially when the IUPAC name is less cumbersome than the trivial one eg ethanal v acetaldehyde. In addition of course the IUPAC names reveal the relationships between different chemicals and avoid the silly situation of talking about say methanol being metabolised into formaldehyde when methanol to methanal would be much simpler. Booshank (talk) 14:39, 2 February 2009 (UTC)

IUPAC nomenclature rule A-3.2 notes that "The name "acetylene" for HC≡CH is retained." --Spoon! 08:53, 23 December 2006 (UTC)

I'm absolutely confident that calling ethyne ethyne will not create confusion, or if only perhaps amongst people who just use it for some technical purposes and don't really care about what it actually is. And mind you, ethanoic acid, ethanal, methanal and propanone are the more commonly used forms of names in MODERN chemical literature. Trivial names are more often still used for complex yet common substances, such as toluene, glucose, etc. 129.67.54.6 (talk) 18:46, 20 January 2009 (UTC)

 * The modern chemical literature almost always calls HC≡CH acetylene, and the same goes for H3C-CO2H (always acetic acid), H3C-CHO always acetaldehyde), (H3C)2C=O (always acetone) and so on. I just checked SciFinder and Web of Science for HC≡CH in papers published since 2000. 8227 papers contain "acetylene", while only 439 refer to "ethyne" (ratio of 19:1). I checked a few of the papers that do contain the word "ethyne", and all of them had it as part of a longer name, such as phenyltrimethylsilylethyne in Chem. Eur. J. 2008, 14, 11557–11564.

 * Ben (talk) 16:29, 2 February 2009 (UTC)

 * I wouldn't argue that ethanal is more common than acetaldehyde, but to say it is always acetaldehyde is plainly incorrect. See for example just three I found from a simple search:-

 * Abatement of volatile organic compounds: oxidation of ethanal over niobium oxide-supported palladium-based catalysts http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFG-47CH5X3-G&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fa4c0401af4c301a6b5c654e0f7f2275

 * Numerical Studies of a Thermokinetic Model for Oscillatory Cool Flame and Complex Ignition Phenomena in Ethanal Oxidation Under Well-Stirred Flowin Conditions http://journals.royalsociety.org/content/603389500572155m/fulltext.pdf

 * An ab initio study of muons in ethanal: http://www.iop.org/EJ/abstract/0953-8984/9/15/015

Ethanal etc are plainly perfectly acceptable, if not the most common forms. Booshank (talk) 19:29, 2 February 2009 (UTC)

 * There are a few chemistry papers that use "ethanal" (although one of those papers was a physics one), but acetaldehyde is far more common (ethanal 77, acetaldehyde 4983, ratio 65:1, WoS, 2000-2009). Similarly, ethanoic acid 114 papers, acetic acid 22809, ratio 200:1 and methanal 69, formaldehyde 12381, ratio 179:1.

 * I think you see the point. You're right that there's nothing incorrect about ethyne etc, but the article name should clearly remain acetylene.

 * Ben (talk) 19:46, 2 February 2009 (UTC)

 * I am not arguing for the page to be renamed Ethyne as it is obviously not the most commonly used term, which is the Wikipedia criteria. I prefer ethyne as it is more logical and more concise in my opinion, but that is beside the point. What I am arguing for is against an unnecessary snootiness in regards to the systematic names and that the name ethyne should be prominent in the article as a) it is considered acceptable by IUPAC and is to be found in scientific literature and b) it is the name most encounter when learning chemistry. Acetylene is not a substance in everyday use by most people and therefore ethyne will be the only name encountered by many. Booshank (talk) 22:50, 2 February 2009 (UTC)

 * Be bold and make the changes you think appropriate. Then we can discuss them here. Make sure it's clear that acetylene outnumbers ethyne in the literature by around 20:1.

 * You say that most people don't encounter acetylene (depends how you mean encounter!) but I've known there is a substance called acetylene since I was about six years old (probably because of oxy-acetylene lamps), yet I only came across the term ethyne when I was 14 and studying GCSE science. I don't think alkynes were actually on the syllabus so I might not have seen the word ethyne until I did A-level chemistry, aged 17. Considering that most people do not take chemistry beyond GCSE (and probably a similar situation worldwide), I imagine the majority of the public have heard the term acetylene and not ethyne.

 * Ben (talk) 08:09, 9 March 2009 (UTC)

bad wording? Acetylene is not so hot.
"Oxyacetylene is the hottest burning of all fuel gases." What counts as a fuel gas? There are hotter stuffs:. A whole bunch of poluynes go noncharted in thèrmokemistry. -lysdexia 20:40, 30 September 2006 (UTC)

Flawed Nanotechnology Concept?
In the "Uses" section: "'Acetylene has been proposed as a carbon feedstock for molecular manufacturing using nanotechnology. Since it does not occur naturally, using acetylene could limit out-of-control self-replication.'"

In the "Natural occurrence" section: "'Acetylene is a moderately common chemical in the universe... Natural acetylene...'" How could the two quotes square with each other? Given the second one, the first is conceptually flawed. Shawn D. 16:37, 25 July 2007 (UTC)

Underwater?
We've been studying reactions in chemistry lately, and yesterday we demonstrated the synthesis and combustion of acetylene. Did I hear my teacher wrong when he said that some acetylene torches can burn underwater? —Preceding unsigned comment added by 71.190.143.208 (talk) 19:32, 25 October 2007 (UTC)

 * Acetylene torches have their own oxygen tank. Maybe that's enough to make them burn underwater? --Itub 14:53, 26 October 2007 (UTC)

 * The combination of the bottled acetylene combined with the bottled oxygen could theoretically allow it. However, on the torch tips I know of, the acetylene and oxygen streams combine externally after exiting individual holes -- the water could entrain the gases and prevent them from mixing and igniting or maintaining ignition. Shawn D. 15:46, 29 October 2007 (UTC)

 * I just looked at the article on oxy-fuel welding and cutting. From what it says, it seems to me that oxy-acetylene torches could work underwater, but only at very low pressures, so hydrogen is used instead. --Itub 08:50, 30 October 2007 (UTC)

Dallas acetylene fire
There was a major fire in Dallas, Texas a few years ago involving an welding company's headquarters. Hundred of tanks blew up, many hit the nearby freeway, nearly hitting cars (one direction of which was closed, the other wasn't). Is there an article for this? If there is, I can't find it. One of the amazing things is no one was killed. --98.232.182.66 (talk) 04:09, 21 September 2008 (UTC)

 * I found three articles quite easily on Google:

 * Fox News: Acetylene, Propane Gas Canister Explosions Rock Dallas

 * The Dallas Morning News: Dallas explosion injures 3, snarls traffic

 * There's also a New York Times comparison of this incident with a similar one in Houston.

 * Ben (talk) 11:50, 21 September 2008 (UTC)

Decomposition
The Compression section says "acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent." I can't find anywhere in the article, though, what it becomes when it decomposes. What are the decomposition products? Ian01 (talk) 04:14, 7 October 2008 (UTC)

 * Not sure, but I suspect carbon and hydrogen. I think what's meant by "fundamentally unstable" is that acetylene has a positive heat of formation; that is, the reaction H2 + 2C -> C2H2 is endothermic. --Itub (talk) 07:01, 7 October 2008 (UTC)

Is it true that acetylene tanks have to be stored and transported standing up and not lay on their sides?
I heard a rumor that you have to store and transport acetylene tanks standing up and that if you lay them on their sides they will explode?

I don't use acetylene, but I do use a GTAW welding rig with pressurized argon. My argon tank lays on its side in a cradle under my welding bench.

I think it's safer to have gas tanks lay on their sides and not standing up as they could not tip over if they are already laying on their sides.

I don't want to change the article because I only heard this as a rumor. Is there any cited source that talks about en explosion that is caused by someone laying an acetylene tank on it's side? Allyn (talk) 13:44, 25 July 2009 (UTC)

It is true that it is recommended to transport and store acetylene tanks in an upright position but not because they will explode it is because of the acetone in them. If acetone gets up to the valve and it can easily when the container is lying down you will have difficulties lighting up the torch. — Preceding unsigned comment added by 212.91.126.148 (talk) 05:59, 20 September 2011 (UTC)

I grew up with a story, from my father in some sort of chemistry, that the cylinders were acetylene in acetone in bentonite, and that laying down the cylinder would release the acetone from the bentonite and cause uncomfortable amounts of acetylene to come out of solution. I was a kid at the time, so if I've mangled the details, I won't be surprised. ArthurDent006.5 (talk) 07:03, 10 August 2014 (UTC)

 * This website United States Department of Labor: Special Hazards of Acetylene includes the words ACETYLENE CYLINDERS SHOULD BE STORED AND USED IN THE UPRIGHT POSITION AND FIRMLY SECURED TO PREVENT FALLING OR BEING KNOCKED OVER. (their capitals) Dirac66 (talk) 12:28, 10 August 2014 (UTC)

The tanks can be transported on their sides, but that is not recommended procedure. No harm will come to the tank, or acetylene. If they are laid horizontal, they have to be placed upright and left to stand for a period of time ( recommended several hour minimum ) until the acetone is given time to settle. If this does not happen, then the liquid acetone can get into the regulator and hoses, and cause sputtering of the flame, and potentially damage or failure of the equipment, notable the seals. Since acetylene is extremely flammable, a leaking cylinder in an enclosed space can create a violent explosion, frequently with no resulting after fire, as it can tend to blow itself out. — Preceding unsigned comment added by 70.121.157.34 (talk) 04:38, 20 March 2016 (UTC)

 * I have now added a link to the above noted US Dept of Labor (Mine Safety and Health Administration) site, which explicitly specifies the upright position. Dirac66 (talk) 16:02, 20 March 2016 (UTC)

Natural occurrence
Here's a link to an article that would seem to contradict the information in the Natural occurrence section.

http://www.newscientist.com/article/dn19005-hints-of-life-found-on-saturn-moon.html —Preceding unsigned comment added by SargeWallace (talk • contribs) 13:36, 6 June 2010 (UTC)

Move?

 * The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was: Speedy close (no move). No clear rationale provided for move and is contrary to WP:COMMONNAME so speedy close per WP:SNOW. Feel free to propose anew with a potentially persuasive rationale. Born2cycle (talk) 01:03, 15 January 2011 (UTC)

Acetylene → Ethyne —
 * WP:ALUM 75.15.161.185 (talk) 21:23, 14 January 2011 (UTC)
 * WP:ALUM says nothing that would impact the naming of this article. -- Ed (Edgar181) 21:41, 14 January 2011 (UTC)
 * Most people call it acetylene. Anthony Appleyard (talk) 21:32, 14 January 2011 (UTC)
 * Oppose: Naming_conventions_(chemistry) is the guideline to follow. "Acetylene" is by far the most common name in commercial, industrial, and academic settings.   -- Ed (Edgar181) 21:40, 14 January 2011 (UTC)
 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Melting point, boiling point, triple point, sublimation
From section wha? above:

1. Beginning of old comment (added 2005 Oct.1 by numbered editor) Please correct the following: a liquid does not sublime, by definition. A material can not sublime at its boiling point, again by definition (although there may be exceptions...) The boiling point can not be BELOW the melting point (under the same pressure and temperature). Etc.

2. Added today by Marenero:
 * I changed the melting point to the latest (1931) value reported in the webbook 171.65 K (link: http://webbook.nist.gov/cgi/cbook.cgi?ID=C74862&Units=SI&Mask=4#Thermo-Phase). Marenero (talk) 20:49, 16 July 2012 (UTC)

3. My comment: First, the phase behavior of acetylene is now explained in the article section Physical properties: changes of state. The triple point is at pressure higher than 1 atm, so the liquid can not exist at 1 atm (as for the better known case of CO2). The value given for the melting point is actually the triple point, and the value given for the boiling point is actually the sublimation point at 1 atm, and yes, this is lower than the triple point (again as for CO2).

Since melting point here actually means triple point, the latest value reported in the webbook is actually the 1950 value reported as a triple point, which is 192.4 K. This is close to the webbook values from before 1931, suggesting that the 1931 value is an error. The value in the article before today was actually this 1950 value fron the webbook.

Other more recent sources agree. The Handbook of Chemistry and Physics (60th edn 1979-80, page C-302) lists the melting point of ethyne as -80.8 oC, which is 192.35 K. And the Merck Index (13th edn 2001, p.17) says -81 oC with subl in parentheses. Therefore I suggest we return to the 1950 value. The infobox does note that it is the triple point at 1.27 atm, with more detailed explanation in the Physical properties section. Dirac66 (talk) 01:38, 17 July 2012 (UTC)

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Identifying Acetylene
I'm currently doing an apprenticeship for fabrication and in another fabrication book it notes that Acetylene has a strong garlic smell. would this be the "marked" odour that's mentioned at the beginning of this article? Wiki states that it is odourless in its pure form but has a marked odour commercially due to impurities. — Preceding unsigned comment added by 82.39.201.117 (talk) 08:49, 9 February 2021 (UTC)

Density
Hello, may you have different references or parameters, but your density is wrong. In the English version it is written 1,097 kg/m^3 (without information about the other parameters) but in the German one (with reference) with 1,1772 kg/m^3 (at standard conditions). Please correct or specify it. [Added 29 April 2021 by editor 2003:f9:872d:f806:a5dd:6a6c:2915:874]

 * The Infobox of this English article has a link at the bottom saying Infobox references, but it does not seem to lead to any useful statement of where the value 1,097 kg/m^3 comes from. In effect it is unsourced. On the other hand the value in the German article does have an intelligible source (even with my very limited German!), so I am tempted to just insert the value from the German article here, with the German reference. Does anyone have a better idea? Dirac66 (talk) 00:21, 19 May 2021 (UTC)

 * Done. I have now added the value and source from the German article. Dirac66 (talk) 18:11, 16 June 2021 (UTC)

Copyright problem removed
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Discovery: carbide reacts to form carbide??
The Discovery section now says: "By heating potassium carbide with carbon ... [Davy] produced a residue of what is now known as potassium carbide." How can potassium carbide react to form potassium carbide??

This was changed on 2022 January 2 from "By heating potassium carbonate with carbon ..." which at least had a reactant different from the product. However the reaction with carbonate was not very clear either - what happens to the oxygens?? And I cannot make much sense of the references given. Can someone make sense of this reaction and then correct the sentence? Dirac66 (talk) 03:32, 22 January 2022 (UTC)

Confusing sentence
From the "Discovery" section: "By heating potassium carbide with carbon at very high temperatures, he produced a residue of what is now known as potassium carbide, (K2C2), which reacted with water to release the new gas."

So he heated potassium carbide and got potassium carbide out of it? What is this sentence supposed to mean?

2A02:8108:96C0:6D08:1816:CC57:5704:15FB (talk) 17:52, 7 February 2022 (UTC)

 * It actually says "By heating potassium carbonate with carbon at very high temperatures, he produced a residue of what is now known as potassium carbide, ... Dirac66 (talk) 01:12, 12 May 2023 (UTC)

What is reduced carbon?
Perhaps I'm being dull but I'm not sure what "reduced carbon" is. The article says "oil supplanted coal as the chief source of reduced carbon".

Does it simply mean pure carbon (graphite), or does it mean carbon with a formal charge/oxidation state less than it normally is? In typical molecules such as hydrocarbons, carbon's formal charge tends to be 0. And it doesn't tend to be reduced further in reactions.

I feel that it's possible the editor related isolating pure carbon to isolating pure metals, which do tend to have a reduced oxidation state after the purifying process. But this would be an incorrect analogy.

But I may be missing something here and I haven't found out how to read or translate the cited source, so any insight's appreciated. 35drake (talk) 13:55, 1 February 2023 (UTC)

 * It means carbon with a lower oxidation state than the maximum of +4 in CO2. Dirac66 (talk) 01:07, 12 May 2023 (UTC)

title: Talk:Acetylene


text:
Abzyme

An abzyme (from antibody and enzyme), also called catmab (from catalytic monoclonal antibody), and most often called catalytic antibody or sometimes catab, is a monoclonal antibody with catalytic activity. Abzymes are usually raised in lab animals immunized against synthetic haptens, but some natural abzymes can be found in normal humans (anti-vasoactive intestinal peptide autoantibodies) and in patients with autoimmune diseases such as systemic lupus erythematosus, where they can bind to and hydrolyze DNA. To date abzymes display only weak, modest catalytic activity and have not proved to be of any practical use. They are, however, subjects of considerable academic interest. Studying them has yielded important insights into reaction mechanisms, enzyme structure and function, catalysis, and the immune system itself.

Enzymes function by lowering the activation energy of the transition state of a chemical reaction, thereby enabling the formation of an otherwise less-favorable molecular intermediate between the reactant(s) and the product(s). If an antibody is developed to bind to a molecule that is structurally and electronically similar to the transition state of a given chemical reaction, the developed antibody will bind to, and stabilize, the transition state, just like a natural enzyme, lowering the activation energy of the reaction, and thus catalyzing the reaction. By raising an antibody to bind to a stable transition-state analog, a new and unique type of enzyme is produced.

So far, all catalytic antibodies produced have displayed only modest, weak catalytic activity. The reasons for low catalytic activity for these molecules have been widely discussed. Possibilities indicate that factors beyond the binding site may play an important role, in particular through protein dynamics. Some abzymes have been engineered to use metal ions and other cofactors to improve their catalytic activity.

History
The possibility of catalyzing a reaction by means of an antibody which binds the transition state was first suggested by William P. Jencks in 1969. In 1994 Peter G. Schultz and Richard A. Lerner received the prestigious Wolf Prize in Chemistry for developing catalytic antibodies for many reactions and popularizing their study into a significant sub-field of enzymology.

Abzymes in healthy human breast milk
There are a broad range of abzymes in healthy human breast milk with DNAse, RNAse, and protease activity.

Potential HIV treatment
In a June 2008 issue of the journal Autoimmunity Review, researchers S. Planque, Sudhir Paul, Ph.D, and Yasuhiro Nishiyama, Ph.D of the University Of Texas Medical School at Houston announced that they have engineered an abzyme that degrades the superantigenic region of the gp120 CD4 binding site. This is the one part of the HIV virus outer coating that does not change, because it is the attachment point to T lymphocytes, the key cell in cell-mediated immunity. Once infected by HIV, patients produce antibodies to the more changeable parts of the viral coat. The antibodies are ineffective because of the virus' ability to change their coats rapidly. Because this protein gp120 is necessary for HIV to attach, it does not change across different strains and is a point of vulnerability across the entire range of the HIV variant population.

The abzyme does more than bind to the site: it catalytically destroys the site, rendering the virus inert, and then can attack other HIV viruses. A single abzyme molecule can destroy thousands of HIV viruses.

title: Abzyme