Pascal Zavaleta

Sylvain Suard

EXPERIMENTAL STUDY IN OPEN ATMOSPHERE AND CONFINED CONDITIONS OF FIRE SPREAD BETWEEN ADJACENT ELECTRICAL CABINETS CONNECTED BY CABLE TRAYS

Keywords: air gap, electrical cabinet, fire spread, overhead cable tray, subfloor cable tray, target ignition

Electrical cabinet-related fire events are among the most recorded fire events in nuclear power plants. As part of the OECD PRISME-3 project, four fire tests were carried out to highlight the fire spread paths from an open-door electrical cabinet (CC) to two adjacent closed-door electrical cabinets (ACs). The cabinets, separated by a double wall with an air gap, were connected by overhead and subfloor cable trays. These last ones were filled with either a "low" or "well-qualified" (LQ or WQ, respectively) cable type. Each cable type was used for two tests. In addition, tests were conducted either in open atmosphere conditions (two) or in confined and mechanically ventilated conditions (two). These tests highlighted three fire spread paths from the CC to the ACs. Regarding the first one through the double wall with an air gap, several ignitions of electrical components (used as targets) occurred in the ACs when the wall temperature near the ignited target exceeded 600 °C (or the heat flux incident to the target was higher than 26 kW/m 2 ) whatever the test conditions. Furthermore, the two other fire spread paths through the overhead and subfloor cable trays were highlighted only if the LQ cable type was used.

Introduction

Fire is a major hazard in many industrial sectors [START_REF] Thomson | Chapter 2, Fire Risk Assessment, Fire Hazards in Industry[END_REF] and especially in nuclear power plants (NPPs) [START_REF] Schneider | introduction to fire safety in nuclear power plants[END_REF]- [START_REF] Hukki | Development of Management of Nuclear Power Plant Fire Situations[END_REF]. Fire can affect the main safety functions of the NPPs such as the removal of the thermal power, the containment of radioactive substances or the protection measures [START_REF] Ormieres | IRSN global process for leading a comprehensive fire safety analysis for nuclear installations[END_REF]- [START_REF] Coutin | Characterization of open-doors electrical cabinet fires in compartments[END_REF]. International operating experience has also shown that some of the most challenging precursors to a core damage accident have involved internal fires [START_REF] Dey | Technical Review of Risk-Informed, Performance-Based Methods for Nuclear Power Plant Fire Protection Analyses[END_REF]- [START_REF] Kim | Maximum likelihood estimation of probabilistic non-suppression model for OECD NPP electrical fire applying non-negative continuous distribution[END_REF]. About 550 fire events from NPPs were recorded in the most recent version of the OECD/NEA FIRE (Fire Incidents Records Exchange) Database for the period from the 1980's to the end of 2017 [START_REF]Organisation for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA), Committee on the Safety of Nuclear Installations (CSNI), OECD/NEA FIRE Database Version 2019:01[END_REF]. In addition, Werner et al. [START_REF] Werner | Enhancements in the OECD fire database -Fire frequencies and severity of events[END_REF] mentioned that transformers and electrical cabinets were the most frequent fire sources with 47 and 45 fire events, respectively, that were recorded in the 2011 version of the above database [START_REF]OECD FIRE Database[END_REF]. Furthermore, about half of the fire start events recorded in French NPPs in the 2018-2020 period occurred in either electrical cabinets or electrical panels [START_REF]L'IRSN et les feux électriques : des recherches de grande intensité ![END_REF]. These equipment are indeed abundant in NPPs and they also represent a potential source of fire since they contain both combustible materials and live electrical circuits [START_REF] Avidor | Modarres Hazard assessment of fire in electrical cabinets[END_REF]- [START_REF] Gui | Experimental study on combustion characteristics of fire in data room[END_REF]. These circuits can undergo electrical failures, such as a short circuit * , overheating or electrical arcing [START_REF] Keski-Rahkonen | Electrical ignition sources in nuclear power plants: Statistical, modelling and experimental studies[END_REF]- [START_REF] Novak | An analysis of heat flux induced arc formation in a residential electrical cable[END_REF] that can ignite the combustible materials in the near vicinity. Fire probabilistic risk assessments (PRA) or probabilistic safety assessments (PSA) have been widely conducted for years to assess fire safety in NPPs [START_REF]EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities: Volume 1: Summary & Overview[END_REF]- [START_REF] Worrell | Fire Probabilistic Risk Assessment and its Applications in the Nuclear Power Industry[END_REF]. These studies have consistently found that fires involving electrical cabinets in key plant areas (including main control rooms, emergency switchgear rooms, cable spreading rooms, cable vaults and tunnels) are the dominant contributors against the fire safety of NPPs [START_REF]Fire Probabilistic Safety Assessments for Nuclear Power[END_REF], [START_REF]Methodology for Modeling Fire Growth and Suppression Response for Electrical Cabinet Fires in Nuclear Power Plants[END_REF]. In these areas, electrical cabinet fires could for instance damage nearby cables supporting important mitigating equipment or lead to the failure of a safety train [START_REF] Werner | Enhancements in the OECD fire database -Fire frequencies and severity of events[END_REF]. The work [START_REF]Methodology for Modeling Fire Growth and Suppression Response for Electrical Cabinet Fires in Nuclear Power Plants[END_REF] especially mentions that 47 electrical cabinet fire events, recorded in the database collected by EPRI and the U.S. NRC from NPPs across USA over 2000-2014 [START_REF]Nuclear Power Plant Fire Ignition Frequency and Non-Suppression Probability Estimation Using the Updated Fire Events Database[END_REF]- [START_REF]Fire Events Database Update for the Period[END_REF] were classified as potentially challenging or greater. Challenging fires are specified as fires which have observable and significant repercussions for the environment outside the initiating source. In another nuclear facilities, such as in the most complex particle accelerator facility, operated by CERN, a design fire calculator was recently developed to assess the fire hazard related to the numerous configurations of electrical cabinets and racks found in this facility [START_REF] Perović | Identification and characterization of design fires and particle emissions to be used in performance-based fire design of nuclear facilities[END_REF].

Experimental data related to cabinet fires are needed to quantify and reduce the uncertainties of the consequences of these fires for critical safety equipment [START_REF] Salvi | Analysis of historic fires to determine most frequent challenging events[END_REF]. This is especially true when fire models are not completely validated to predict complex fire propagation mechanisms and their consequences such as fire spread between adjacent electrical cabinets [START_REF]EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities: Volume 2: Detailed Methodology[END_REF]. However, few experimental data are available on this fire safety issue. Two initial studies [START_REF] Chavez | An experimental investigation of internally ignited fires in nuclear power plant control cabinets, Part I: Cabinet effects tests[END_REF]- [START_REF] Mangs | Calorimetric fire experiments on electronic cabinets[END_REF] have investigated fire spreading between adjacent electrical cabinets. The first study demonstrated that the fire did not spread from the burning open-door cabinet to the adjacent one, which was separated by an air gap of one inch (2.54 cm).

Conversely, the study by Mangs et al. [START_REF] Mangs | Calorimetric fire experiments on electronic cabinets[END_REF] highlighted that fire can spread between two adjacent cabinets located against each other (i.e., without an air gap). Poly(vinyl chloride) (PVC) cable samples located inside the adjacent cabinet ignited. Based on these outcomes, [START_REF]EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities: Volume 2: Detailed Methodology[END_REF] recommended that the fire PRA approach should assume fire spread between adjacent cabinets separated by a single metallic wall and no fire spread between adjacent cabinets if they are separated by a double wall with an air gap. Recent work conducted by Zavaleta et al. [START_REF] Zavaleta | Fire spread from an open-doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility[END_REF] confirmed that fire can spread from an open-door electrical cabinet to two adjacent closed-door cabinets when they are placed against each other without any air gap between their side walls. Otherwise, an additional work [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF] was conducted at reduced-scale to investigate the fire spread from a burning enclosure to an adjacent one, both separated by an air gap that varied in the 0-5 cm range. This study revealed that fires can spread to the adjacent cabinet up to the 5 cm wide air gap. Based on the latter experimental findings, new investigations appeared necessary to complete the understanding of fire spreading between adjacent electrical cabinets separated by an air gap. Moreover, the electrical cabinets in NPPs are commonly connected to each other by cable trays, as reported in [START_REF] Nrc | Verification and validation of selected fire models for nuclear power plant applications[END_REF]. However, the study of their impacts on fire spreading between adjacent cabinets, as recommended by Chavez [START_REF] Chavez | An experimental investigation of internally ignited fires in nuclear power plant control cabinets, Part I: Cabinet effects tests[END_REF], has not been addressed so far. Thus, to support fire safety analyses that aim at assessing the fire spread ability between separated and connected adjacent cabinets, as found in nuclear facilities, a test series of four large-scale fire tests was carried out as part of the OECD/NEA PRISME-3 project (see overview in [START_REF] Suard | Overview of the OECD PRISME 3 Project[END_REF]). The goal of this test series is especially to investigate the fire spread paths from a central open-door electrical cabinet to two adjacent closed-door electrical cabinets. The cabinets, separated by a double wall with an air gap, were connected by two overhead and two subfloor cable trays. Furthermore, the numerous cabinets present in NPPs (on the order of 500 cabinets per plant [START_REF] Worrell | Fire Probabilistic Risk Assessment and its Applications in the Nuclear Power Industry[END_REF]) can be distributed through rooms with a wide range of volumes. In addition, the ventilation conditions in the different rooms of NPPs (switchgear room, cable spreading room, main control room, turbine building…) may be either mechanically or naturally ventilated [START_REF] Nrc | Verification and validation of selected fire models for nuclear power plant applications[END_REF]. Based on these room characteristics, it was considered useful to study the impact of the room oxygen availability on the fire spread paths. To this end, two tests were conducted in open atmosphere conditions (maximum O2 availability) while the other two were performed in confined and mechanically ventilated conditions (reduced O2 availability). The fire test matrix, the test device and the related instrumentation are first presented. The results and discussion are then set out in the main part of this work. This part first deals with the global fire scenario for all the tests and comments on the related heat release rates. Next, the first fire spread path through the double wall with an air gap is addressed. The criteria leading to the occurrence of the ignitions induced by a hot wall are tackled in this section. Finally, the last two parts provide the outcomes and discussions related to the other two evidenced fire spread mechanisms through the overhead and subfloor cable trays.

Fire test description

Fire test matrix

The test device of the four adjacent cabinet tests, ACT-1 to ACT-4, devoted to the study of the fire spread paths from a central open-door electrical cabinet (CC) to two adjacent closed-door electrical cabinets (ACs), is shown in Fig. 1A. The adjacent walls of the CC and ACs were separated by a 1 cm air gap, as shown in Fig. 1B. Fig. 1A also shows two overhead cable trays that connected the three cabinets. Two subfloor cable trays, contained in the raised floor located below the cabinets, also linked the three cabinets. The test device used for the four tests (Fig. 1) was the same except the electrical cable type installed along the four cable trays. ACT-1 and ACT-3 used a "low-qualified" (LQ) PVC-based cable type while ACT-2 and ACT-4 involved a "well-qualified" (WQ) halogen-free flame retardant (HFFR) cable type. Furthermore, the two first tests, ACT-1 and ACT-2, were carried out in open atmosphere conditions, in the wide (2000 m 3 in volume) and well-ventilated SATURNE facility that contains numerous openings located at its top (Fig. 2). The test device was placed under a large-scale calorimeter. The latter is equipped with a 4.5 x 4.5 m 2 square section exhaust smoke hood that is connected to the exhaust duct of a ventilation network equipped with a dilution line, high efficiency particulate air (HEPA) filters and fans (not shown in Fig. 2). The initial volume flow rate in the exhaust duct was of 20000 m 3 /h. Otherwise, the two other tests, ACT-3 and ACT-4, were conducted in confined and mechanically ventilated conditions, in the DIVA facility. The latter contains five rooms in total (Fig. 3). Firstly, the ground floor consists of three rooms (rooms 1 to 3) of similar size (110 m 3 ) and arranged in a row separated by fire doors. Moreover, each room also provides access to a corridor (room 0 of 150 m 3 in the background of Fig. 3) through fire doors. A fifth room of about 160 m 3 is located on the first floor (room 4). The bearing walls of these rooms, made of reinforced concrete, are 0.3 m thick and 4 m high. For thermal protection, the above walls were covered with 5 cm layer of sacrificial concrete panels in all the rooms. The ceilings of all the rooms were made of four layers with concrete (30 cm), air gap (10 cm), Board Plus LTI insulated panels (1 cm) and « Monalite M1A » calcium silicate panels (1.3 cm, ρ = 720 kg/m 3 , k = 0.19 W/K/m, Cp = 960 J/kg/K). The ventilation system of the DIVA facility consists of two separate inlet and outlet networks (in blue and red in Fig. 3, respectively) which are connected to each room. The multi-rooms DIVA facility is representative of room configurations that can be found in NPPs as described in [START_REF] Nrc | Verification and validation of selected fire models for nuclear power plant applications[END_REF]. ACT-3 and ACT-4 used the rooms 1-3 (R1-R3) of the DIVA facility as illustrated in Fig. 4. Fig. 5 shows a photograph of R1 and one of R2 with the test device. The latter was installed in R2 at the centre of the north wall and the rear panels of the cabinets were located at about 1 m from this wall. The three rooms were connected by two open doorways 217 x 79 cm 2 that were located between R1/R2 and R2/R3. Concerning the ventilation network, an inlet duct was located in the upper part of R1 while an outlet duct was positioned in the upper part of both R2 and R3, as specified in Fig. 4.

The ventilation renewal rate (VRR) before ignition for the R1 to R3 volume (i.e., 330 m 3 ) was about 11 h -1 , leading to an initial volume flow rate of about 3600 m 3 /h at the inlet and 1800 m 3 /h at each of the two outlets. The flow directions at the inlet and outlets are also indicated in Fig. 4.

Table 2 summarizes the fire test matrix of this study. The main purpose of this work is to highlight, in open atmosphere and confined conditions, the fire spread paths from the CC to the ACs through the double wall with a 1 cm air gap and the four cable trays (Fig. 1). The impacts on the fire spread mechanisms of the cable type (either LQ or WQ) and of the test conditions are especially tackled in this work.

Test device 2.2.1 Central open-door cabinet

ACT-1 to ACT-4 used the same central open-door and adjacent closed-door cabinets (Fig. 1). The central cabinet (CC) is a twin-module low-voltage (400 V) control electrical cabinet that can be found in French nuclear installations and that was used in [START_REF] Coutin | Characterization of open-doors electrical cabinet fires in compartments[END_REF], [START_REF] Zavaleta | Fire spread from an open-doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility[END_REF]. This common cabinet type that is used to control, adjust and monitor the operation of machinery and systems, can also be found in many abroad NPPs such as e.g. in US NPPs [START_REF] Mcgrattan | Heat Release Rates of Electrical Enclosure Fires (HELEN-FIRE)[END_REF]. The central cabinet was implemented without door since this configuration is considered in fire safety analyses as the most critical fire scenario. The cabinet width, depth and height were 1.2, 0.6 and 2 m, respectively. The main electrical components inside the cabinet (Fig. 6) were transformers (1), terminal blocks (2), motor circuit breakers and contactors (3), relays (4), circuit breakers ( 5), trunkings ( 6) and electrical cables. The ignition inside the cabinet was performed with a propane burner which was located at the bottom of the CC (Fig. 7). This burner, composed of a steel pipe (1) with small holes and a spark system (2), provided a fire power of 10 kW for a duration of 5 min for all the tests.

Fig. 6: central electrical cabinet without door used for ACT-1 to ACT-4.

(1)

(3)

Closed-door adjacent cabinets

The two closed-door adjacent electrical cabinets (ACs) were 0.6 m wide, 0.6 m deep and 2 m high (Fig. 1A). The interiors of the right-and left-hand adjacent cabinet (RHAC and LHAC, respectively) had the same content, composed of four types of targets, as specified in Table 3. As an example, Fig. 8 shows the interior of the RHAC. These target types contained sets of electrical components that are identical to those located close to the side walls of the CC (Fig. 6). In addition, as configured in the CC, these targets were set at a distance of a few cm from the AC side walls and they were all connected to each other by cable wires (see for example Fig. 8C). Finally, the closed-door ACs were naturally ventilated. For this purpose, their door was equipped with two metallic 0.2 m x 0.2 m square ventilation grids (Fig. 1).

Overhead and subfloor cable trays

Each of the two overhead and two subfloor cable trays contained twenty samples of the LQ cable (2.8 cm in diameter) and twenty-eight of the WQ cable (2 cm in diameter) for ACT-1/ACT-3 and ACT-2/ACT-4, respectively. With this loading, at least one tight layer of cables completely filling the trays was obtained, as illustrated for both the overhead and subfloor cable trays in Fig. 9.

Connections between the adjacent cabinets and the cable trays

Fig. 8A shows the cable bundle coming from the overhead cable trays through the upper cable passage located in the ceiling of the adjacent cabinet (AC). Such a cable bundle connected each of the two ACs to the central open-door cabinet (CC) through the overhead cable trays for all the tests. Fig. 8A also

(2) (1)
A B

shows cable samples coming from the subfloor cable trays through the slot-shape cable passage that equipped each of the metallic floor of the two ACs. These cable samples connected the bottom of the CC (Fig. 7) to the two ACs through the subfloor cable tray for all the tests.

Raised floor configuration

For ACT-1 and ACT-2, each of the two raised floor ends was nearly covered by a corner-shape metallic plate as seen in Fig. 10A, resulting in a small opening of 0.03 m 2 located at their lower part. In contrast, for ACT-3 and ACT-4, the corner-shape plates were removed, leading to a raised floor with open ends (Fig. 10B). This was the only modification between the test device of ACT-1/ACT-2 and that of ACT-3/ACT-4 (besides the cable type along the cable trays that also changed according to the test, as previously specified). This allowed a study of the impact of the raised floor configuration (either nearly closed or open) on fire spread along the subfloor cable trays.

Instrumentation

First, for each adjacent cabinet (AC), twelve K-type thermocouples (TCs) were placed in or very close to the targets, as shown in Fig. 11. Nine TCs were inserted in targets 1 and 3 (PVC trunkings) and measured gas temperatures close, respectively, to the electric cables and wires contained inside. The last three TCs were placed very close to target 2 (terminal blocks) and measured gas temperatures. Two additional TCs were located both at their upper and lower cable passages, as further shown in sections 3.3 and 3.4. All the thermocouples contained in the left-hand adjacent cabinet were placed in identical manner. Each AC also hosted two Gardon-type heat flux sensors for measuring the incident total heat flux at 30 cm from the hot side walls and at 50 and 150 cm above the floor (see Fig. 8). The goal of all the above measurements was to detect the potential ignition of a target and its location, as it will be . Furthermore, each of the four cable trays was equipped with eleven K-type TCs that were placed just above the cables and set 30 cm apart, as depicted in Fig. 9. Several cameras were used for these tests. Some of them provided an overview of the test device during the fire tests while the others aimed at observing the fires that occurred in the ACs. Finally, carbon dioxide (CO2), carbon monoxide (CO) and oxygen (O2) concentrations, gas temperatures, pressures and volume flow rates were measured in the exhaust ventilation duct of the large-scale calorimeter of the SATURNE facility, as well as in the rooms and ventilation network of the DIVA facility. These measurements were especially used in this study to assess the heat release rate (HRR) of the four fire tests. Finally, the data acquisition system for the entire series of measurements had a sampling time set at 1 s.

Results and discussion

This part first provides the assessment of the HRR and a brief description of the global fire scenario for all the tests. It next focuses on the three highlighted fire propagation paths through the double wall with a 1 cm air gap, the overhead and subfloor cable trays.

Heat release rate assessment and global fire scenario

The HRR is the main parameter for assessing the consequences of a fire, as emphasized by Babrauskas et al. [START_REF] Babrauskas | Heat release rate: the single most important variable in fire hazard[END_REF], and for most fire model applications [START_REF]Nuclear Power Plant Fire Modeling Analysis Guidelines[END_REF]. The HRR was assessed from the calorimetric methods [START_REF] Tewarson | Generation of Heat and Chemical Compound in Fires[END_REF]- [START_REF] Brohez | The measurement of heat release from oxygen consumption in sooty fires[END_REF] that were adapted by Pretrel et al. [START_REF] Pretrel | Experimental determination of fire heat release rate with OC and CDG calorimetry for ventilated compartments fire scenario[END_REF] for confined and mechanically-ventilated rooms. More details on the application of these methods for conditions similar to this work can be found in [START_REF] Zavaleta | Fire spread from an open-doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility[END_REF]. Fig. 13 provides the HRR for ACT-1 to ACT-4 over 20 min. The first and main growth of the HRR corresponds to the progressive vertical fire spread along the open-door electrical cabinet from its bottom where it was initiated (Fig. 7B), up to the overhead cable trays as illustrated in Fig. 14 e.g. for ACT-1. Note that Fig. 13 shows satisfactory repeatability of the growth stages of the four cabinet fires over the first nine minutes. Otherwise, this figure next reveals that the cabinet fire growth stages in confined conditions (ACT-3 and ACT-4) are reduced compared to those obtained in open conditions (ACT-1 and ACT-2). Oxygen concentrations indeed decrease in confined conditions as fire grows, as illustrated in Fig. 16 for ACT-4 that provides the O2 concentrations measured at low (0.7 m high), mid (2.2 m high) and high (3.3 m high) parts in the south-east corner of the fire room (Fig. 15). In addition, for the whole tests, several ignitions occurred in the ACs over the first 20 minutes, as fully described in section 3.2. Furthermore, fire spread along the overhead cable trays and clearly later along the subfloor cable trays. However, these outcomes were only obtained when the LQ cable type was used (i.e. for ACT-1 and ACT-3), as detailed in sections 3.3 and 3.4 and illustrated in Fig. 17, which gives the HRRs over 100 min. This figure indeed shows that after the first peak, corresponding mainly to the cabinet fire, the HRRs were significantly higher for ACT-1 and ACT-3 than for ACT-2 and ACT-4, caused by the cable tray fires that only developed for the first two tests. The global fire scenario e.g., for ACT-1 can be viewed with the uploadable movie file "Global_fire_scenario_ACT-1.wmv". Fig. 17: heat release rate over 0 s ≤ t ≤ 6000 s for ACT-1 to ACT-4.

Fire spread path through the double wall with a 1 cm air gap

The first part of this section deals with the ignitions induced by a hot wall and the resulting fire stages that were observed in the adjacent cabinets (ACs) for the four tests. The second part proposes a discussion on fire spread ability through the double wall with a 1 cm air gap based on the outcomes of this work and those obtained from previous works that were earlier mentioned.

Ignitions induced by a hot wall resulting in fires in the ACs

This part first discusses the ignitions and resulting fire stages related to the side wall paintwork and next those regarding the targets.

Side wall paintwork

Five ignitions of the side wall paintwork were identified in the ACs for all the tests from video analyses, as specified in Table 4. These ignitions happened over the first 20 minutes when the AC side wall temperature measured near the ignited paintwork location exceeded 500 °C, as exemplified in Fig. 18 for ACT-1 (LHAC) and ACT-3 (RHAC). The ignitions were followed by short fires that extinguished fast and did not spread to the targets. Their duration was around one minute except the last one (3.5 minutes), as mentioned in Table 4.

Table 4: paintwork ignitions identified in the adjacent cabinets over the first twenty minutes and the resulting fire durations (ACT-1 to ACT-4).

Paintwork ignition

Related

Targets

This section first discusses how the target ignitions and the resulting fire stages were identified. The second part addresses the temperature and heat flux criteria leading to the target ignition.

Identification of the target ignitions and resulting fires

Four target ignitions were first identified from video analyses in the RHAC for all the tests, as specified in Table 5. These ignitions occurred only in the RHAC over the first 20 minutes. The latter table also indicates that the target ignitions especially involved the target 2 type (terminal blocks) and potentially the cable wires that connected this target type and target 1 and 3 types (Fig. 8C). Table 5 finally reveals that the target ignitions and resulting fires occurred for tests conducted both in open atmosphere and confined conditions. Video analyses also showed that after the ignition of a target at a given location, fire spread to targets located in close proximity, leading to long fires from 30 to 70 min, as summarized in Table 5. Target fires were therefore significantly longer than the paintwork fire stages. One example of target ignition and the subsequent fire stage can be observed using the uploadable movie file "Target_ignition_ACT-2.wmv". Measurements of the temperature in the ignited target and of the heat flux nearby can also confirm the target ignition and the resulting fire. For illustration, Fig. 19 shows target temperatures and heat flux measured at the lower part of the RHAC for ACT-1. The sudden and significant increase of the temperature measurement, T2_90cm, beyond 500 °C confirms the first target ignition (target-I1) that occurred in target 2 (T2) at 18 min and at a height of about 90 cm (Table 5). Heskestad [START_REF] Heskestad | Flame Heights of Fuel Arrays with Combustion in Depth[END_REF] indeed specified that a temperature measurement above 500 °C may correspond to the presence of flames at the considered measurement location. Fire next spread downwards to target 3 (T3) located nearby and about 50 cm up, as corroborated by the strong increase of both the related target temperature, T3_50cm, and the close heat flux, HF_50cm.

A B

Target ignition criteria

All the target ignitions only occurred in the RHAC when the temperature of its side wall measured near the ignited target exceeded 600 °C, as exemplified in Fig. 20 for ACT-1 and ACT-2. Note that the above ignition criterion was reached for targets that were set a few cm from the RHAC adjacent wall, as previously mentioned. In contrast, targets did not ignite in the LHAC since the maximum temperatures of its adjacent wall did not exceed 600 °C. The temperatures of the left-hand side wall of the central cabinet (LHCC) were indeed significantly lower than those of its right-hand side wall (RHCC). This is exemplified for ACT-1 in Fig. 21 for the CC side wall temperatures measured 90 and 160 cm up. The maximum temperatures of the LHCC indeed hardly reached values of 600 °C while those for the RHCC were higher than 700 °C. Such differences could be mainly attributed to the different content of electrical components present in the left and right-hand modules of the CC, as shown in Fig. 6. Indeed, their combustion, during the fully developed central open-door cabinet fire, could lead to higher flame temperatures along the right-hand side wall than along its left-hand one. Furthermore, the incident heat flux from the side wall to the close targets, 𝑞̇ " , can be assessed as follows [START_REF] Drysdale | An introduction to fire dynamics[END_REF]:

𝑞̇ " = 𝐹 𝜀𝜎 𝑇 ( 1
)
Where 𝐹 is the view factor for a very small area of the target, 𝑑𝐴 , to the side wall area, 𝐴 (-). Given the closeness of the targets to the side wall, 𝐹 is assumed equal to 1. 𝜀 is the side wall emissivity (-), 𝜎 the Stephan-Boltzmann constant (5.67.10 -8 W.m -2 .K -4 ) and 𝑇 the side wall temperature (K). 𝑞̇ " is evaluated according to Eq. ( 1) considering a temperature of 600 °C over a side wall region 𝐴 facing the small area of the target 𝑑𝐴 . In addition, 𝜀 is assumed to be 0.8, as shown in [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF]- [START_REF] Sadiq | Determination of Steel Emissivity for the Temperature Prediction of Structural Steel Members in Fire[END_REF], for similar steel walls when the latter are heated up to around 600 °C. This therefore gives 𝑞̇ " of about 26 kW/m 2 . Accordingly, the ignition of targets composed of terminal blocks can be expected for an incident heat flux higher than 26 kW/m 2 . Such a level is consistent with the critical ignition heat flux (31 ± 3 kW/m 2 ) that was measured in [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF] for the same type of terminal blocks.

Discussion

As previously stated, [START_REF]EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities: Volume 2: Detailed Methodology[END_REF] recommended for the fire PRA approach to assume no fire propagation between adjacent cabinets if they are separated by a double wall with an air gap. This recommendation was based on previous investigation [START_REF] Chavez | An experimental investigation of internally ignited fires in nuclear power plant control cabinets, Part I: Cabinet effects tests[END_REF] that showed no fire spread between the burning open-door cabinet and the adjacent one that were separated by an air gap of one inch (2.54 cm). However, the current study highlighted fire spread for the double wall with a 1 cm air gap both in open atmosphere and confined conditions. Recent work [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF] also showed that fire can spread between adjacent enclosures separated by a double wall with a 5 cm air gap and for a target type composed of the same terminal blocks as those considered in the current study. Accordingly, the possibility of fire spread between adjacent cabinets separated by a double wall with an air gap cannot be ruled out.

Study [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF] also demonstrated that the increase of the air gap in the 1-5 cm range can delay the fire spread (when terminal blocks are used as targets), given the air flow increase between the side walls of the adjacent cabinets. This slowed down or even reduced the heating by the cabinet fire of the side walls. The above work also revealed that the air gap rise can prevent the ignition of other target types than terminal blocks, if the related side wall temperature and heat flux criteria are not reached Accordingly, the fire spread possibility does not depend only on the air gap thickness, but also on the electrical

A B

component type located in the adjacent cabinet in the proximity of its side wall. In addition, the characteristics of the fire source, such as its duration and power, are also parameters to be considered [START_REF] Zavaleta | Fire spread from an open-doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility[END_REF]- [START_REF] Zavaleta | Electrical component ignition in a closed enclosure adjacent to a controlled fire[END_REF] since they impact the adjacent cabinet side wall temperature and incident heat flux that can trigger the target ignitions. Note also that the fire spread to the adjacent cabinet can result from the ignition of the side wall paintwork, as earlier shown in this work, even if the resulting fire extinguished fast. The fire spread assumption between adjacent cabinets separated by a double wall with an air gap could therefore rely on the achievement of the side wall temperature or incident heat flux criteria such as those determined in this study for the ignitions of the side wall paintwork or terminal blocks. These electrical components are commonly found in low voltage electrical cabinets.

Fire spread path through the overhead cable trays

This section first comments on the fire spread through the overhead cable trays and then the potential fire spread to the two adjacent cabinets from these trays.

Fire spread along the overhead cable trays

First, the open-door cabinet fire reached the overhead cable trays for all tests, as illustrated in Fig. 14. However, fire only spread along these trays when the "low-qualified" (LQ) cable was used (i.e. for ACT-1 and ACT-3), as illustrated in Fig. 22 for ACT-1. This spreading is confirmed by the temperature measurements as illustrated e.g. by those performed along the left-hand part of the upper overhead cable tray (tray 4 as seen in Fig. 12) for both ACT-1 and ACT-3, as seen in Fig. 23. All these measurements, except one located at the tray end for ACT-1, indeed show steep and significant increases clearly over 500 °C. As previously commented, the attaining of such temperature values at a given location indeed means that fire reached this position. In contrast, ACT-2 and ACT-4, which used the WQ cable, showed that the overhead cable trays were not ignited. Note also that fire spread along the overhead cable trays filled with the LQ cable type for both open atmosphere and confined conditions. However, for confined ACT-3, the cable trays ignited later (16 min) than for ACT-1 (9 min 30 s) and 6 min 30 s after the cabinet fire peak. The O2 concentration measured near the overhead cable trays (3.3 m up) in confined conditions dropped to a minimum value of 7.5 Vol% at the cabinet fire peak (Fig. 24), thus preventing their ignition. The cable tray ignition for ACT-3 occurred when the above O2 concentration next increased to a value of 12 Vol% (see Fig. 24) due to the air renewal in the mechanically ventilated fire room.

Fire spread to the adjacent cabinets through the overhead cable trays

As earlier described, the ceiling of each AC was equipped with one cable passage where a cable bundle was inserted, as depicted in Fig. 25A e.g. for the RHAC. This figure also shows the thermocouples located at the upper cable passages, TOP_P1 and TOP_P2, and those positioned at the tops of targets 1 and 3 (190 cm high), T1_190cm and T3_190cm, respectively. Fig. 25B provides the time evolutions of these measurements for ACT-3. The latter figure first reveals maximum temperatures at the upper cable passage (TOP_P2), nearly 500 °C at about 4000 s, showing the proximity of flames at this location in accordance with the Heskestad criterion [START_REF] Salvi | Analysis of historic fires to determine most frequent challenging events[END_REF], as earlier commented. At the same time, the temperature measurements, T1_190cm and T3_190cm, were around 300 °C (Fig. 25B). This shows that fire at the upper cable passage could only propagate from the overhead cable tray fire. Fire can therefore spread to the ACs from overhead cable trays through the upper cable passages.

A B

Fig. 25: temperatures measured at the top of the right-hand adjacent cabinet. A. Thermocouples, T1_190cm and T3_190cm, located at the tops of targets 1 and 3, respectively, and those, TOP_1 and TOP_2, located at the upper cable passage. B. Times evolutions of the temperatures for ACT-3.

3.4

Fire spread path through the subfloor cable trays (raised floor)

This section first discusses the fire spread along the subfloor cable trays and next the potential fire spread to the two adjacent cabinets from these trays.

Fire spread along the subfloor cable trays

The subfloor cable trays, located below the central open-door cabinet (CC), ignited at 32 and 30 min in ACT-1 and ACT-3, respectively. Fire next spread along these two cable trays only for the two tests that used the LQ cable type. Fig. 26 shows for instance the temperatures measured along the upper subfloor cable tray (tray 2 as seen in Fig. 12) for ACT-1. This figure reveals that the fire spread along the left-hand part of this tray and reached its end at about 80 min (see mark [START_REF] Thomson | Chapter 2, Fire Risk Assessment, Fire Hazards in Industry[END_REF] in Fig. 26A). Indeed, the corresponding temperature measurement L_150cm exceeded the value of 500 °C from the above time, showing the presence of flames at this location. In contrast, over the same time period, Fig. 26B reveals that the fire did not spread beyond the 60 cm location on the right-hand part. Fire spread much later over all this portion of the upper subfloor cable tray, as testified by the temperature measurements that exceeded 500 °C first over the first 30 cm from 120 min (see mark [START_REF] Schneider | introduction to fire safety in nuclear power plants[END_REF] in Fig. 26B) and next over the other part from 175 min (see mark (3)). A similar fire spread scenario was observed for the lower subfloor cable tray (tray 1 as seen in Fig. 12). Consequently, in ACT-1, the fire first spread along the left-hand part of the subfloor cable trays and next along the right-hand part. Fig. 27 shows for example the temperatures measured along the upper subfloor cable tray for ACT-3. This figure shows that the fire spread quite symmetrically from the centre of this tray to both the left and right-hand ends, reached at 55 and 50 min, respectively. The corresponding temperature measurements, L_150cm and R_150cm, were higher than 500 °C from 55 min (see mark [START_REF] Schneider | introduction to fire safety in nuclear power plants[END_REF] in Fig. 27A) and 50 min (see mark [START_REF] Thomson | Chapter 2, Fire Risk Assessment, Fire Hazards in Industry[END_REF] in Fig. 27B), respectively, showing the presence of flames at these locations.

As previously indicated, ACT-1 and ACT-3 used the same raised floor except its ends, which were nearly closed for the first and open for the latter (Fig. 10). Thus, a more naturally ventilated raised floor in ACT-3 led to a symmetrical and faster fire spread than the asymmetric fire spread observed for ACT-1 along the nearly confined raised floor.

3.4.2 Fire spread to the adjacent cabinets through the subfloor cable trays Fig. 28A shows in the lower part of the RHAC the thermocouples located at the bottom of target 2 (T2_20cm) and at the lower cable passage (LOW_P1 and LOW_P2). Fig. 28B-C shows for ACT-1 and ACT-3, respectively, the above temperature measurements and also those performed below the RHAC along the right-hand part of cable tray at 60 cm and 90 cm from its centre (R_60cm and R_90cm, respectively). For ACT-1, Fig. 28B first illustrates that the temperature measurements, LOW_P1, LOW_P2 and T2_20cm, suddenly increased at 12000 s (3 h 20 min); shortly after that those for R_60cm and R_90cm were higher than 500 °C (showing fire at these locations). This provides evidence for fire spreading in the RHAC from the subfloor cable trays through the lower cable passage. This fire stage started at 3 h 20 min. Moreover, for ACT-3, Fig. 28C shows that temperature measurements, LOW_P2 and T2_20cm, suddenly increased after and before respectively the significant rises of the temperature measurements, R_60cm and R_90cm. Thus, the lower cable passage and the bottom of target 2 both ignited (at 33 and 34 min, respectively) when fire reached the cable tray portion beneath the RHAC. This provides evidence that fire spread to the bottom part of the RHAC from the subfloor cable trays. This led to the development of a long fire of about 130 min in the RHAC for ACT-3 which involved the targets installed at its lower part and those which were relocated at its bottom. A similar fire spread scenario occurred in the LHAC. The lower cable passage and the bottom of the targets ignited at 37 min and 38 min, respectively, when flames reached the left-hand part of cable tray located beneath (i.e. between 60 cm and 90 cm from its centre). Afterwards, a long-lasting fire of about 100 min occurred in this cabinet. Fire can therefore spread from the CC to ACs through the subfloor cable trays if the LQ cables are used. Moreover, this fire spread mechanism in the ACs can occur much earlier if the ends of the raised floor are open (ACT-3) instead of being nearly closed (ACT-1). The more naturally ventilated subfloor cable tray fire in ACT-3 compared to ACT-1 resulted in a faster fire spread along the subfloor cable trays. Moreover, this fire propagation mechanism occurred in both LHAC and RHAC for ACT-3, while it only concerned the RHAC for ACT-1. The resulting fires in the two ACs for the first test were also noticeably longer (more than 100 min).

B C

Conclusion

The main objective of this work was to study, in open atmosphere and confined conditions, fire spreading paths between a central open-door electrical cabinet (CC) and two adjacent closed-door cabinets (ACs). The cabinets, separated by a double wall with a 1 cm air gap, were connected by two overhead and two subfloor cable trays. These last ones were filled with either a "low" or a "wellqualified" (LQ or WQ) cable type that can be found in NPPs. ACT-1 and ACT-2 were conducted in open atmosphere conditions and ACT-3 and ACT-4 in confined and mechanically ventilated conditions. In addition, ACT-1 and ACT-3 used the LQ cable type while ACT-2 and ACT-4 used the WQ cable type.

The global fire scenario for all the tests was first presented as well as the heat release rate that was assessed for the four tests. The tests especially highlighted three fire spreading paths between the CC and the ACs. Regarding the first one through the double wall with a 1 cm air gap, several ignitions of the wall paintwork occurred in the ACs as soon as the side wall temperature near the ignited location exceeded 500 °C. These ignitions were followed by short fire events. Several ignitions of electrical components (used as targets) also happened in the right-hand adjacent cabinet (RHAC). These ignitions were triggered when the side wall temperature near the ignited target and the assessed incident heat flux to the target were higher than 600 °C and 26 kW/m 2 , respectively. These two target ignition criteria were assessed for the target type composed of terminal blocks and potentially the connected wires, both located a few cm from the side wall. The target ignitions that led to long fires in the RHAC occurred for the tests conducted both in open atmosphere and confined conditions. Furthermore, the second and third fire spread paths through the overhead and the subfloor cable trays, respectively, were highlighted if the LQ cable type was used (i.e. for ACT-1 and ACT-3). Regarding the path through the overhead cable trays, fire propagated to one of the two ACs through the upper cable passage for ACT-3. Moreover, the third fire spreading path through the subfloor cable trays was highlighted for both ACT-1 and ACT-3. However, it occurred much earlier for ACT-3 in both LHAC and RHAC (within 40 min) than for ACT-1 in only the RHAC (from 3 h 20 min). Given that the ends of the raised floor were open in ACT-3 and nearly closed in ACT-1, the more naturally ventilated raised floor led to a faster fire spreading along the subfloor cable trays in the first test. The resulting fires in the two ACs for ACT-3 were also clearly longer (more than 100 min) than that obtained in the RHAC for ACT-1. Conversely, for the WQ cable type (i.e., for ACT-2 and ACT-4), fire did not spread along the overhead and subfloor cable trays. This work highlighted three different fire spread paths, for both open and confined environment: propagation through a double wall with an air gap and propagation through overhead and subfloor cable trays. These experimental findings, obtained from realistic cabinet configurations, should provide updated insights for fire safety analyses conducted in NPPs and also in many other industrial sectors. Thus, an open-door vertical enclosure (that can lead a full fire development) and the use of lowqualified cables along the cable trays could increase the fire spread likelihood between the adjacent cabinets, via the double wall and the cable trays, respectively. Otherwise, the presence close to the cabinet side walls of least flammable electrical components as possible and the use of well-qualified cables along the cable trays, could reduce the fire spread hazard via the double wall and the cable trays, respectively.

Acknowledgement

This work was performed by IRSN in the frame of the OECD/NEA PRISME-3 Project with the support of the following international partners: ENGIE and Bel V (Belgium), VTT (Finland), DGA and EDF (France), GRS and iBMB (Germany), CRIEPI and NRA (Japan), KAERI (Korea), ONR (United Kingdom) and NRC (United States of America). The authors also thank the technical team of the fire test laboratory for its assistance in carrying out all the experiments.

Fig. 1 :

 1 Fig. 1: test device of the four ACT-1 to ACT-4. A. Overall view. B. A 1 cm air gap separating the adjacent cabinets.

Fig. 2 :

 2 Fig. 2: large-scale calorimeter of the SATURNE facility. A. Test device (1) under the large-scale hood (2) used for ACT-1 and ACT-2. B. Large-scale calorimeter of the SATURNE facility with the hood (2) connected to the exhaust ventilation duct (3).

Fig. 3 :

 3 Fig. 3: perspective view of the DIVA facility.

Fig. 4 :

 4 Fig. 4: rooms 1-3 (R1-R3) of the DIVA facility and the ventilation ducts as configured for ACT-3 and ACT-4. The white arrows indicate the flow directions at the inlet and outlets.

Fig. 5 :

 5 Fig. 5: room 1 (left) and room 2 (right) of the DIVA facility as configured for ACT-3 and ACT-4.

Fig. 7 :

 7 Fig. 7: enlarged view of the propane pipe (1) and spark system (2) located at the bottom of the central opendoor electrical cabinet. A. Before the ignition. B. A few seconds after the ignition starting.

Fig. 8 :Fig. 9 :

 89 Fig. 8: interior of the right-hand adjacent cabinet. A. Overview. B and C. Enlarged views of the targets and sensors in the lower and upper parts, respectively. HFS, heat flux sensor, TC, thermocouples. T1 to T4, targets 1 to 4. T1: target 1 (PVC trunking with cable samples); T2: target 2 (sets of terminal blocks); T3: target 3 (PVC trunking with cable wire samples); T4: target 4 (circuit breakers, relays, …).

Fig. 10 :

 10 Fig. 10: raised floor ends. A. ACT-1 and ACT-2. B. ACT-3 and ACT-4.

  Small opening (0.03 m 2 ) at the bottom of the two raised floor ends further discussed. Fig.12is a diagram of the test device showing the TC's implementation along the side walls and the four cable trays. Nine K-type TCs were therefore fixed against the side walls of both the left-and right-hand adjacent cabinets (LHAC and RHAC, respectively) along with nine against both the left-and right-hand side walls of the central cabinet (LHCC and RHCC, respectively)

Fig. 11 :

 11 Fig.11: locations of the target temperature measurements in the right-hand adjacent cabinet. Six thermocouples (TCs), T1_20cm to T1_190cm, inserted in target 1 (T1), three TCs, T2_20cm, T2_90cm and T2_160 cm, placed very close to target 2 (T2) and three last ones, T3_50cm, T3_130cm and T3_190cm, located in target 3 (T3). T1_130cm TC is not shown in the above pictures.

Fig. 12 :

 12 Fig. 12: schematic of the test device showing the thermocouples fixed against the side walls of the leftand right-hand adjacent cabinets (LHAC and RHAC, respectively) and also against the left-and righthand side walls of the central cabinet (LHCC and RHCC, respectively) and those placed along the four cable trays. Trays (1) and (2) for the lower and upper subfloor cable trays, respectively. Trays (3) and (4) for the lower and upper overhead cable trays, respectively.

Fig. 14 :

 14 Fig. 14: fire spread along the cabinet up to the overhead cable trays (e.g. for ACT-1).

Fig. 15 :

 15 Fig. 15: locations of the oxygen concentration measurements performed in the fire room.

Fig. 16 :

 16 Fig. 16: oxygen concentrations measured in the fire room for ACT-4.

Fig. 18 :

 18 Fig. 18: side wall temperatures for 0 s ≤ t ≤ 1200 s. A. ACT-1 (LHAC). B. ACT-3 (RHAC).

Fig. 19 :

 19 Fig. 19: target temperatures and heat flux measured at the lower part of the right-hand adjacent cabinet for ACT-1. A. Thermocouples, T2_90cm and T3_50cm, located in targets 2 (T2) and 3 (T3), respectively, and the heat flux sensor, HFS_50cm. B. Time evolutions of the measured temperatures and heat flux.

Fig. 20 :Fig. 21 :

 2021 Fig. 20: side wall temperatures for the RHAC (0 s ≤ t ≤ 1200 s). A. ACT-1. B. ACT-2.

Fig. 22 :Fig. 23 :

 2223 Fig. 22: fire spread along the overhead cable trays (e.g. for ACT-1). A. fire involving the cable tray central part as the cabinet fire declined. B. Fire reaching the cable tray ends.A B

Fig. 24 :

 24 Fig. 24: oxygen concentrations measured in the fire room for ACT-3.

Fig. 26 :

 26 Fig.26: temperatures measured along the upper subfloor cable tray (tray 2 as seen in Fig.12) for ACT-1.A. Left-hand part for 0 s ≤ t ≤ 7000 s. B. Right-hand part for 0 s ≤ t ≤ 16000 s.

Fig. 27 :Fig. 28 :

 2728 Fig. 27: Temperatures measured along the upper subfloor cable tray (tray 2 as seen in Fig. 12) for 0 s ≤ t ≤ 4000 s and for ACT-3. A. Left-hand part. B. Right-hand part.

Table 1 :

 1 main characteristics of the electric cables used for ACT-1 to ACT-4.

	Cable type	Related test ID	Cable specification (diameter, weight)	Material composition	Supplier reference	Cable reaction to fire (IEC and EN standard tests)
	LQ cable	ACT-1 and ACT-3	5x25 mm 2 power cable (2.8 cm, 1.75 kg/m)	PVC, PE, Phthalate, CaCO3	NYM-J 5x25 mm 2 RM GRAU	IEC/EN 60332-1-2 (EN 50575-Eca)
	WQ cable	ACT-2 and ACT-4	12x1.5 mm 2 control cable (2 cm, 0.70 kg/m)	EVA, PE, ATH	NU-SHX(ST)HX 1kV	IEC/EN 60332-1-2 IEC/EN 60332-3-22, -23, -24 IEC/EN 61034-2
						IEC/EN 60754-2

Abbreviation. ACT, adjacent cabinet test; ATH, alumina trihydrate; CaCO3, Calcium carbonate; EN, European standards; EVA, ethylene-vinyl acetate; IEC, International Electrotechnical Commission; LQ, "low-qualified"; PE, polyethylene; PVC, poly(vinyl chloride); WQ, "well-qualified".

Table 2 :

 2 fire test matrix.

	Test ID	Conditions	Cable type
	ACT-1	Open atmosphere	LQ cable
	ACT-2	Open atmosphere	WQ cable
	ACT-3	Confined and mechanically-ventilated	LQ cable
	ACT-4	Confined and mechanically-ventilated	WQ cable

Abbreviations: ACT, adjacent cabinet test; LQ, "low-qualified"; VRR, ventilation renewal rate; WQ, "well-qualified".

Table 3 :

 3 Targets placed close to the side walls of the two ACs.

	Target ID for the RHAC and LHAC	Target specification
	1	2 m long PVC trunking filled with 10 samples of a 19x1.5 mm 2 HFFR cable type.
	2	Four sets of 50 terminal blocks 4/6.
	3	2 m long PVC trunking filled with about 190 samples of a 1.5 mm 2 HFFR wire type.
		2 circuit breakers IC60 2 x 1A, 50 terminal blocks 6/8, 1 dispatcher 40 A BI,
	4	4 relays 48 VDC with its base, 2 motor-protective circuit breakers and 50
		terminal blocks 4/6.

Abbreviations: HFFR, halogen-free flame retardant; LHAC, left-hand adjacent cabinet; PVC, Poly(vinyl chloride); RHAC, right-hand adjacent cabinet.

Table 5 :

 5

	Target ignition	Related test ID	Ignition time (min)	Location	Resulting fire duration (min)
	Target-I1	ACT-1	18	Target 2 (terminal blocks) about 90 cm up	70
	Target-I2	ACT-1	19	Target 2 about 150 cm up
	Target-I3	ACT-2	14	Target 2 over 150 cm up	69
	Target-I4	ACT-4	15	Target 2 over 150 cm up	30

target ignitions identified in the right-hand adjacent cabinet over the first twenty minutes and the resulting fire durations (ACT-1 to ACT-4).

Abbreviations: ACT, adjacent cabinet test; I, ignition.