NIST Technical Note 1804 

Thermal Exposure Sensor for Fire 

Fighters- Full-Scale Performance 

Experiments 

Atul Deshmukh 

John G. Casali 

Jeff A. Lancaster 

Nelson P. Bryner 

Roy A. McLane 

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NIST Technical Note 1804 

Thermal Exposure Sensor for Fire 

Fighters- Full-Scale Performance 

Experiments 

Atul Deshmukh 

John G. Casali 

Jeff A. Lancaster 

Auditory Systems Laboratory 

Grado Department of Industrial and Systems Engineering 

Virginia Polytechnic Institute and State University 

Nelson P. Bryner 

Roy A. McLane 

Fire Research Division 

Engineering Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1804 

July 2016 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Director 
 

 

 

 

Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1804 

Natl. Inst. Stand. Technol. Tech. Note 1804, 61 pages (July 2016) 

CODEN: NTNOEF 

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Thermal Exposure Sensor for Fire Fighters- Full-Scale
 

Performance Experiments
 

ABSTRACT 

During structural fire fighting suppression operations, fire fighters wear protective gear to 

insulate them from the high temperature environment including hot combustion gases, burning 

surfaces, and thermal radiation. Current turnout gear insulates the fire fighter to such an extent, 

basically encapsulating his/her entire body that it is more difficult for each individual fire fighter 

to understand how hazardous or hot the thermal environment is. A fire fighter’s body is usually 

covered with protective gear during search and rescue operations. Therefore, the natural heatsensing mechanism of the body is incapable of sensing the ambient temperature, possibly putting 

firefighters at risk. A thermal sensing device that attaches to the visor of the head gear is 

designed to restore situational awareness of the firefighter by showing varying heat intensity 

through different colored warning indicators in the firefighter’s line of sight. Human factors 

evaluation of the performance of the warnings in the thermal sensing device was conducted in 

laboratory-scale (i.e., climatic chamber experiments) and in full-scale (i.e. fire experiments in 

ISO room) environments. While a previous report discussed the laboratory-scale experiments, 

this report describes the full-scale fire exposure experiments. The evaluation involved tracking 

the performance of multiple thermal sensors within a standard room during live fire tests. 

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LIST OF ACRONYMS
 

a Ampere 

ANSI American National Standards Institute 

ASTM American Society for Testing and Materials 

A/D Analog-to-Digital 

Al Alumel 

BFRL Building Fire Research Code 

BTU/ft3 BTU per cubic feet 

cm Centimeter 

Cr Chromel o

C Degrees Centigrade 

DAQ Data Acquisition System 

DV Digital Video 

Exp # Experiment Number 

ft foot/feet o

F Degrees Fahrenheit 

FP Facepiece 

FEE Fire Equipment Evaluator 

FT Front 

Ft3/min Cubic feet per minute 

gal/min Gallon per minute 

Hg Mercury 

Hz Hertz 

HRR Heat release rate 

kHz Kilohertz 

in Inch 

IE Inside 

ISO International Standards Organization 

kW Kilowatts 

kJ/L Kilojoules per liter 

NFPA National Fire Protection Association 

NG Natural Gas 

Ni Nickel 

NIST National Institute of Standards and Technology 

L/s Liters per second 

L/min Liters per minutes 

min Minute 

m Meter 

mm Millimeter 

m/s Meters per second 

mV Milli-volt 

mAh Milli Amperes hour 

MW Megawatts 

M # Mask number 

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MJ/kg Mega joules per kilogram 

MIDAS MIDAS computerized data collection system 

ON Power on the device 

OFF Power off the device 

Pa Pascal 

Rep Repetition 

ROM Read Only Memory 

RP Radiant Panel 

RR Rear 

RTD Resistance-Temperature Device 

s Second 

SO Static Oven 

TC Thermocouple 

TC # Thermocouple number 

TI Temperature Inside 

TO Temperature Outside 

TSU Thermal Sensing Unit 

UBC Uniform Building Code 

V Volt 

% Percent 

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1.0 INTRODUCTION 

Firefighters and first responders wear protective gear to insulate them from high 

temperature conditions including hot combustion gases, burning surfaces, and thermal radiation. 

While it is critical to protect fire fighters from adverse fire conditions, it is also important that 

fire fighters be able to continuously assess the fire environment in which they are working. A 

rapid increase in temperature may alert a fire team to worsening conditions or a cooling of the 

environment may indicate successful suppression. Being able to constantly assess their 

environment allows fire fighters to work more safely and more effectively. Current turnout gear, 

including boots, pants, coat, hood, helmet, and gloves, effectively insulates a fire fighter from 

their environment. This gear encapsulates their entire body and that makes it more difficult for 

fire fighters to sense or understand how hot or intense the conditions are that envelop them. A 

smoke filled room prevents a fire fighter from visually evaluating their environment. Before the 

current personal protective equipment was widely available, fire fighters often utilized exposed 

skin, such as ears, to sense or track the fire conditions around them. While current protective 

equipment may have reduced the number of burns, especially to the ears, fire fighters still need 

to be able to assess fire conditions. 

Thermal sensing technology can provide fire fighters with the ability to monitor their 

thermal surroundings. However, in order to be effective, this technology must first be able to 

detect the thermal environment, and second must make the fire fighter aware of the thermal 

conditions in a manner that is timely and understandable. At this time, it is not clear whether 

tracking gas temperatures will provide better data than monitoring heat flux rates. While 

measuring temperatures or heat fluxes will provide important information, it may also be 

necessary to track the gradient or change in these quantities. In other words, the specific 

temperature may be important, but how quickly that temperature is achieved may provide 

additional insight into the developing fire environment. 

Thermal sensing technology including thermocouples or thermistors, and heat flux 

gauges can be incorporated into existing protective equipment or as stand-alone monitors. 

Multiple manufacturers of Personal Alert Safety System (PASS) devices offer models with 

thermal sensors incorporated into each device. If the temperature being monitored exceeds preset limits, the alarm signal is activated. At this time, thermal sensors have only been 

incorporated into non-integrated PASS devices and are not available on PASS devices that have 

been integrated into self-contained breathing apparatus (SCBA). Other fire safety equipment 

manufacturers offer stand-alone thermal sensing units which can be utilized to monitor 

temperatures in several different location inside or outside turnout gear. Early stand-alone 

systems such as Life Vest*∗ or Life Shirt, appeared to focus on temperature inside a fire fighter’s 

turnout coat. While these sensing units may provide warning of potential burn injuries or heat 

stress, these temperature monitors do not provide much data on changing conditions surrounding 

a fire fighter. 

∗ Certain trade names and company products are mentioned in the text or identified in an illustration in order to 

specify adequately the experimental procedure and equipment used. In no case does such identification imply 

recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the 

products are necessarily the best available for the purpose 

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Thermal sensors, such as the Fire-Eye (Figure 1) have been developed to track external 

gas temperatures and display this data directly to each fire fighter. Fire-Eye’s sensing unit and 

display mounts directly to the clear viewing section of the SCBA mask. As the temperature 

monitored near the face piece exceeds pre-determined values, a series of red and green light 

emitting diodes (LED) alert the fire fighter to changing conditions. The Fire-Eye device can be 

described as a ‘personal situation awareness tool’ that helps firefighters to make better decisions 

through providing an accurate indication of the temperature in the workspace surrounding them, 

and which ultimately seeks to reduce heat-related injuries and damage to equipment. 

While thermal sensing technology has already been included in different pieces of safety 

equipment, there are currently no standards or testing protocols with which to assess the 

performance of these thermal exposure sensors. While it is commendable that manufacturers 

seek to include more technology in order to increase the safety of fire fighters, the fire service 

does not have the resources to evaluate the thermal exposure sensor performance in stand-alone 

or integrated systems devices. There is a need for a well-designed testing protocol that would 

include different fire conditions that fire fighters typically encounter. This would allow the fire 

service to understand better the performance characteristics of the thermal sensors. In addition, 

a standardized testing protocol would allow the manufacturers to match the performance of their 

devices with the requirements of the fire service. 

Figure 1. Example of personal awareness tool, Fire-Eye display device along with the clip-box 

electronics unit. 

1.1 Heat Transfer Mechanism in the Fire Fighter Environment 

The experimental series included the different thermal conditions that fire fighters 

typically encounter. Within a fire scenario, there are three mechanisms by which thermal energy 

is transported: convection, conduction, and radiation. Convection is the transfer of heat by actual 

movement of the warmed matter or gases in the atmosphere; it is the transfer of heat energy in a 

gas or liquid by movement of currents. Conduction is the transfer of energy through matter from 

particle to particle; it is the transfer and distribution of heat energy from atom to atom within a 

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substance. Conduction is most effective in solids, but it can also happen in fluids. Radiation is 

the transfer of energy by electromagnetic waves that directly transports energy through space; it 

is the most efficient modes of transfer of heat energy across gas-filled volumes and it is the 

dominant mode in a typical fire.. A fire scenario may involve the transfer of heat energy with 

any combination of the three mechanisms. Therefore, it was necessary to evaluate the 

performance of a temperature-warning device in experimental conditions representing each of 

the three mechanisms. In order to validate the performance of the device in keeping with the 

elements above, the experimental matrix included examining the device in laboratory and fullscale experiments utilizing conductive, convective and radiative modes during the controlled 

exposure conditions. 

1.2 Situational Awareness Information Displays 

Timely display of fire ground data such as gas temperature, thermal flux values, and gas 

concentrations, is as important as collecting the data itself. This situational information must be 

displayed to the fire fighter quickly and in an understandable form. Firefighters and emergency 

responders are covered with protective gear while conducting firefighting or response activities; 

therefore, one possible method is to provide a visual warning which is directly in their line of 

sight. One method for providing this information to the fire fighter is through a visual display on 

or near the face piece. Manufacturers of personal protective equipment are beginning to 

introduce equipment with head mounted displays (HMDs) in which the information is conveyed 

to them through a Head-Up Display (HUD) or Head-Down Display (HDD). HUD is most 

prominently used in PPE for emergency responders. HUD has the potential to increase 

firefighter’s safety and make their work more efficient without interfering with their primary task 

of fighting a fire. Some of the typical devices in which HUDs are installed include display of 

thermal imaging data to locate a fire victim or fellow firefighter, or tactical information, such as 

maps or navigational information. The HUD warning system has also been used in the Fire-Eye 

device. The Fire-Eye device utilizes the location of the head visor to indicate various warning 

indicators, directly in the line of sight of the firefighter. There have been multiple applications of 

HMDs in fire department operations. HMDs are being effectively used by showing images 

recorded by a thermal imaging camera, and by displaying maps and the status of the equipment 

and the environment to the firefighters while they are inside the structure. The advantage of a 

HMD is that it is “hands-free.” HMDs can also be used in hazardous material operations, search 

and rescue after accidents, and also for detecting hot spots when the fire is extinguished. In the 

future, the amount of available electronic information from several sources (e.g., the firefighter 

himself, from sensors or external information from the command post) will highly increase the 

need for a “hands-free” device such as a HMD to display the relevant information (Bretschneider 

et al., 2006). 

1.3 Performance of Thermal Sensing Units Under Full-Scale Conditions 

This study examines the performance of a stand-alone thermal sensing unit in a series of 

full-scale experiments that were designed to document the response of externally mounted 

monitors. The performance of several thermal sensing devices were monitored through a series 

of live fires inside a ISO standard room using natural gas, heptane, and upholstered furnishings 

as fuel packages. Prior to the completion of the full-scale experiments, these same thermal 

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sensing devices were included in a series of laboratory-scale experiments which were described 

in a separate report (Deshmukh et al. 2013). 

1.4 Heat Release Rate and Fire Growth 

Heat Release Rate (HRR) is defined as the enthalpy change per unit of time as a result of 

the conversion of the chemical energy of a fuel to heat in a combustion process. Usually, the 

fuel is carbon-based and the combustion process is oxidation, which utilizes the available oxygen 

from the air. Heat release rate is usually reported in kilowatts (kW) or megawatts (MW) and is 

an important value because it is a key predictor of the hazard of fire, directly controlling the rate 

at which heat and the toxic gases build up in an enclosed structure or are driven into more remote 

spaces. The heat release rate is also the most pertinent measure of the size of a fire (Babrauskas, 

2002). 

Many different aspects of a fire can affect the performance of a heat-sensing warning 

device such as Fire-Eye. Any of the three kinds of heat transfer characteristics (i.e., conduction, 

convection, or radiation) can affect the status of the heat-sensing sensor of the device tested here, 

depending upon the intensity and type of fuel burning in the fire. Therefore, it is important to 

validate the performance of thermal sensing devices using different types of fuels, some 

generating soot, whereas others burning ‘cleanly’ (i.e., without soot). 

Fires typically grow from a small incipient fire to a large one through ignition and flame 

spread across the various fuels that are available in the environment. While attempting to 

evaluate the performance of a thermal sensing device in a realistic fire scenario, the overall size 

of the fire in the testing space and the fire’s spread over interior furnishings can significantly 

affect thermal sensing device performance. One method of evaluating the performance of the 

thermal sensor is to conduct realistic ‘room-corner’ tests in standard settings (e.g., living room, 

bedroom). Unlike laboratory-scale experiments, devices in the room-corner test are exposed to a 

full-scale fire scenario. In the conduct of such testing, thermal sensing devices should be 

mounted in an orientation that is representative of their potential use in real fire situations. The 

ignition source should ideally be kept consistent with a ‘naturalistic’ form of ignition (i.e., not 

artificial) in the room-corner tests. 

Several room-corner test protocols are currently in use by testing laboratories and are 

specified by entities such as ASTM, NFPA, the Uniform Building Code (UBC), and the 

International Standards Organization (ISO). The test arrangements and procedures for the 

specified room-corner tests are all similar, but there are some differences that can significantly 

affect the performance of the specimens being tested (Dillon, 1998). These differences include 

the size, location and energy release rate of the ignition burner as well the height and distance of 

the specimen from the fire. In order to produce the most representative, realistic fire scenarios, 

three different kinds of fuels are often used, including liquid sooty, gaseous clean, and wood and 

fabric (such as a couch, an end table, and a lamp). These fuels were used in the large-scale fire 

tests of the Fire-Eye device to be outlined below. The height and the distance of the facepieces 

that were mounted with the thermal sensing devices were representative of realistic fire 

conditions, such as the conduction-, convection-, and radiation-types of heat transfer that were 

described earlier. The primary measurements in the room-corner tests were temperature, the 

total heat flux at various locations, and the visual alarm signal performance of the thermal 

sensing devices. In order to avoid any structural damage to the ISO room and any other 

infrastructure used for the large-scale fire tests, the scenarios were designed to avoid flashover 

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temperatures (usually in the range of 800o C to 1000o C). Another valuable objective of the 

room-corner tests was to compare the performance of thermal sensing devices in the full scale 

fire tests with the previous laboratory-scale experiments. 

2.0 EXPERIMENTAL APPARATUS 

This section describes the various instruments, fuel characteristics, and the ISO room 

specifications. This section also describes the instrumentation used for measuring the 

temperatures, heat flux, and to collect the digital video recordings. 

2.1 ISO Room Specifications 

The facility used for testing the thermal sensing units was the ISO 9705 Full-scale room 

fire chamber (see Figure 2) at the Engineering Laboratory (EL) of the National Institute of 

Standards and Technology (NIST), Gaithersburg, MD. The ISO 9705-2003 room corner 

scenario is an internationally recognized standard test environment, and the tests conducted 

within it can be repeated and reproduced relatively easily. The ISO 9705 room dimensions are 

2.4 m wide x 3.6 m deep x 2.4 m high. The door (centered at the bottom of the front wall) in the 

front is 2.0 m high x 0.8 m wide. The exhaust hood for the ISO room (in front of the door 

receiving the gases exhausting from the front door) is 3.0 m wide x 3.0 m deep x 1.0 m high and 

the exhaust duct diameter is 0.4825 m. 

Figure 2. Schematic drawing of the ISO 9705 Room-Corner Test (Dillon, 1998). 

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2.2 ISO Room Construction 

A photograph of the ISO room is shown in Figure 3. The door in the front wall of the 

ISO room is the only access to the room. The room consists of a sheet metal stud framework 

lined with three layers of 1.27 cm thick gypsum wallboard and a single layer of 1.27 cm thick 

calcium-silicate board. The gypsum wall board can withstand temperatures in the range of 

800 oC to 1000 oC. The floor of the room is made up of cement board. 

Figure 3. ISO room and its exhaust hood. 

The gypsum board walls sometimes degrade when it is too hot inside the room; hence, 

cement flooring is used instead of gypsum board flooring. The large, instrumented exhaust hood 

allows for oxygen calorimetry and gas analysis to be performed on the exhaust gases originating 

from room fires. Oxygen consumption calorimetry consists of collecting all of the gases 

produced by the fire, measuring the rate of flow of the gases, sampling a small and well-mixed 

portion of the gases, and measuring the volume fractions of specific gas species, especially the 

oxygen volume fraction (Bryant et al., 2004). 

The ISO room was instrumented with two thermocouple arrays whose locations and 

specifications are described in the thermocouple array section (Section 2.4). Three water-cooled 

total heat flux gauges were used to record the heat flux at the target locations where the thermal 

sensing units were located. The burners for the first two types of fuels used in the experiments 

were located in the rear left corner of the room. The fuel was supplied through pipes that were 

connected to fuel storage tanks. The measurements for the physical locations of the fuel burners, 

thermal sensing units, thermocouple arrays, and the total heat flux gauges in the ISO room were 

measured from the rear leftmost corner of the room. Electric matches1 were used as an ignition 

1 Electric match consists of looping a section of bare high-resistant wire around the match heads in a book of 

matches. When a slight current is applied across the wire, the wire heats up and ignites the entire book of matches 

in a reproducible manner. 

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source for all experiments. The ignition spot for each large-scale experiment originated at the 

same place, located at the leftmost rear corner of the ISO room. 

2.3 Fuels Used for Large-Scale Fire Testing 

As stated earlier, three different types of fuels were selected to conduct the thermal 

sensing device performance validation in full-scale fire environment. The selection of fuel was 

based on the soot-production of the fuel as well as its resemblance to realistic fire scenarios in a 

structural fire. The first two fuels were fired using liquid fuel burners, whereas typical 

residential furnishings were used for the living room burn experiments. 

The first fuel selected for the first two experiments was natural gas. The natural gas heat 

of combustion was33.73 MJ/m3 (905.35 BTU/ft3

). The specific gravity of natural gas was 

assumed to be 0.6 and the flow coefficient was taken as 1.0. The heat of combustion per unit of 

oxygen (O2) is 12.55 MJ/kg of O2. Natural gas burns cleanly, essentially without yielding soot. 

Natural gas was supplied to the burner using a pipe connected to the cylinder inserted through 

the rear wall (see Figure 4) of the room. The size of the burner used for the experiment was 0.30 

m (1.0 ft) wide by 0.30 m (1.0 ft) long by 0.30 m (1.0 ft) high. The sand within the steel pan of 

the burner provided a resistance to the flow and resulted in the fuel being distributed more 

equally across the burner surface. The burner was spaced 15 cm (6 in) away from the left wall 

and 15 cm (6 in) away from the rear wall of the ISO room. The burner was ignited using a pilot 

light as shown in Figure 4. 

Figure 4. Natural gas burner. 

The second fuel selected for the full-scale fire experiments was heptane. The heat of 

combustion for n-heptane is 30593 kJ/L, its flow coefficient is 1.0, and the heat of combustion 

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per unit of oxygen (O2) is 12.68 MJ/kg of O2. Heptane produces large amount of soot while 

burning. The type of burner used for the heptane experiment was a ‘pan burner.’ The diameter 

of the pan burner was 0.61 m (24 in), and it was raised to a height of 0.46 m (18 in) from the 

floor of the ISO room using two vertically-oriented concrete blocks as shown in Figure 5. The 

pan was placed at a distance of 7.6 cm (3.0 in) from the left wall and 7.6 cm (3.0 in) from the 

rear wall of ISO room. 

Figure 5. Steel pan burner used for the heptane experiments. 

The burner was ignited via a pilot light as shown in Figure 5. The heptane was supplied from 

storage tanks through a pipeline that flowed through an opening in the bottom of the pan. 

The third fuel selected for the full-scale fire experiments was representative of the wood 

and synthetic fabric typically used in living room furniture. The fuel consisted of a couch, an 

end table, and a table lamp. Two identical sets of these items were procured from a local 

furniture store that sold used furniture. The couches were Niagara blue in color and were 

manufactured by Klaussner® Furniture Industries located in Asheboro, NC (see Figure 6). The 

length of the couch was 2.18 m (86 in), whereas the height of the couch from the ground 

including the two upright cushions was 0.73 m (29 in). The depth of the couch from its front 

corner to its rear corner was 0.91 m (36 in), and the height of the couch (excluding the cushion 

height) was 0.58 m (25 in). There were two upright backrest cushions and two horizontal 

cushions placed on the couch—the cushion in the upright position against the backrest was 0.91 

m (36 in) wide and 0.43 m (17 in) high. The weight of the couch without the upright cushion 

was 41.58 kg, and the two upright cushions weighed 5.53 kg (12.2 lb). The total weight of the 

couch including the cushions was 47.10 kg (103.6 lb). The cushions were filled with foam, and 

the external finish was made with a mixture of polyester-vinyl type of material. 

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Figure 6. Couch, end table, and lamp used in furnished room 

burns. 

The end table was 0.64 m (25 in) wide x 0.64 m (25 in) deep x 0.58 m (23 in) high, and 

weighed 13.7 kg (30.1 lb). The lamp and the shade were 0.43 m (17 in) high. The lamp was 

0.23 m (9 in) wide at the center and 0.15 m (6 in) wide at the base, and its shade was 0.46 m (18 

in) wide at the bottom, 0.18 m (7 in) wide at the top, and 0.28 m (11 in) high. The lamp and the 

shade together weighed 2.54 kg (5.6 lb) (Figure 6). 

2.4 Thermocouple Arrays 

Two vertical thermocouple arrays were positioned to monitor the thermal environment 

inside the ISO room (see Figure 6). Eight thermocouples were attached to each array at 0.30 m 

(1 ft) intervals from ceiling to floor. The highest thermocouple on each array was 2.5 cm 

(1.0 in) below the ceiling, whereas the second thermocouple on each array was exactly 0.30 m 

(1 ft) below the ceiling. All other thermocouples, from TC #3 through TC #8, were placed 0.30 

m (1 ft) apart, the last thermocouple being at the floor level. The thermocouples used in the 

array were Type K Chromel-Alumel thermocouples, which can withstand temperatures up to 

1260 o

C. The diameter of the sensing junction bead on each thermocouple was approximately 1 

mm. Typically, as the mass of the sensing junction bead increases, the time response of the 

thermocouple also increases. The time constant for these 1 mm diameter bare thermocouple 

beads was estimated at 2 seconds (Omega). 

During a typical room-corner experiment in the ISO 9705 room, a hot layer of gases 

develops at the top, and cold air moves into the bottom of the room. The thermocouples within 

the upper layer at the top 0.6 m to 0.9 m ( 2 ft- 3 ft) of the room display higher temperatures than 

the actual temperatures due to radiation cooling. The thermocouples at a distance of 0.3 m to 

0.6 m (1 ft-2ft) from the floor show a higher temperature than is the actual ambient temperature 

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due to radiative heating effects. Corrections for radiation heating or cooling were not applied to 

the temperatures recorded by the thermocouples in the room. 

2.5 Instrumentation of Thermal sensing units and Facepieces 

The nomenclature used for labeling the six thermal sensing units in Table 1 was also used 

in the full-scale fire experiments. Each Scott AV Face Mask 2000 model was equipped with a 

different thermal sensing unit. Each facepiece was instrumented with two thermocouples, one 

attached to the inside surface and the other attached to the outside surface of the transparent 

polycarbonate lens of the facepiece. Each thermal sensing unit except for unit #4 was 

instrumented with two thermocouples. Thermal sensing unit #4 was instrumented with three 

thermocouples. Ambient temperature thermocouples were also attached to each facepiece at a 

distance of 2.5 cm (1.0 in) from the thermal sensing unit, as in the laboratory-scale experiments. 

Each facepiece/thermal sensing unit had a minimum of five thermocouples attached, whereas the 

facepiece with thermal sensing unit #4 had six thermocouples attached. While testing the three 

thermal sensing units simultaneously, seven thermocouple channels were allocated to each mask 

in the Data Acquisition System (DAQ, discussed in detail below). Each thermocouple 

maintained a dedicated channel for data collection. The length of the thermocouples attached to 

the thermal sensing units averaged 6.1 m (20 ft). This length was not sufficient, however, to 

plug the other end of thermocouples in the DAQ. Therefore, thermocouple extension wires were 

used to plug the channels into the DAQ. 

Table 1: Nomenclature for the thermal sensing devices. 

Assigned Device 

Number 

Manufacturer’s Serial 

Number 

Thermocouple 

Specification 

1 10001629 TC1 and TC2 

2 10001708 TC1 and TC2 

3 10001638 TC1 and TC2 

4 10001623 TC1, TC2 and TC 5 

5 10001618 TC1 and TC2 

6 10001530 TC1 and TC2 

Table 2. Facepiece (FP) serial numbers and the thermocouples associated with them. 

Assigned Facepiece 

Number 

Manufacturers Serial 

Number 

Thermocouple 

Specification 

FP 1 804191-08 TC3 and TC4 

FP 2 804177-01 TC3 and TC4 

FP 3 802240-01 TC3 and TC4 

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2.6 Heat Flux Transducers 

Three calibrated Schmidt-Boelter total heat flux transducers were used to measure heat 

flux at three thermal sensing unit locations. The heat flux transducers are a water-cooled 

thermopile type, operating between 0 kW/m2 to 50 kW/m2. The transducers operate with a 

sensitivity of approximately 10 mV at 50 kW/m2. Each heat flux gauge measured 25 mm (1.0 

in) in diameter and had a metal flange located 25 mm (1.0 in) down its body and away from the 

sensing surface. Figure 7 shows a part of the heat flux gauge attached to the left side of the 

mask. Table 3 shows the serial numbers and dedicated data channels for the total heat flux 

gauges used at three mask locations. Each serial number had an independent calibration factor to 

convert the mV sensor output signal into a total heat flux in kW/m2, which was recorded by the 

DAQ. The three heat flux gauges were pointed towards the fire source so that they could record 

the heat flux at the location of each thermal sensing unit. 

Figure 7. Heat flux gauge mounted to the left of the facepiece. 

Table 3. Nomenclature for the heat flux gauges used at the three mask locations. 

Flux Gauge # Total Heat Flux 

Gauge Serial # 

Data Acquisition Channel 

Number Wattage 

Gauge 1 126844 Channel 3 20 W 

Gauge 2 126846 Channel 4 20 W 

Gauge 3 126842 Channel 5 20 W 

2.7 Data Acquisition System 

The DAQ also provided a user interface for control of the calibration burner’s output and 

to record the subsequent response of its instruments (Bryant et. al. 2004). The primary DAQ 

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board had 16 analog input channels at a 16-bit digital resolution and was capable of a sampling 

rate of 333 kHz. A total of 40 analog input signals were required for the calorimetry 

computation. Seven signal conditioning and multiplexing modules were employed and each 

module had a capacity for 32 input channels. The channels were scanned at a rate of 200 Hz and 

the signals were routed to a single channel on the primary DAQ board. Each multiplexed 

channel was electronically averaged for 1 s and the digital value was stored to the computer. The 

signal-conditioning features of the module included an electronic filter (200 Hz low-pass) and 

gain (amplifying up to 100 times). The gain was typically applied to low-voltage signals, such as 

those produced by the thermocouples (Bryant et. al. 2004). Figure 8 shows a picture of the 

thermocouples and heat flux gauges plugged into the data collection system. 

Figure 8. Data acquisition input unit for 

the thermocouples. 

The user interface for the DAQ was written in a LabView program that computed the 

heat release rate and displayed user-specified data and computations. The program was run on a 

workstation with dual 733 MHz processors and was located in the instrument control room of the 

NIST National Fire Research Laboratory. The output was displayed on the workstation monitor 

and was updated as the fire experiment proceeded. Figure 9 shows the two visual monitors 

utilized, each with three real time temperature channels and other experiment parameters 

displayed on the left of the screens. 

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Figure 9. Visual displays showing the fuel flow rate as well as temperatures at different 

locations. 

2.8 Digital Video Recording System 

The performance of three thermal sensing units was recorded simultaneously using three 

bullet cameras fitted into the head-forms as described in the laboratory-scale experiments 

(Deshmukh et.al 2013). For the Full-scale fire testing, the three bullet cameras were connected 

to three digital video recording units, each of which was powered by individual batteries. 

3.0 EXPERIMENTAL MATRIX 

Presented below is information outlining the experimental design used for the large-scale 

fire experiments, including devices, instrumentation, protocol, and setup. 

3.1 Qualitative Description of Mask Location 

Three masks were located at three different locations and elevations to simulate the 

realistic heat transfer circumstances of conduction, convection, and radiation. The heat flux 

density was typically highest at the mask closest to the fire, as it received the most radiation. 

The mask farthest from the heat source received the least amount of radiative heat, but was 

subjected to conductive heat. The mask at the higher elevation in the enclosed space received 

the most convective heat since the burning process pushed the heated gases high up into the 

structure. Since the room height was just 2.43 m (8.0 ft), the mask at an elevation of 1.52 m (5.0 

ft) from the floor received substantial heat from the heated gases. 

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 Door Door 

Symbols 

 

 

 

 

3.2 ISO Room Test Layout and Location of Masks 

The layout for the ISO room specific to each fuel experiment is displayed in Figure 10. 

A separate room layout was utilized for the natural gas and Heptane fuel experiments. Figure 11 

displays the location of Mask 1 in the ISO room, which was located diagonally at a distance of 

0.84 m (33 in) from the front corner of the natural gas burner, and 0.94 m (37 in) from the left 

wall. Mask 1 was elevated to a height of 0.3 m (1 ft) from the floor (in order to raise it to the 

level of burner) so that the heat generated from the burner was normally incident on the thermal 

sensing unit. The position of Mask 1 was maintained as the same for the heptane and the living 

room experiments for consistency. 

Experimental Layout 1 – Natural gas / Heptane Experimental Layout 2 – Living 

Room Burn 

B 

X (Ignition point) – Couch 

M 1 

M 2 

M 3 

M 1 

M 2 

B-X 

Mask 

B - Natural Gas and Heptane burner 

X – Ignition Point for a couch and end table burn experiment 

M1 – Mask 1 mounted with thermal sensing unit 5 

M2 – Mask 2 mounted with thermal sensing unit 3 or device 4 

M3 – Mask 3 mounted with thermal sensing unit 2 or device 6 

M 3 

T1 

T2 T2 

T1 

Thermocouple Tree 1 and 2 

Tree 1 (T1) – 0.9 m (3 ft) from the left wall and 0.9 m (3 ft) from the rear wall 

Tree 2 (T2) – 1.2 m (4 ft) from the left wall and 1.8 m (6 ft) from the rear wall 

Three heat flux gauges next to each mask 

Figure 10.	 Layout and arrangement of the facepiece and thermal sensing unit in the ISO room 

(Viewpoint is from the top down). 

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Figure 11. Mask 1 located at a height of 0.3 m (1 ft) from the ISO room floor. 

A diagonal distance of 0.84 m (33 in) was maintained from the radiant heat source in an 

effort to mirror the distance of the radiant panel as in the laboratory-scale experiments in a flux 

of 1.6 kW/m2. Heat flux gauge #1 was located on the same arc at a distance of 0.84 m (33 in) 

from the natural gas burner and to the left side of and close to Mask 1 (see Figure 11). The Mask 

1 location was representative of a firefighter operating very close to a fire source, and exposed to 

radiant heat generated from that source. 

Figure 12 displays the location of Mask 2 in the ISO room, which was at a distance of 6 

feet from the left wall and 1.8 m (6 ft) from the rear wall. Mask 2 was elevated 1.5 m (5 ft) 

from the room floor using an iron rod mounted on a stand. Mask 2 simulated the convective heat 

transfer condition of a fire. Heat flux gauge 2 was mounted on the same stand below Mask 2 as 

shown in Figure 12. During a real fire incident, the burnt gases and soot rise to the highest 

points in the enclosed structure (the space closest to the roof) while the oxygen is burning at the 

fire’s source. The elevation of Mask 2, therefore, was representative of a firefighter moving 

inside a burning fire toward the fire source or toward hot smoke, and the heated air moving in the 

direction of firefighter. 

Figure 12. Mask 2 located at a height of 1.5 m (5 ft) from the ISO room floor. 

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Figure 13 shows the location of Mask 3 in the ISO room. Mask 3 was located at a 

distance of 0.6 m (2 ft) from the left wall and 3 m (10 ft) from the rear wall, and was elevated to 

a height of 0.91 m (3.0 ft) from the room floor. Mask 3 simulated the conductive heat-transfer 

condition in a realistic fire scenario. Heat flux gauge #3 was mounted on the same stand, and 

below the Mask 3 as shown in Figure 13. During a real fire incident, the location of Mask 3 

would be representative of a fire fighter crawling or moving by bending his/her back in order to 

avoid the hot gas layer formed at a height of 1.5 m (5.0 ft) to 2.4 m (8.0 ft). At the height of 0.91 

m (3.0 ft) from floor, the conductive-type of heat transfer is more prominent than is radiation or 

convection. 

Figure 13. Mask 3 located at a height of 0.91 m (3 ft) from the ISO room floor. 

3.3 Experimental Design for the Full-scale Fire Experiments 

Figure 14 shows the experimental matrix for evaluating thermal sensing units in the fullscale fire facility. Experiment 1 and Experiment 2 were planned using natural gas fuel, whereas 

Experiment 3 and Experiment 4 were planned using liquid heptane fuel. Experiment 5 and 

Experiment 6 were conducted using living room furniture as a fuel. As per the experiment plan, 

two ISO room experiment burns were conducted using each type of fuel. In order to validate the 

performance of thermal sensing unit with different kinds of fuels, six experiments were 

performed over a period of two days. 

In order to examine the reproducibility of the thermal sensing unit, it was decided to use 

device number 5 (the same as for the laboratory-scale experiments). The full-scale fire 

experiments maintained a protocol of two repetitions for thermal sensing unit 5 with each fuel, 

whereas the laboratory-scale experiments had three repetitions for thermal sensing unit 5. In the 

six experiments, thermal sensing unit #5 was characterized at the same location (i.e., with Mask 

1) to help mitigate the variability that may have arisen due to a location change. 

In order to examine the repeatability of the thermal sensing unit, device numbers 2, 3, 4, 

and 6 were tested at different locations. In order to maintain consistency with the laboratoryscale experiments, these four devices were tested during two full-scale burns using the same fuel. 

Two devices were examined in the first burn and the remaining two devices were re-examined in 

the next burn using the same fuel. For example, TSU 2 and TSU 3 were at locations M3 and M2 

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(respectively) during the first burn, and TSU 4 and TSU 6 were at location M2 and M3 for the 

second burn. In order to reduce the set-up time (e.g., re-instrumentation) between the two 

experiments, and to mitigate any variability that may have presented with respect to a device 

location change, particular devices were maintained at the same position between fuel burns. 

Replacement of a device’s batteries and the fuel source were the only procedures undertaken 

between burns, which provided time for the thermal sensing units, bullet cameras, and the 

facepieces to cool before a subsequent experiment. 

FUEL 1 – NATURAL GAS FUEL 2 - HEPTANE 

EXPERIMENT 1 EXPERIMENT 3 

TSU 5 TSU 3 TSU 2 TSU 5 TSU 4 TSU 6 

M 1 M 2 M 3 M 1 M 2 M 3 

EXPERIMENT 2 EXPERIMENT 4
 

TSU 5 TSU 4 TSU 6 TSU 5 TSU 3 TSU 2 

M 1 M 2 M 3 M 1 M 2 M 3 

FUEL 3 – COUCH AND END TABLE
 

LIVING ROOM BURN 1 LIVING ROOM BURN 2 

EXPERIMENT 5 EXPERIMENT 6 

M 1 M 2 M 3 M 1 M 2 M 3 

TSU 5 TSU 3 TSU 2 TSU 5 TSU 4 TSU 6 

Figure 14. Experiment plan for the thermal sensing units in the full-scale fire facility. 

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4.0 EXPERIMENTAL PROCEDURES 

The experimental procedures followed for each of the full-scale fire experiments are 

presented below. 

4.1 Natural gas Experimental Procedure 

The relative humidity was 26% at the beginning of the natural gas experiment. The 

barometric pressure was 751 mm of mercury (Hg), and the ambient temperature of the space 

inside and outside the ISO room was 23o C. The criterion for terminating the natural gas 

experiments was to reach a temperature of at least 120o C at TC1 for Mask 1 and Mask 2, which 

would mirror the laboratory-scale experimental temperature conditions. The experimental 

procedure was as follows: 

1.	 Complete the instrumentation of the masks and the Thermal sensing units as per the 

experiment plan for natural gas experiment #1. 

2.	 Ready the three video recording units as well as adjust the bullet cameras to appropriately 

view the thermal sensing units. 

3.	 Program the DAQ to store the details of each experiment. 

4.	 Adjust the heat release rate (HRR) of the natural gas fuel to zero and record the time(s). 

5.	 Start the data acquisition computer and record a reference time. 

6.	 Ignite the gas burner inside the ISO room using the pilot light (see Figure 4). 

7.	 Record the ignition time and start the digital video recording system. 

8.	 Raise the HRR to 26.6 kW after 3 minutes from the time of ignition. 

9.	 Raise the HRR to 50 kW after 6 minutes from the time of ignition. 

10.	 Raise the HRR to 100 kW after 9 minutes from the time of ignition. 

11.	 Check the mask temperatures at M1TCI and M2TC1 and confirm whether they have
 

reached at a level of 120o C.
 

12.	 Reduce the HRR after 12 minutes to 0 kW and turn off the natural gas supply. 

13.	 Stop the HRR computer and data acquisition computer. 

14. Repeat the experiment for experiment plan #2 as per Figure 14. 

Figure 15. Full-scale fire experiment in progress using natural gas as fuel. 

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4.2 Heptane Experimental Procedure 

The relative humidity was 30% at the start of the heptane experiment. The barometric 

pressure was 751 mm of mercury (Hg), and the ambient temperature of the space inside and 

outside the ISO room was 16.1o C. The experiment terminating criteria for the Heptane 

experiments was to reach a temperature of 120o C at M1TC1 or M2TC1. The experimental 

procedure was as follows: 

1.	 Complete the instrumentation of the masks and the thermal sensing units for heptane 

experiment #1, per the experiment plan in Figure 14. Confirm that the data acquisition 

system is reading appropriate values for all 53 channels. 

2.	 Ready the three video recording units as well as adjust the bullet cameras to appropriately 

view the thermal sensing units. 

3.	 Program the DAQ to store the details of each experiment. 

4.	 Adjust the frequency of heptane flow to zero and record the time(s). 

5.	 Start the data acquisition computer and record a reference time. 

6.	 Ignite the heptane flow burner inside the ISO room using pilot light (see Figure 5). 

7.	 Record the ignition time and start the digital video recording system. 

8.	 After 3 minutes from ignition, raise the frequency of nozzle flow to 0.5 Hz to reach a 

HRR of 70 kW. 

9.	 After 6 minutes from ignition, raise the frequency of nozzle flow to 0.76 Hz to reach a 

HRR of 100 kW. Record the appropriate experiment status in lab notebook. 

10.	 After 9 minutes from ignition, raise the frequency of nozzle flow to 0.82 Hz to reach a 

HRR of 130 kW. Raise the frequency of nozzle flow to 0.76 Hz to reach a HRR of 100 

kW after 6 minutes from the time of ignition. 

11.	 Pull back Mask #1 in order to protect it from high radiative heat at the location of Mask 

1, and confirming that M1TC1 has reached a temperature of 120o

C. 

12.	 After 12 minutes from ignition, raise the frequency of nozzle flow to 1.0 Hz to reach a 

HRR of 160 kW. Stop the liquid fuel flow one minute after reaching a HRR of 160 kW. 

13.	 Check the temperature at M2TC1 and confirm whether it has reached at a level of 120o C. 

14.	 Turn off the heptane fuel supply. 

15.	 Stop the HRR computer and data acquisition computer. Repeat the experiment for 

second experiment plan as per Figure 14.
 

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Figure 16. Full-scale fire experiment in progress using heptane as a liquid fuel. 

4.3 Living Room Fire Experimental Procedure 

The relative humidity on the day of the living room fire experiment was 27 %. The 

barometric pressure was 749 mm/Hg, and the ambient temperature of the space inside and 

outside the ISO room was 21o C. The general experiment terminating criterion for the living 

room experiments was to avoid flashover temperatures more than 600o C to 800o C at the height 

of 7 to 8 feet from the floor. The specific experiment terminating criteria was to not allow the 

temperatures at M1TC1 and M2TC1 to rise above 160o C. Once the temperatures at either of 

these two TC reaches 160o C, then the fire would be extinguished with water sprinkler by a 

trained firefighter present at the time of testing. The experimental procedure was as follows: 

1.	 Arrange the couch, corner table, and table lamp as shown in the pre-experiment scenario 

in Figure 17. Maintain the location of the masks constant as in the earlier four 

experiments. 

2.	 Complete the instrumentation of the masks and the thermal sensing units for the living 

room experiment #1, per the experiment plan in Figure 14. Confirm that the DAQ is 

reading appropriate values in all 53 channels. 

3.	 Ready the three video recording units as well as adjust the bullet cameras to appropriately 

view the thermal sensing units. 

4.	 Program the data acquisition system to store the details of each experiment. 

5.	 Start the HRR computer and record the time (s). 

6.	 Start the data acquisition computer and record a reference time. 

7.	 Ignite the leftmost rear corner of the couch using the electric matches. A photograph of 

the living room experiment after ignition is shown in Figure 18. 

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Figure 17. Full-scale living room burn set-up before ignition. 

Figure 18. Living room fire experiment in progress after ignition. 

8.	 Track the temperatures inside the room as well as outside the mask and thermal sensing 

units from the data acquisition computer. 

9.	 Record the thermal sensing unit performance in the lab notebook. 

10.	 Suppress the fire by initiating water flow through sprinkler head above the furniture as 

soon as the criterion for termination of the experiment was reached in terms of 

temperatures in the upper layer of room. 

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11.	 Start the high-speed cooling fan to cool the ISO room and its contents. 

12.	 Record the damage done to the masks and the thermal sensing units by taking pictures of 

post-experiment scenarios. A post-fire scenario is shown in Figure 19. 

13.	 Stop the digital video recording units after recording 15 minutes of post-experiment 

cooling activities of thermal sensing units. 

Figure 19. After- the living room fire experiment. 

5.0 RESULTS 

The gas temperatures, thermal heat fluxes, and responses of the thermal sensing units for 

natural gas, heptane, and living room fire experimental scenarios are presented below. 

5.1 Temperature Profiles in the ISO Room 

The temperature profiles in the ISO room at the locations of Thermocouple Array 1 and 

Thermocouple Array 2 are displayed in Figures 20- 29. The graphs show the range of the 

temperatures reached in the upper, middle, and the lower level of the ISO room during each 

experiment. The figures ( 20 through 29) are arranged in the order that the experiments were 

conducted, and demonstrate that the intensity of temperatures increased from Experiment 1 

through Experiment 6. The natural gas experiment environment was the least intense 

temperature environment, whereas the living room fire experiment was the most intense 

temperature environment. The time span of a experiment was inversely proportional to the 

intensity of thermal environment of that experiment. Therefore, the natural gas experiments 

were the longest but less thermally intense experiments, whereas the living room fire 

experiments were the shorexperiment but most thermally intense experiments. The temperatures 

were recorded every second during the experiment, and each plot displays the temperature 

profile per second for the experiment duration. 

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T1TC1 T1TC4 T1TC7 

T1TC2 T1TC5 T1TC8 

T1TC3 T1TC6 

500 

400 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 20. Gas temperatures at Thermocouple Array 1 (T1) for Natural Gas Experiment #1.

T2TC1 T2TC4 T2TC7 

T2TC2 T2TC5 

T2TC3 T2TC6 

500 

400
 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 21. Temperatures at Thermocouple Array 2 (T2) for Natural Gas Experiment #1. 

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500 

T1TC1 

T1TC2 

T1TC3 

T1TC4 

T1TC5 

T1TC6 

T1TC7 

T1TC8 

400 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 22. Temperatures at Thermocouple Array 1 (T1) for Natural Gas Experiment #2. 

T2TC1 T2TC4 T2TC7 

T2TC2 T2TC5 

T2TC3 T2TC6 

500
 

400
 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 23. Temperatures at Thermocouple Array 2 (T2) for Natural Gas Experiment #2. 

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T1TC1 T1TC4 T1TC7 

T1TC2 T1TC5 T1TC8 

T1TC3 T1TC6 

500 

400 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 24. Temperatures at Thermocouple Array 1 (T1) for Heptane Experiment #1. 

T2TC1 T2TC4 T2TC7 

T2TC2 T2TC5 

T2TC3 T2TC6 

500 

400
 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 25. Temperatures at Thermocouple Array 2 (T2) for Heptane Experiment #1. 

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T1TC1 T1TC4 T1TC7 

T1TC2 T1TC5 T1TC8 

T1TC3 T1TC6 

500 

400 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Temperature, oC 

Figure 26. Temperatures at Thermocouple Array 1 (T1) for Heptane Experiment #2. 

T2TC1 T2TC4 T2TC7 

T2TC2 T2TC5 

T2TC3 T2TC6 

500 

400 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 27. Temperatures at Thermocouple Array 2 (T2) for Heptane Experiment #2. 

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T1TC1 T1TC4 T1TC7 

T1TC2 T1TC5 T1TC8 

T1TC3 T1TC6 

500 

400 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Temperature, oC 

Figure 28. Temperatures at Thermocouple Array 1 (T1) for Living Room Experiment #2. 

T2TC1 T2TC4 T2TC7 

T2TC2 T2TC5 

T2TC3 T2TC6 

500 

400 

Temperature, oC 

300 

200 

100 

0 

0 300 600 900 1200 

Time, s 

Figure 29. Temperatures at Thermocouple Array 2 (T2) for Living Room Experiment #2.

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5.2 Heat Flux Profile at Three Mask Locations

Voltage signal (V) outputs from each heat flux gauge were converted into heat flux 

values (kW/m2) using calibration graphs for each gauge. The heat flux values for the three 

masks in each experiment are displayed in the graphs that follow (Figures 30 -35).

Mask 1 Mask 2 Mask 3 

10 

8
 

Heat Flux, kW/m2 

6
 

4
 

2
 

0 

0 300 600 900 1200 

Time, s 

Figure 30. Heat Flux profile at three masks for Natural Gas Experiment #1. 

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Mask 1 Mask 2 Mask 3 

10
 

8

Heat Flux, kW/m2 

6 

4 

2 

0 

0 300 600 900 1200 

Time, s 

Figure 31. Heat Flux profile at three masks for Natural Gas Experiment #2. 

Mask 1 Mask 2 Mask 3 

10
 

8
 

Heat Flux, kW/m2 

6 

4 

2 

0 

-2 

0 300 600 900 1200 

Time, s 

Figure 32. Heat Flux profile at three masks for Heptane Experiment #1. 

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Mask 1 Mask 2 Mask 3 

10
 

8
 

Heat Flux, kW/m2 

6 

4 

2 

0 

-2 

0 300 600 900 1200 

Time, s 

Figure 33. Heat Flux profile at three masks for Heptane Experiment #2 

Mask 1 Mask 2 Mask 3 

10
 

8
 

Heat Flux, kW/m2 

6 

4 

2 

0 

-2 

0 150 300 450 600 750 900 

Time, s 

Figure 34. Heat Flux profile at three masks for Living Room Experiment #1. 

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Mask 1 Mask 2 Mask 3 

14 

10 

6 

2 

-2 

Time, s 

Figure 35. Heat Flux profile at three masks for Living Room Experiment #2. 

5.3 Results of the Natural Gas Experiments 

The Natural Gas Experiment flame height from the surface of the burner was between 

0.91 m (3 ft) and 1.2 m (4 ft) in both experiments (Figure 15). The ignition time was begun just 

after the experiment start time as the experiment was begun after initiating the bullet cameras as 

well as the data acquisition system and HRR computers. There was also a brief lag time between 

the fuel flow rate and actual HRR recorded at the burner. Table 4 shows separate rows for the 

begin time and ignition time for the Natural Gas Experiment #1. Table 5 shows the specific 

temperatures at TC1 and TC3 for specific thermal sensing units, when the warning indicators 

changed their blinking status during the experiment. 

Table 4. Timeline and details for Natural Gas Experiment #1. Heat Flux, kW/m2 

0 150 300 450 600 750 900
 

Natural Gas 

Experiment 1 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 0:10 0:10 0:10 

Blinking Green 8:34 10:25 18:30 

Solid Green 15:21 16:57 No change 

Solid Red 16:48 18:45 No change 

Blinking Red 17:33 19:42 No change 

Experiment end time 23:12 23:12 23:12 

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Table 5. Performance of the three thermal sensing units in Natural Gas Experiment # 1. 

Natural Gas 

Experiment 1 

Mask 1 (TSU#5) Mask 2 (TSU#3) Mask 3 (TSU#2) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green (oC) 62.4 65.2 66.3 59.3 54.0 59.3 

Solid Green (oC) 108.3 115.6 110.5 100.8 No change No change 

Solid Red (oC) 114.6 121.1 116.3 107.4 No change No change 

Blinking Red (oC) 115.6 122.4 120.0 110.6 No change No change 

The graph in Figure 36 shows the temperatures for the three thermocouples at the 

location of Mask 1. TC1 and TC3 are attached to the front surface of the TSU device and the 

facepiece, whereas TC5 is the ambient temperature sensing thermocouple. The graph in Figure 

37 shows the temperatures for the three thermocouples at the location of Mask 2, whereas the 

graph in Figure 38 shows the temperatures for the three thermocouples at the location of Mask 3. 

The graphs signify the difference in the temperatures at the surface of the TSU devices as well as 

the facepiece based on their location from the source of fire and their height from the floor. 

The timeline and the experiment details for Natural Gas Experiment #2 are shown in Tables 6 

and 7. Temperatures for Masks 1, 2, and 3 for Natural Gas Experiment #2 are graphed in 

Figures 39 – 41. 

M1T1 M1T3 M1T5 

Temperature, oC 

150 

120 

90 

60 

30 

0 

0 300 600 900 1200
 

Time, s 

Figure 36. Temperatures at Mask 1 for Natural Gas Experiment #1. 

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M2TC1 M2TC3 M2TC5 

150
 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 37. Temperatures at Mask 2 for Natural Gas Experiment #1.

M3TC1 M3TC3 M3TC5 

150
 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 38. Temperatures at Mask 3 for Natural Gas Experiment #1.

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Table 6. Timeline and details for Natural Gas Experiment #2. 

Natural Gas 

Experiment 2 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 0:10 0:10 0:10 

Blinking Green 6:24 7:18 12:04 

Solid Green 11:58 13:02 No change 

Solid Red 13:30 No change No change 

Blinking Red 14:30 No change No change 

Experiment end time 14:40 14:40 14:40 

Table 7. Performance of the three thermal sensing units in natural gas Experiment # 2. 

Natural Gas 

Experiment2 

Mask1 (TSU#5) Mask2 (TSU#4) Mask3 (TSU#6) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green(

o

C) 64.9 68.1 66.2 68.1 57.2 53.2 

Solid Green (oC) 105.8 114.1 111.2 103.4 No change No change 

Solid Red (oC) 101.4 117.2 No change No change No change No change 

Blinking Red (oC) 87.0 102.0 No change No change No change No change 

M1TC1 M1TC3 M1TC5 

0 

30 

60 

90 

120 

150 

0 300 600 900 1200 

Temperature, o C 

Time, s 

Figure 39. Temperatures at Mask 1 for Natural Gas Experiment #2. 

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150 

M2TC1 

M2TC3 

M2TC5 

M3TC6 

120 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 40. Temperatures at Mask 2 for Natural Gas Experiment #2.

M3TC1 M3TC3 M3TC5 

150
 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 41. Temperatures at Mask 3 for Natural Gas Experiment #2.

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5.4 Results of the Heptane Experiments 

The heptane experiment flame height from the surface of the burner was between 0.91 m (3 ft) 

and 1.2 m (4 ft) for both experiments (see Figure 16). The ignition time was begun just after the 

experiment begin time as there was a time lag between the fuel flow rate and the actual HRR 

recorded at the burner. The timeline and the experiment details for Heptane Experiment #1 are 

shown in Table 8. The temperatures at the thermal sensing units attached to each mask for 

Heptane Experiment #1 are graphed in Figures 42 - 44. Table 9 shows the specific temperatures 

at TC1 and TC3 for specific thermal sensing units, when the warning indicators changed their 

blinking status during the experiment. The timeline and the experiment details for Heptane 

Experiment #2 are shown in Tables 10 and 11. Temperatures for Masks 1, 2, and 3 for Heptane 

Experiment #2 are graphed in Figures 45 – 47. 

Table 8. Timeline and details for Heptane Experiment #1. 

Heptane Experiment 

1 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 1:25 1:25 1:25 

Blinking Green 2:35 2:30 8:35 

Solid Green 12:09 9:55 No change 

Solid Red 13:20 12:12 No change 

Blinking Red 14:37 13:15 No change 

Experiment end time 17:05 17:05 17:05 

Table 9. Performance of the three thermal sensing units in Heptane Experiment # 1. 

Heptane 

Experiment 1 

Mask 1 (TSU#5) Mask 2 (TSU#4) Mask 3 (TSU#6) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green(

o

C) 61.4 70.0 73.2 67.1 30.9 53.3 

Solid Green (oC) 117 119.8 124.7 107.6 No change No change 

Solid Red (oC) 112.5 121.8 43.0 123.9 No change No change 

Blinking Red (oC) 104.5 109.5 149.6 130.0 No change No change 

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M1TC1 M1TC3 M1TC5 

150
 

120
 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 42. Temperatures at Mask 1 for Heptane Experiment #1.

M2TC1 M2TC6 

M2TC3 M2TC5 

180 

150 

120 

90 

60 

30 

Temperature, oC Temperature, oC 

90
 

0 

0 300 600 900 1200 

Time, s 

Figure 43. Temperatures at Mask 2 for Heptane Experiment #1.

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M3TC1 M3TC3 M3TC5 

Temperature, oC 

150 

120 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 44. Temperatures at Mask 3 for Heptane Experiment #1. 

Table 10. Timeline and details for Heptane Experiment #2. 

Heptane Experiment 

2 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 0.00 0.00 0.00 

Blinking Green 3:40 No response 7:15 

Solid Green 10:20 No response No change 

Solid Red 11:10 No response No change 

Blinking Red No change No response No change 

Experiment end time 12:00 12:00 No change 

Table 11. Performance of the three thermal sensing units in Heptane Experiment # 2 

Heptane 

Experiment 2 

Mask1 (TSU#5) Mask2 (TSU#3) Mask3 (TSU#2) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green (oC) 60.1 62.7 No response No response 27.4 48.9 

Solid Green (oC) 106.2 111.0 No response No response No change No change 

Solid Red (oC) 111.9 117.3 No response No response No change No change 

Blinking Red (oC) No 

change 

No 

change No response No response No change No change 

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M1TC1 M1TC3 M1TC5 

150
 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 45. Temperatures at Mask 1 for Heptane Experiment #2.

M2TC1 M2TC3 M2TC5 

150
 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 46. Temperatures at Mask 2 for Heptane Experiment #2.

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M3TC1 M3TC3 M3TC5 

Temperature, oC 

150 

120 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 47. Temperatures at Mask 3 for Heptane Experiment #2. 

5.5 Results of the Living Room Fire Experiments 

The living room fire experiments were the shortest experiment experiments conducted in the ISO 

room, with durations of 180 s and 140 s. As explained earlier, these experiments were short in 

an effort to avoid the flashover temperatures that could have damaged the infrastructure of the 

ISO room as well as the masks and thermal sensing units. Even though care was taken to avoid 

flashover temperatures, the temperatures in the upper layer of the room were measured to reach 

above 600o C. The flame height from the couch was measured to be in the range of 1.2 m (4 ft) 

to 1.5 m (5 ft) from the floor. The timeline and the experiment details for Living Room 

Experiment #1 are shown in Table 12. Table 13 shows the specific temperatures at TC1 and 

TC3 for specific thermal sensing units, when the warning indicators changed their blinking status 

during the experiment. The temperatures at the thermal sensing units attached to each mask for 

Living Room Experiment #1 are graphed in Figures 48 - 50. The timeline and the experiment 

details for Living Room Experiment #2 are shown in Tables 14 and 15. Temperatures for Masks 

1, 2, and 3 for Heptane Experiment #2 are graphed in Figures 51 – 53. 

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M1TC1 M1TC3 M1TC5 

Time, s 

Table 12. Timeline and details of Living Room Experiment #1. 

0 

30 

60 

90 

120 

150 

0 300 600 900 1200 

Temperature, o C 

Living Room 

Experiment 1 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 0:40 0:40 0:40 

Blinking Green 2:33 2:23 3:20 

Solid Green Skipped Skipped No change 

Solid Red 2:45 2:25 No change 

Blinking Red No change No change No change 

Experiment end time 3:00 3:00 3:00 

Table 13. Performance of the three thermal sensing units in Living Room Experiment # 1. 

Living Room 

Experiment 1 

Mask 1 (TSU#5) Mask 2 (TSU #4) Mask 3 (TSU#2) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green (oC) 63.2 77.7 102.7 92.1 43.1 49.5 

Solid Green (oC) No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

Solid Red (oC) 59.3 75.4 95.0 92.6 No 

change 

No 

change 

Blinking Red (oC) No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

41 Figure 48. Temperatures at Mask 1 for Living Room Experiment #1. 

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M2TC1 M2TC6 

M2TC3 M2TC5 

30 

80 

130 

180 

230 

0 300 600 900 1200 

Temperature, o C 

Time, s 

Figure 49. Temperatures at Mask 2 for Living Room Experiment #1. 

M3TC1 M3TC3 M3TC5 

150
 

120
 

Temperature, oC 

90
 

60
 

30
 

0
 

0 300 600 900 1200
 

Time, s
 

Figure 50. Temperatures at Mask 3 for Living Room Experiment #1.
 

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Table 14. Timeline and details for Living Room Experiment #2. 

Living Room 

Experiment 2 

Mask 1 Mask 2 Mask 3 

Experiment begin time 0:00 0:00 0:00 

Time at ignition 1:00 1:00 1:00 

Blinking Green 3:00 2:58 3:12 

Solid Green Skipped Skipped Skipped 

Solid Red 3:11 3:09 3:25 

Blinking Red No change No change No change 

Experiment end time 3:35 3:45 3:45 

Table 15. Performance of the three thermal sensing units in Living Room Experiment #2. 

Living Room 

Experiment 2 

Mask 1 (TSU#5) Mask 2 (TSU#4) Mask 3 (TSU#6) 

Temperature (oC) M1TC1 M1TC3 M2TC1 M2TC3 M3TC1 M2TC3 

Blinking Green (oC) 51.9 89.2 115.6 138.5 40.6 53.9 

Solid Green (oC) No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

Solid Red (oC) 55.5 80.9 106.8 136.5 43.3 55.7 

Blinking Red (oC) No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

No 

change 

M1TC1 M1TC3 M1TC5 

Temperature, oC 

150 

120 

90 

60 

30 

0 

0 300 600 900 1200 

Time, s 

Figure 51. Temperatures at Mask 1 for Living Room Experiment #2. 

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M2TC1 M2TC5 

M2TC3 M2TC6 

420
 

360 

300 

240 

180 

120 

60 

Temperature, oC 

0 

0 300 600 900 1200 

Time, s 

Figure 52. Temperatures at Mask 2 for Living Room Experiment #2. 

M3TC1 M3TC3 M3TC5 

420
 

360
 

0 300 600 900 1200
 

Temperature, o

C

300 

240 

180 

120 

60 

0 

Time, s 

Figure 53. Temperatures at Mask 3 for Living Room Experiment #2. 

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5.6 Experimental Uncertainty 

There are different components of uncertainty in the positioning, temperature, thermal 

flux, and time data reported here. Uncertainties are grouped into two categories according to the 

method used to estimate them. Type A uncertainties are those which are evaluated by statistical 

methods, and Type B are those which are evaluated by other means [Taylor 1994]. Type B 

analysis of systematic uncertainties involves estimating the upper (+ a) and lower (- a) limits for 

the quantity in question such that the probability that the value would be in the interval (± a) is 

essentially 100 %. After estimating uncertainties by either Type A or B analysis, the 

uncertainties are combined in quadrature to yield the combined standard uncertainty. 

Multiplying the combined standard uncertainty by a coverage factor of two results in the 

expanded uncertainty which corresponds to a 95 % confidence interval (2σ). 

Components of uncertainty are tabulated in Table 16. Some of these components, such as 

the zero and calibration elements, are derived from instrument specifications. Other 

components, such as radiative cooling/heating include past experience with thermocouples in 

high temperature environments. 

The uncertainty in the gas temperature measurements includes radiative cooling in each 

of the experiments series, but also includes radiative heating for thermocouple located inside the 

facepiece. Gas temperature measurements were monitored up 140 o

C. There were no 

temperature fluctuations of large magnitude and typically the temperature changed slowly. 

Thermocouples were located in hot and cool locations. When positioned in hot gases, the 

thermocouple beads would have radiated some energy to the cooler objects such as the facepiece 

or headform and this radiative cooling could have caused the recorded temperature to be lower 

than the actual gas temperature. On the other hand, a thermocouple positioned inside the 

facepiece would have been in a cooler environment, but radiation from the hotter gases could 

have radiated some energy to the thermocouple bead causing radiative heating of the bead. 

This could have caused the recorded temperature to be greater than the temperature inside the 

facepiece. Calibration data was obtained from the thermocouple manufacturer and the 

measurements were very repeatable. This resulted in an estimate of -32 % to +15 % total 

expanded relative uncertainty for the temperature measurements. 

Calibration of heat flux gauges was completed at lower fluxes and then extrapolated to 

higher values and this resulted in a higher uncertainty in the flux measurement. Combining all 

of component uncertainties for total heat flux resulted in a total expanded uncertainty of – 23% 

to + 23 % for the flux measurements. Estimating the uncertainty in the thermal sensing unit 

response or activation temperature for the static oven and flow loop experiments required the 

uncertainties in air temperature, alarm activation, and repeatability to generate a total expanded 

uncertainty range of –27 % to +29 %. In all the experimental experiment series, uncertainty in 

the physical position of the instrumentation such as thermocouples or heat flux gauges was 

estimated to have the lowest total expanded uncertainty of ± 11 %. 

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Table 16: Uncertainty in full-scale experimental data. 

Component 

Standard 

Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

GasTemperature 

Calibration ± 1 % 

Radiative Cooling - 15 % to + 0 % - 16 % to + 8 % - 32 % to + 15 % 

Radiative Heating - 0 % to + 5 % 

Repeatability 1 ± 5 % 

Random 1 ± 3 % 

Total Heat Flux 

Calibration ± 10 % 

Zero - 2 % to + 2 % 

Repeatability 1 

Random 1 

± 5 % 

± 3 % 

- 12 % to + 12 % - 23 % to + 23 % 

Activation 

Temperature 

Zero 

Temperature 

Alarm/Light 

Activation 

Repeatability 1 

Random 1 

± 2 % 

± 12% 

-0 % to + 5 % 

± 5 % 

± 3 % 

- 13% to + 14% - 27 % to + 29 % 

Instrument Location 

Zero ± 1 % 

Repeatability 1 ± 5 % ± 5 % ± 11 % 

Random 1 ± 2 % 

Notes: 1. Random and repeatability evaluated as Type A, other components as Type B. 

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6.0 DISCUSSION 

The response of the thermal sensing units across the three experiments was different, 

depending upon the intensity and the rate of increase of heat in a particular experiment. None of 

the thermal sensing units deformed or melted in any of the Full-scale fire experiments. 

However, some surface marks and scratches were noticed on thermal sensing units #5 and #4 at 

the conclusion of the living room fire experiments. This was likely due to the fact that the 

temperatures for those experiments increased drastically within several seconds, perhaps 

demonstrating one of the most hazardous conditions for firefighters and their protective gear. 

Thermal sensing unit #5 (located at Mask 1, see Figure 14 for location) survived the complete 

experiment regimen. Thermal sensing units #2, #4, #5, and #6 were noted to indicate ‘sudden 

hot conditions through actuation of their solid red indicator immediately after the green blink 

indicator, when the temperatures increased to more than 200o C within a few seconds during the 

living room fire experiments. 

As stated earlier, Mask 1 represented the position of thermal sensing unit when exposed 

to intense radiation. Thermal sensing unit #5 was tested for reproducible performance at Mask 1 

in all three of the experiments. That device consistently indicated ‘blinking green’ for both of 

the natural gas experiments between the temperatures of 60o C to 65o C. Thermal sensing unit #5 

also produced a ‘blinking green’ indicator between the temperatures of 68o C to 73o C for both of 

the heptane experiments, whereas the same device produced a ‘blinking green’ indicator between 

the temperatures 68o C to 73o C momentarily in the living room fire experiment. 

The thermal sensing unit #5 at Mask 1 responded first in both of the natural gas 

experiments, followed by the devices at Mask 2 and Mask 3. The thermal sensing units #3 and 

#4 at Mask 2 responded first in the first heptane experiment and the two living room fire 

experiments, followed by the thermal sensing unit #5 at Mask 1 and thermal sensing unit #2 and 

#6 at Mask 3. The response of Mask 1 in the natural gas experiment is consistent with the 

intense radiant heat that was incident upon the mask was due to the height of the burner and the 

mask being the same, exposing it to increased radiative heat when compared to Mask 2 and 

Mask 3. 

The thermal sensing unit at Mask 2 responded earlier than the thermal sensing unit at 

Mask 1 in the Heptane Experiment # 1 due to a hot upper layer of gases formed in the ISO room 

after ignition. The heptane burns produced large amounts of soot that led to the formation of a 

heated gas layer in the upper volume of the room. The hot soot layer was seen up to 1.2 m (4 ft) 

from the ceiling of the room. In this hot soot layer, Mask 2 was at a height of 1.5 m (5 ft) above 

the floor, just at the height of the soot layer. These hot layers of gases resulted in a convective 

heat transfer to Mask 2, which led to it being heated and its attached thermal sensing unit 

indicators actuating earlier than for Mask 1 or Mask 3. Mask 1 was located at a distance of a 0.3 

m (1ft) above the floor, so it was lower in elevation than the heptane burner height by 0.15 m (6 

in). This would have been consistent as to why Mask 1 did not experience radiation as intense as 

in the natural gas experiments. The thermal sensing unit at Mask 3 responded later in the 

heptane experiments as well. 

The thermal sensing unit at Mask 2 responded earlier than the device at Mask 1 in the 

living room fire experiments as well, but the difference in the response time of the two devices 

was between 5 s to 10 s. The couch was ignited at the rear leftmost point in the room, leading to 

large amounts of soot production from the left corner to the nearest ‘cooler region,’ which was 

located in the upper volume of the ISO room. The hot layer of sooty gases in the living room 

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fire experiments was noted to be at a height of 1.2 m (4 ft) from the floor of the room, resulting 

in the condition that half of the room was filled with hot gases. This hot layer resulted in 

increased convective heat transfer to Mask 2, leading to display of the ‘blinking green’ indicator. 

Interestingly, Mask 1 and Mask 2 did not display the ‘solid green’ indicators and instead went 

straight to the ‘solid red’ indicators within 10 s, suggesting the development of hazardous 

conditions within 120 s after the experiment ignition. 

The thermal sensing unit at Mask 3 also responded quickly in the two living room fire 

experiments when compared to the natural gas or heptane experiments, likely due to the intense 

heat and smoke that was generated within a 120 s time period, and was noted to actuate the ‘solid 

red’ indicator within 10 s of actuating the ‘blinking green’ indicator, providing a ‘validation’ of 

sorts regarding the hazardous scenario that was existing in the ISO room at that time. Further, 

the thermal sensing unit at Mask 3 was noted to actuate only the ‘blinking green’ indicator in the 

natural gas and heptane experiments due to the (comparatively) limited conductive heat transfer 

characteristic of those experiments. As such, the ‘slowest’ indicator response was from the 

thermal sensing unit at Mask 3 in 4 of the 6 experiments conducted in the ISO room, whereas the 

devices at Mask 1 and Mask 2 responded quickly depending upon the intensity, the rate of 

increase of temperature, and the hot upper layer of gases created in the ISO room. Figure 54 

shows the post-experiment condition after Living Room fire Experiment #2. Thermal sensing 

unit #3 failed to indicate any warning indicators in Heptane experiment #2 at the location of 

Mask 2. The cause of this apparent malfunction was unknown. The recorded gas temperatures 

in Heptane experiment #1 were higher than in Heptane experiment #2. The impact of repeated 

or cyclical exposures of a sensing unit to thermal conditions was not examined during this 

limited set of full-scale experiments. 

Figure 54. Post-experiment condition of the ISO experiment room for the living room fire 

experiment. 

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Figure 55 displays the post-experiment condition of the three masks exposed to the fire 

during living room fire experiment #2, one of the most intense experiments conducted in the ISO 

room. Mask 2 on the left of the image was the most damaged; it was located 1.5 m (5 ft) from 

the floor, and its damage was due to convective heat transfer in the upper layer. The damage 

included deformation of the polycarbonate lens and thermal decomposition of the plastic heads 

of the mounting screws for the lens. No crazing (formation of fine lines or surface cracking) or 

bubbling of the lens was observed. Soot was also deposited onto exposed surfaces of the mask 

and lens. Mask 3 on the right side of Figure 55 was the least damaged mask, and its placement 

further away from the fire and in the lower layer primarily represented the conditions of 

conductive heat transfer. Mask 1 in the middle exhibited less damage than Mask 2 that was 

exposed in the upper layer. Some deformation, but no crazing or bubbling, of the lens was 

observed. 

Figure 55. The post-experiment condition of the three masks after Living Room Experiment #2. 

Figure 56 shows thermal sensing unit #4 mounted on Mask 2 at a height of 1.5 m (5 ft) 

from the floor (this was the most damaged mask after the living room fire experiment). Figure 

57 displays thermal sensing unit #5, which was at a height of 0.3 m (1 ft) above the floor, and 

closest to the source of the fire (this device was exposed to the most heat from the source that 

due to radiation heat-transfer). Thermal sensing unit #5 was deformed, but was not as heavily 

damaged as unit # 4 that was positioned at a height of 1.5 m (5 ft) above the floor. 

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Figure 56. Mask #2 resulting from convective heat-transfer, and which was 

positioned at a distance of 1.5 m (5 ft) above the floor. 

Figure 57. Mask #1, located at a height of 0.3 m (1 ft) above the 

floor, and closest to the source of the fire. 

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9.0 COMPARISON OF THERMAL SENSING UNITS IN FIRE USING DIFFERENT 

FUELS 

The thermal sensing units performed consistently for all three types of fuels used in the 

full-scale fire experiments. The performance of the devices was based on the heat generated in 

each type of experiment rather than the type of fuel because of the nature of the heat sensors (i.e., 

they detect heat, no matter what is the source). Figures 20 through 29 show the temperature 

profile in the ISO room at the two thermocouple arrays. The data indicate that the temperatures 

at higher elevations in the room reached a level of 400o C to 450 o C during the living room 

experiments, whereas these temperatures were lowest in the natural gas experiments (i.e., 200 o C 

to 250 o C), and the heptane experiments were in between these two ranges. The heat flux that 

was generated in the six experiments was in the range of 1 kW/m2 to 14 kW/m2

, as shown in 

Figures 30 through 35. A heat flux of 6.4 kW/m2 causes the human skin to experience pain with a 

1 s exposure and blisters the skin in 18 s with second-degree burn injury (NFPA, 1971). A heat 

flux of 10.4 kW/m2 , however, causes the human skin to experience pain with a 3 second 

exposure and blisters the skin in 9 seconds with a second-degree burn injury. A heat flux of 12.5 

kW/m2 causes wood volatiles to ignite with extended exposure and piloted ignition (NFPA, 

1971). The earlier specified values of heat flux renders comparison of the heat flux values 

attained in the full-scale fire experiments relatively easy. 

In the two full-scale living room experiments, the couch and the side table did not burn in 

the same manner. In the first living room experiment, the experiment-terminating criteria was 

exercised stringently, whereas the second living room experiment was allowed to continue 

further in order to assess the performance of the devices in extremely hot conditions, when the 

risk of the mask and the thermal sensing unit being destroyed was greater. 

10.0 CONCLUSIONS 

A limited series of thermal exposure experiments in a full-scale room provide 

performance data for thermal sensing technology. Full-scale exposures such as those described 

in this report provide insight as to how energy or heat transferred via conduction, convection, 

and radiation can impact the performance of thermal sensing units. During these thermal 

exposures, masks with thermal sensing units were positioned in locations that were designed to 

expose the devices to high thermal radiative flux (Mask 1), high convective heat flux (Mask 2), 

and low thermal radiative and convective flux (Mask 3). Fuels were varied from natural gas, to 

liquid heptane, to typical furniture. During each experiment and at each location, the thermal 

sensing units typically survived the thermal conditions, tracked the gas temperatures, and 

provided a visual display linked to the thermal conditions. The display of solid or blinking 

green and red LEDs would provide the fire fighter with real time update as to the changing 

thermal conditions. 

During thermal exposures, gas temperatures and heat fluxes were monitored as well as 

sensing unit temperatures to characterize how the thermal sensing unit responded to changing 

thermal conditions. As one would expect, the gas temperatures demonstrate significant 

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differences in thermal conditions at each mask location. The mask nearest the fire experienced 

the highest radiative thermal flux while the mask most distant from the fire experienced 

significantly less radiative and conductive fluxes. The heat flux that was generated in the six 

experiments was in the range of 1 kW/m2 to 14 kW/m2

. 

Thermal sensing units melted or deformed in the full-scale experiments, wherein the heat 

flux reached a maximum level of 14 kW/m2 for a few seconds. A thermal sensing unit did fail 

during a heptane fire experiment. It was not clear why the sensing unit failed. The devices also 

did successfully function in the different kinds of environments generated by burning three 

different types of fuels. The results from the full-scale testing suggest that the thermal sensing 

unit can withstand flame-resistant experiments and can perform in highly convective and 

radiative heat environments, but the temperatures at which the warning indicators are triggered 

also vary considerably according to the characteristics of the environment in which they are 

tested. Similarly, there are some inconsistencies in the warning indicators subject to the 

exposure in similar environments. It was observed that the repeatability and reproducibility of 

the thermal sensing unit were less consistent from experiment to experiment in the full-scale 

testing as compared to the laboratory-scale experiments (Deshmukh et al. 2013), likely due to the 

difference between the controlled and uncontrolled environments. 

Combining the results of these full-scale experiments with the previous lab-scale 

experiments suggests that thermal sensing technology could provide the fire fighter with 

information about the thermal conditions whether the fire fighter was standing still, moving 

through smoke, or exposed to flaming conditions. The differences observed in the gas 

temperatures also demonstrate the need to examine the performance of all situation awareness 

technology in each of the scenarios. The impact of repeated thermal exposures on the sensing 

unit also needs to be characterized better. Standard testing protocols need to include 

conduction-, convection-, and radiation-dominated thermal conditions because fire fighters are 

exposed to all three scenarios. 

Thermal sensing units can provide a fire fighter or emergency responder with information 

about their environment, but currently technology can only provide a snapshot of current 

conditions. The technology may include some past exposure as it displays information, but the 

technology can’t predict future conditions. In this work, a thermal sensing unit can detect the 

change from previous thermal conditions, but it can not predict whether a fire is decreasing or 

increasing in heat release rate. This implementation of thermal sensing technology displays a 

change in conditions, but does not provide information about how long the fire fighter has been 

exposed to these conditions or whether the fire fighter should evacuate. Even if this technology 

provided the fire fighter with a signal to evacuate, would a series of green and red LEDs be 

sufficient to cause a fire fighter to retreat? Obviously, thermal sensing units can only help the 

fire fighter be aware of their environment and their response or action to that information rests on 

their training and their ability to use the information. 

Situational awareness technology can provide the fire service with more information that 

can be utilized by the fire fighter to understand the thermal conditions in which they are 

operating. With training, the fire fighter will be better able to use this data or understanding to 

work more safely and more effectively. It will be important that all situational awareness 

technology be able to survive and function in multiple exposures to the wide range of conditions 

that fire fighters experience. Representative performance metrics and standard testing protocols 

would allow the fire service to better understand the performance characteristics of the thermal 

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sensors. In addition, a standardized testing protocol would allow the manufacturers to match the 

performance of their devices with the requirements of the fire service. 

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