NIST Technical Note 1803 

Thermal Exposure Sensor for Fire 

Fighters- Laboratory-Scale 

Performance Experiments 

Atul Deshmukh 

John G. Casali 

Jeff A. Lancaster 

Nelson P. Bryner 

Roy A. McLane 

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NIST Technical Note 1803 

Thermal Exposure Sensor for Fire 

Fighters- Laboratory-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 

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http://dx.doi.org/10.6028/NIST.TN.1803 

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 1803 

Natl. Inst. Stand. Technol. Tech. Note 1803, 46 pages (July 2016) 

CODEN: NTNOEF 

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Thermal Exposure Sensor for Fire Fighters – LaboratoryScale Performance Experiments 

ABSTRACT 

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

insulate them from high temperature environments, including hot combustion gases, 

burning surfaces, and thermal radiation. Current turnout gear insulates the fire fighter to 

such an extent, encapsulating his/her entire body, that it is difficult for each individual 

fire fighter to understand how hazardous or hot the thermal environment is. Therefore, 

the natural heat-sensing 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. This 

report describes the laboratory-scale experiments and a second report describes the fullscale fire experiments. A static oven, representing the conductive type of heat; a fire 

equipment evaluator, with high speed convective flow loop, and a radiant panel, with 

intense heat flux were used to conduct laboratory-scale experiments. 

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LIST OF ACRONYMS
 

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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 Laboratory 

BTU/ft3 BTU per cubic feet 

cm Centimeter 

Cr Chromel o

C Degrees Centigrade 

DAQ Data Acquisition System 

DV Digital Video 

E# 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 

% Percentage 

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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 both 

be able to detect the thermal environment, and 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. 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 pre-set 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 

∗ 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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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. 

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, a Fire-Eye device along with the clip-box 

electronics unit. 

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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 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 full-scale 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 

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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 Laboratory-Scale Conditions 

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

series of laboratory scale experiments that were designed to document the response of an 

externally mounted monitor that was located at the top of the facepiece lens. The 

performance of several thermal sensing devices of the same design were monitored 

through a series of carefully controlled heated oven and radiant panel exposures. After 

completion of the laboratory experiments, these same thermal sensing devices will be 

included in a series of full-scale experiments. The full-scale experiments are described 

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

2.0 EXPERIMENTAL APPARATUS 

The experimental set-up for the laboratory-scale experiments included 

instrumented headforms and thermal sensing units, respirator facepieces, and a data 

acquisition system. The headforms and thermal sensing units were exposed to thermal 

conditions in a static oven, flow loop, and radiant panel apparatus. 

2.1 Instrumented Headform 

The headforms used in the laboratory experiments were made from white closedcell foam. Each headform had a flat base that allowed it to be mounted securely on a flat 

surface. Due to the severe temperatures to which they were exposed (up to 200 o

C), a 

large portion of the headform surface was covered with fiberglass heat-resistant tape as 

shown in the left side of Figure 2. As per the manufacturer’s product specifications, the 

heat-resistant tape can withstand temperatures in the range of 204 oC to 530 oC (400 oF to 

1000 oF). In order to insert a bullet video camera along with its power cord, the 

headform was drilled at an angle of 40 ° facing up from rear side. Upon insertion of the 

bullet camera inside the headform, the monitor screen of the video recording unit was 

used to verify that the camera would capture current state and any change in status of the 

the warning indicator lights of the mounted thermal sensing device. The headform was 

then covered completely with a Nomex cloth head cover to protect the headform from 

heat. Once the headform was covered with the Nomex cover and a facepiece (as part of a 

self-contained breathing apparatus [SCBA] of the type typically worn by fire fighters), 

only the face of the headform (again, covered with heat resistant tape) was visible, as 

shown in the right side of Figure 2. 

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Tape 

Figure 2. The left photograph shows the headform covered with heat- resistant 

tape and drilled for bullet camera insertion. The right photograph shows the 

Nomex cloth-covered headform equipped with an SCBA facepiece and a thermal 

sensing device. 

2.2 Thermocouples 

The thermocouples used for the laboratory-scale experiments were Type K nickelChromel/nickel Alumel (Ni-Cr/Ni-Al) (Figure 3). The operating temperature range of a 

Type K thermocouple is from -269 o

C to 1260 oC. 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). The length of each thermocouple used for the laboratory-scale 

experiments was maintained at an average of 20 feet. 

Figure 3. A thermocouple as used in experiments. 

These thermocouples were attached directly to the surface of the SCBA facepiece 

and to the thermal sensing unit using heat-resistant tape and flame-resistant thread having 

a maximum diameter of 0.254 mm (0.010 in). The time constant for these 0.254 mm 

diameter bare thermocouple beads was estimated at 0.2 seconds (Omega). In order to 

ensure surface temperatures were recorded, care was taken to keep the thermocouple 

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beads in direct contact with the surface of the SCBA facepiece and of the thermal sensing 

device. 

Six thermocouples were used to record temperatures in each experiment for the 

static oven, flow loop, and radiant panel series in utilized in the laboratory-scale 

experiment matrix. The description of the location of each thermocouple is outlined in 

Table 1. The first five thermocouples were associated with the thermal sensing device or 

the SCBA facepiece. The sixth thermocouple was attached and placed at a 25.4 mm (1 in) 

distance from the thermal sensing device. This sixth thermocouple was intended for 

recording the gas (ambient) temperature close to the device. Figure 4 shows a schematic 

diagram of the location of thermocouples on the thermal sensing device and SCBA 

facepiece. 

2.3 Thermal Sensing Unit Selection and its Nomenclature 

Six thermal sensing devices were used for the laboratory-scale experiments. Each 

thermal sensing device was marked with its assigned number ranging from 1 through 6 

on the top panel in the front of each device. Five thermal sensing devices (Numbers 1, 2, 

3, 5, and 6) were instrumented with two thermocouples, one touching the front surface 

and the other touching the rear surface of each thermal sensing device in order to track 

and record the exact temperature at those surfaces. Device 6 was essentially treated as a 

‘back-up device’ in the event that any of the other devices were damaged in the 

experiment or if they malfunctioned. 

Table 1: Nomenclature for the thermocouples used in the laboratory-scale experiments. 

Thermocouple 

Label Description of Thermocouple Location Channel Name in Data Acquisition System 

TC1 

Thermocouple registering the temperature 

on the front surface of thermal sensing 

device 

TSU FT TC1 

TC2 

Thermocouple registering the temperature 

on the rear surface of the thermal sensing 

device 

TSU RR TC2 

TC3 Thermocouple registering the surface 

temperature on the inside of the facepiece FP TI TC3 

TC4 Thermocouple registering the surface 

temperature on the outside of the facepiece FP TO TC4 

TC5 Thermocouple close to the platinum sensor 

inside the Thermal sensing device TSU IE TC5 

TC6 

Thermocouple registering the ambient 

temperature at a distance of 1 inch from 

thermal sensing device attached to the 

facepiece 

TC6 

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Thermal sensing device #4 was instrumented with three thermocouples: one in 

front, one in the rear, and one inserted inside the thermal sensing device and next to the 

platinum thermal sensor to track the temperature in its vicinity. Thermal sensing device 

#4 was opened to position TC5 close to the platinum sensor itself. The thermal sensing 

device numbers, along with the manufacturer’s serial number and thermocouple 

placement, are shown in Table 2. 

Thermal Sensing Unit 

FACEPIECE 

Attachment of Device to 

Facepiece 

TC4 (inside facepiece) 

TC3 (in front of facepiece) 

TC2 and TC4 were at the same 

location, separated by facepiece 

shield. 

TC1 (in front of device) 

TC2 (in rear of device, 

and sandwiched between 

it and the facepiece shield) 

TC5 (inserted inside the device, 

next to the 

platinum sensor) 

Figure 4. Location of thermocouples on the facepiece and thermal sensing unit. 

Table 2: Nomenclature for the thermal sensing devices. 

Assigned Device 

Number 

Manufacturer’s Serial 

Number 

Thermocouple 

Specification 

TSU #1 10001629 TC1 and TC2 

TSU #2 10001708 TC1 and TC2 

TSU #3 10001638 TC1 and TC2 

TSU #4 10001623 TC1, TC2 and TC 5 

TSU #5 10001618 TC1 and TC2 

TSU #6 10001530 TC1 and TC2 

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2.4 Facepiece Selection and Nomenclature 

The thermal sensing device was interfaced with a Scott AV Face Mask 2000 

model facepiece and three such facepieces were procured for the laboratory-scale 

experiments. The manufacturer’s serial numbers along with the designated face piece 

numbers for experimental purpose are listed in Table 3. 

Table 3. 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 

Each facepiece was instrumented with two thermocouples, TC3 and TC4. TC3 

was attached to the inside surface of the facepiece, whereas TC4 was attached to the front 

surface of the facepiece. TC3 and TC4 were positioned on top of each other and 

separated by the facepiece lens. 

2.5 Digital Video Recording 

A bullet camera manufactured by Sony Electronics Inc. and powered by a 30V 

battery was used to record the status changes indicated by the warning lights of the 

thermal sensing device. The setup of the digital video recording unit is shown in Figure 

5, and the bullet camera used for recording the indicator status is shown in Figure 6. The 

video data viewed through the bullet camera was recorded onto mini-DV tapes 

manufactured by Panasonic, Inc. In order to withstand the high temperature in the 

experimental scenarios, the wire connecting the bullet camera to the battery, which 

passed through the headform and facepiece, was covered with the heat-resistant tape. 

Figure 5. The mini-DV digital video recording unit. 

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Figure 6. The Sony bullet camera used to record thermal sensing device 

indicators. 

2.6 Data Acquisition System 

The CR23X system, manufactured by Campbell Scientific Inc., and shown in 

Figure 7, is a self-contained compact data logger that measures multiple sensor types 

(such as temperature and heat flux), communicates via modems, reduces data, controls 

external devices, and stores data. The CR23X has an integral, 2-line alphanumeric 

display and power supply. A battery-backed, real-time clock and nonvolatile data storage 

is included in the system. 

Figure 7. The data logger system CR23X. 

There are 12 differential, individually configured analog inputs that were 

programmed to be used as 12 thermocouple channels for the laboratory-scale experiments 

(Campbell Scientific Inc., 1989). These 12 channels recorded the surface temperatures 

where the thermocouple bead touched. There were 3 dedicated voltage channels 

available to record the voltage or heat flux in the CR23X system, but only one of these 

three voltage channels was used. The switch connected to a battery was used to create a 

‘spike’ in real time voltage data indicating a change in status of warning lights of the 

thermal sensing device (Figure 8). This channel was referred to as the ‘marker channel.’ 

The marker channel was also used to mark certain important experiment 

parameters, such as the beginning of a experiment, the end of a experiment, and to note 

the change of warning status (e.g., from blinking green to solid green). The marker 

channel created a spike of 20 V in the data when it was actuated, leading to a change in 

status from 0 V to 20 V in the real-time data. A laptop computer, which was connected 

to the data logger system, is shown in Figure 9. The data acquisition software allow the 

temperatures to be displayed numerically and graphically in real time during each 

experiment. 

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Figure 8. Marker channel power supply and switch. 

Figure 9. Laptop computer connected to the data acquisition system. 

In order to record the temperature at each thermocouple location, the channels 

were programmed to specify the maximum temperature limit of 204 oC (400 oF) and the 

minimum temperature of -12 oC (10 oF). The data acquisition system was programmed to 

collect data every two seconds. The temperature data was an instantaneous temperature 

value; it was not averaged of 2 s and reported every 2 s. For a 30 minute experiment, the 

data system would generate approximately 900 data points. At the end of each 

experiment, the data for that experiment was labeled and stored as a separate file 

indicating the date, time, and the name of the experiment. 

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2.7 Static Oven Description 

A static oven utilizing conduction-type heat transfer was used during the first set 

of laboratory-scale experiments of the thermal sensing devices. The Static Oven (Figure 

10) was manufactured by Blue M Electric Company, and was a ‘Single Wall Transite 

Oven’ (model SW-11TA). The internal chamber dimensions were 0.30 m x 0.31m x 0.23 

m (11 in x 12 in x 9 in). The external dimensions of the oven were 0.31 m x 0.33 m x 

0.43 m (12 in x 13 in x 17 in). The internal capacity of the oven was approximately 

0.0421 m3

 (1.5 ft3). The circular thermostat knob allowed control of the temperature 

between the range of 40 oC (105 oF) to 200 oC (390 oF). The small opening on the top 

of the oven was used to insert the thermocouple wires attached to the facepiece and the 

thermal sensing device. This opening was also used to insert a glass thermometer, which 

confirmed the temperature in the oven. A thermocouple that monitored gas temperature 

was also inserted through the same opening and positioned in front of the facepiece. 

Figure 10. Static oven sealed with a temporary calcium silicate board wall/door. 

The static oven door was replaced by a temporary door made of calcium silicate 

material (Marinite I) containing a small glass viewing window whose dimensions were 

11.4 cm (4.5 in) x 29.2 cm (11.5 in). The glass window was fixed in place by four screws 

around the glass and by additional calcium silicate board. The glass viewing window 

allowed the experimenter to monitor the experiment as well as record the status change of 

the warning indicators in the thermal sensing device. 

2.8 Fire Equipment Evaluator Description 

A Fire Equipment Evaluator (FEE), which simulated convective-type heat flow, 

was used to conduct the second set of laboratory-scale experiments of the thermal sensing 

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devices. The FEE was designed and constructed to simulate moving hot gas conditions 

encountered by fire fighters. The FEE is able to reach a temperature of 300 oC with a total 

thermal flux of 20 kW/m2

, which is considered to be the radiation flux at the onset of 

flashover (Lawson et al. 1952). A functional-block diagram of the FEE is shown in 

Figure 11, and a photograph of the FEE used for experimentation is shown in Figure 12. 

Figure 11. Specifications and dimensions of a FEE tunnel (Donnelly, Davis, 

Lawson, and Selepak, 2006). 

The FEE consists of a stainless steel closed circuit flow loop and a fan driver. 

The flow loop’s dimensions are 220 cm x 174 cm x 38 cm. The test chamber of the FEE 

is 91 cm (36 in) long by 38 cm (15 in) square, and can be expanded to fit larger 

equipment specimens if needed. In case of this set of laboratory experiments, the existing 

chamber dimensions were appropriate to expose the headform along with facepiece and 

thermal sensing device. The operating conditions in the chamber included flow rates from 

0.5 m/s to 2.0 m/s. 

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Figure 12. The Fire Equipment Evaluator (FEE) flow loop. 

The operating temperature inside the chamber can be maintained up to 300 oC. 

The convective heat flux up can be programmed up to 16 kW/m2

 and the radiant flux can 

be programmed up to 4 kW/m2. The instrumentation for the FEE included thermocouples 

for temperature measurement, a bi-directional probe for velocity measurement, and flux 

gauges oriented to measure both convective and radiant flux. The photograph to the left 

in Figure 13 shows the test section of the FEE loop, and the photograph to the right 

shows the heat flow controls and graphical display of temperatures in the flow loop. 

Figure 13. The FEE test section and a display of the temperature and heat 

controls in the FEE flow loop. 

Temperature and velocity were two parameters that were controlled during the 

experimental procedures using the FEE flow loop. Temperature measurements were 

made in the test section using a ‘Type-K’ thermocouple. The flow rate was maintained at 

an average speed of 1 m/s to simulate smoke movement experienced by fire fighters in 

structural fires. 

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2.9 Radiant Panel Description 

Fire fighters’ burn injuries occur from exposures to the radiant heat energy 

produced by fire. In other cases, fire fighters can be burned by a combination of radiant 

energy and localized flame contact exposures. A radiant heat energy source was used as 

part of the laboratory-scale experiments to characterize the performance of the thermal 

sensing device under controlled and reproducible radiant heat conditions (see Figure 14). 

Figure 14. Side view of the radiant panel test apparatus (Lawson and Twilley, 

1999). 

A natural gas-fired radiant panel that is detailed in American Standards for 

Testing Materials (ASTM) standard (E 162–98) was the radiant heat source for the 

laboratory-scale experiments. The ASTM standard outlines the procedures for measuring 

and comparing the surface flammability of materials when exposed to a prescribed level 

of radiant heat energy, and is intended for measurements on materials whose surfaces 

may be exposed to fire. The rate at which the flames will travel along a surface depends 

upon the physical and the thermal properties of the material, its method of mounting and 

orientation, the type and level of fire or heat exposure, the availability of air, and the 

thermal properties of the surrounding enclosure (ASTM, 1997). 

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The experimental apparatus and its components are shown in Figure 15. The 

radiant panel consists of a porous refractory material vertically mounted in a cast-iron 

frame. A premixed air/natural gas-fueled radiant panel produces the radiant heat energy 

with a radiating surface measuring 310 mm x 460 mm (12 in x 18 in). The panel is 

equipped with a ‘venturi-type aspirator’ for mixing gas and air at approximately 

atmospheric pressure, a centrifugal blower to provide 50 L/s (100 ft3/min) air at a 

pressure of 700 Pa (2.8 in of water), an air filter to prevent dust from obstructing the 

panel pores, and a pressure regulator with a control/shut-off valve for the gas supply. 

This radiant panel is normally operated at an average surface blackbody temperature of 

670 oC ± 4 oC (1240 oF ± 7 oF). A propane gas pilot line burner allowed the researcher to 

initiate natural gas/air mixture across radiant panel width. 

Figure 15. Radiant panel assembly. 

The thermal sensing unit device was mounted on the movable trolley assembly 

and was attached to the radiant panel experiment frame as shown in Figure 16. 

Positioning of the trolley allowed for adjustment of radiant flux exposures and provided 

the ability to expose specimens to radiant energy environments that could be increased or 

decreased during the experiment (ASTM, 1997). 

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Figure 16. Side view of the radiant panel with a heat-shielding aluminum 

partition and the specimen holder mounted with a headform and facepiece. 

A calibrated Schmidt-Boelter total heat flux transducer of the type specified in 

ASTM E1321, Standard Test Method for Determining Material Ignition and Flame 

Spread Properties, was used for measuring heat flux levels (ASTM, 1997). This watercooled, thermopile type heat flux transducer had a nominal range of 0 kW/m2 to 50 

kW/m2 with a sensitivity of approximately 10 mV at 50 kW/m2. The time constant for 

this heat flux gauge was not more than 290 ms, with a corresponding time to reach 95% 

of the final output of not more than 1 s. The heat flux gauge measured 25 mm (1 in) in 

diameter and had a metal flange located 25 mm (1 in) down its body, and away from the 

sensing surface (ASTM, 1997). 

2.10 Batteries 

Thermal sensing devices operate using two AAA batteries (1.5 V, 1100 mAh). 

Prior to each exposure, the thermal sensing devices were fitted with new AAA alkaline 

batteries. Through this procedure, the potential of low battery power influencing the 

research results was minimized. 

3.0 EXPERIMENTAL PROCEDURE 

3.1 Experimental Exposure Matrix 

Six thermal sensing units were utilized during the three sets of laboratory-scale 

experiments. The exposures were designed to simulate the following conditions that fire 

fighters experience: 

1) Static Oven Experiments representing the conductive heat effects of working in a

hot environment, 

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2) Fire Equipment Evaluator Experiments to recreate the convective heat flow when

moving through a hot environment or when having smoke and hot gases flow past

a fire fighter, and

3) Radiant Panel Experiments representing exposure to significant thermal heat flux

as experienced by a fire fighter in a burning room or under a flaming upper layer.

Repeatability and reproducibility were incorporated into the experiment regimen

for the three sets of laboratory experiments. In order to examine the performance of the 

thermal sensing device through reproducibility, a particular device was exposed three 

times within the same experiment conditions. Conducting three repetitions also helped to 

spotlight any ‘abnormal performance’ that might have presented during one of the three 

experiments, such as a specimen malfunction. Thermal sensing device 5 (TSU #5) was 

selected for experimenting under this protocol for not only the laboratory-scale 

experiments, but also for the full-scale experiments described in a second report 

(Deshmukh et al. 2013). In order to validate the repeatability of a range of thermal 

sensing devices in identical experimental conditions for the laboratory-scale experiments, 

five devices were selected. Four devices (TSU #1, TSU #2, TSU #3, and TSU #6) were 

instrumented identically, whereas device 4 (TSU #4) was instrumented with an additional 

thermocouple close to the platinum sensor and inside the device. This research plan for 

reproducibility and repeatability is shown in Tables 4 and 5. 

Table 4: Research plan to examine the reproducibility of the thermal sensing device. 

Description Static Oven Fire Equipment Radiant Panel 

Evaluator Flux 1 Flux 2 

TSU # 5 – 

Experiment 1 

Repetition 1 Repetition 1 Rep 1 Rep 1 

TSU # 5 – 

Experiment 2 

Repetition 2 Repetition 2 Rep 2 Rep 2 

TSU # 5 – 

Experiment 3 

Repetition 3 Repetition 3 Rep 3 Rep 3 

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Table 5. Research plan to examine the repeatability of the thermal sensing device. 

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Description Static Oven Fire Equipment Radiant Panel (RP) 

(SO) Evaluator (FEE) Flux 1 Flux 2 

Experiment 1 – TSU 

# 1 

SO­ 1 FEE- 1 RP- 1 RP- 1 

Experiment 2 – TSU 

# 2 

SO­ 2 FEE­ 2 RP­ 2 RP­ 2 

Experiment 3 – TSU 

# 3 

SO­ 3 FEE­ 3 RP­ 3 RP­ 3 

Experiment 4 – TSU 

# 4 

SO­ 4 FEE­ 4 RP­ 4 RP­ 4 

Experiment 5 – TSU 

# 6 

SO­ 5 FEE­ 5 RP­ 5 RP­ 5 

As mentioned earlier, the data set from thermal sensing device 6 (TSU #6) has 

been treated as a ‘replacement dataset’ should any of the other devices fail. Overall, 

there were seven Static Oven experiments, seven FEE experiments, and 14 Radiant Panel 

experiments at two different flux levels. Also as mentioned in the earlier discussion, 

radiation is a very efficient mode of energy transfer that may cause varying damage to the 

devices within a very short span of time. Two different heat flux levels were selected and 

executed at the end of the laboratory-scale experiments, after completion of the Static 

Oven and FEE experiments. 

3.2 Procedure for Laboratory Experiments 

Before beginning any of the laboratory-scale experiments, certain procedures 

needed to be followed in the form of a ‘checklist’ in an effort to reduce or eliminate 

variability. Once the ‘pre-experiment checklist’ was completed, another checklist, 

‘during experiment checklist’ was initiated. A third checklist was consulted after the 

completion of a particular experiment. 

3.2.1 Static Oven Experiment Procedure 

The headform with a facepiece installed with the sensing device, was mounted in 

the center of the static oven using the wires as shown in Figure 17. Four pieces of wire 

were used to suspend the facepiece in the center of the oven by tying them to the steel 

rods that were attached to the oven’s interior sides. A rectangular heat-resistant tile was 

placed below the base of the headform in order to insulate the headform from direct heat. 

A glass thermometer was inserted through the small opening in the roof of the oven to 

track temperatures during the experiment. The modified insulating board oven door was 

closed. 

The power was set to ON for the oven and the thermostat was set at 50 o

C. Upon 

achieving an oven temperature of 50 o

C, the experiment start time was recorded in the 

laboratory notebook, and the marker channel was actuated to create a spike in the voltage 

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data that was recorded. The temperature was increased at an interval of 10 oC every 3 

minutes by turning the thermostat knob. While the temperature in the oven was 

increasing, any change in status of the indicator lights was recorded by actuating the 

marker channel and also recording each event in the laboratory notebook. The 

temperature in the oven was increased until it reached 140 oC. A record was made in the 

laboratory notebook when the thermal sensing device displayed blinking red lights, 

indicating that the environment was ‘still heating.’ The static oven was turned off once 

the temperature reached 140 oC. 

Figure 17. Instrumented setup for the static oven experiment. 

The modified door panel was opened and a cooling fan was directed toward the facepiece 

for rapid cooling. The bullet camera and the experiment specimen were allowed to cool 

for at least 15 minutes at the end of each experiment. After the exposure series was 

completed for each specific thermal sensing unit, it was removed from the oven and the 

next device to be exposed was mounted in the oven. Before initiating the next 

experiment series, each wiring connection and thermocouple readout was verified. The 

static oven experiment was repeated using different sensing devices to complete the 

experimental matrix. Eight experiments were completed over a period of two days in this 

manner. In the first pilot experiment, the bullet camera overheated, leading to melting of 

an exposed portion of the bullet camera at the maximum temperature of 140 o

C. As a 

result, all future experimenting in the static oven was halted at 140 oC. 

3.2.2 Fire Equipment Evaluator Experiment Procedure 

A thermocouple inside the experiment section area of the FEE was monitored to 

confirm ambient gas temperature. This temperature was used as the reference 

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temperature for the experimental trial. The headform covered with the instrumented 

facepiece and the thermal sensor device was mounted in the center of the FEE’s flow 

section. The headform was suspended in the center of the flow section using four small 

wires which were tied to steel rods attached to the walls of the flow section (similar to 

that of the static oven experiments, see Figures 18 and 19). The thermocouple 

connections were verified to ensure that the data acquisition system was reading all 

temperatures. The door of the test area of the FEE was closed and the temperature was 

increased to 50 oC. The experiment was started once the temperature of 50 oC was 

achieved. The experiment start time was recorded in the laboratory notebook and the 

marker channel was actuated. The temperature inside the FEE flow loop was increased at 

an interval of 10 o

C every 3 minutes from the experiment start time (to simulate a gradual 

heating environment as in a real fire scenario). Changes in the status of the indicator 

lights were recorded by actuating the marker channel as well as by recording the 

temperature and time in the laboratory notebook. In order to be consistent with the static 

oven experiment maximum temperature limit, the temperature in the FEE was also 

increased until it reached 140 oC. The FEE heater controls were turned off once the test 

area’s temperature reached 140 o

C. The thermal sensing device as well as the bullet 

camera were allowed to cool for fifteen minutes. The door of the test area was opened 

and the headform, facepiece, and thermal sensing device were removed. The FEE 

experiment was repeated using different thermal sensing devices to complete the research 

procedure. Eight FEE experiments were conducted over a period of two days, and the 

timeline for each experiment is listed in the results section. 

Figure 18. Instrumented setup for the Fire Equipment Evaluator experiment. 

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3.2.3 Radiant Panel Experiment Procedure 

Before conducting a radiant panel experiment, a radiant heat source calibration 

was necessary. First, the thermal environment (heat flux of 1.6 kW/m2) was selected for 

the first set of experiments. The gas-fired radiant panel was ignited and was allowed to 

preheat for 45 minutes. The preheat time allowed stabilization of the radiant panel 

temperature before calibration was attempted. Using the calibration curve for the 

Schmidt-Boelter heat flux gauge, the millivolt output value was calculated for the 

selected incident heat flux. In order to achieve a uniform and steady heat flux, the radiant 

panel was calibrated each day prior to conducting experiments. 

For the first set of experiments using radiant panel, a flux of 1.6 kW/m2 was 

chosen as the target flux (i.e., the heat flux that fire fighters face while fighting a fire and 

that they can survive in for 30 minutes or less without developing skin burns (National 

Fire Protection Association (NFPA), 1971). To achieve a flux of 1.6 kW/m2, the 

specimen holder was positioned at a distance of 83.8 cm (33 in) from a reference point of 

the radiant panel. A set of three aluminum panels was used to shield the thermal sensing 

device from the radiant heat while the headform, along with the instrumented facepiece, 

was mounted on the specimen-carrying movable frame (Figure 19). The headform and 

facepiece were mounted in the center of the movable frame such that the heat from the 

radiant panel was incident on the sensing device. The headform was tilted and tightened 

at an angle as shown in Figure 20, resulting in the thermal sensing device positioned 

parallel to the radiant panel. In order to secure the headform in the desired location and 

inclination, two small wires attached to the facepiece were tied to steel frames. 

Figure 19. Side view of the radiant panel with a heat-shielding aluminum panels and the 

specimen holder mounted with a headform and facepiece. 

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The exposure was initiated by removing the heat shield and recording the time in 

the laboratory notebook and on the marker channel. Once the warning indicators on the 

thermal sensing unit demonstrated a continuous blinking red indicator, the thermal shield 

was inserted between the radiant panel and the facepiece. The movable specimen holder 

was moved away from the radiant panel to allow it to cool for fifteen minutes. The next 

device and facepiece were mounted for the next experiment. Eight experiments were 

repeated in the same fashion as above at a flux intensity of 1.6 kW/m2. A set of 

experiments was repeated at a flux intensity of 4 kW/m2

. In order to achieve the target 

flux level of 4 kW/m2, the mask mounted with the thermal sensing unit, positioned on the 

movable trolley, was hooked at a distance of 40.6 cm (16.0 in) from the radiant panel. 

Changes in status of indicator lights were recorded in the laboratory notebook as well as 

by actuating the marker channel. The timeline for each experiment is listed in the results 

section. 

Figure 20. Instrumented setup for the Radiant Panel experiments. 

4.0 RESULTS 

4.1 Thermal Environment for Static Oven, FEE, and Radiant Panel Experiments 

Figure 21 displays the thermal environment inside the static oven in which the 

situational awareness devices were examined across several thermocouple (TC) locations. 

TC6 recorded the ambient temperature during each experiment. The graph in Figure 21 

shows the rate of increase of temperature per second for each static oven experiment. It 

indicates the maximum temperatures that the various thermal sensing units were exposed 

to in the enclosed static oven environment. Figure 22 shows the thermal environment 

inside the Fire Equipment Evaluator 

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In the case of the Radiant Panel experiments, the experiments were conducted in a 

laboratory without any enclosed environment as in Static Oven or FEE. The thermal 

environment in the radiant panel experiments is shown in Figure 23 and Figure 24. 

4.2 Static Oven Experiment Results 

Table 6 outlines the performance of various thermal sensing devices within the Static 

Oven, and Table 7 presents the same information for thermal sensing device (TSU #5). 

Figure 25 displays the graphical representation of the warning indicators of various 

thermal sensing devices in the Static Oven experiment, whereas Figure 26 shows the 

graphical representation of the warning indicators of unit 5 (TSU #5) in three Static Oven 

experiments. 

Table 6. Performance of different devices in the Static Oven experiments. 

Device # Blinking 

Green (oC) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #1 64 No Status 99 113 

TSU #2 83 No Status 123 135 

TSU #3 75 90 91 109 

TSU #4 65 114 No Status 120 

TSU # 6 56 91 90 102 

Table 7. Performance of thermal sensing device #5 in the Static Oven experiments. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #5 – Rep 1 58 86 90 109 

TSU #5 – Rep 2 73 90 105 110 

TSU #5 – Rep 3 53 79 82 94 

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Figure 21. Thermal Environment in Static Oven experiments.

TSU2 TSU6 TSU5R3 

TSU3 TSU5R1 

TSU4 TSU5R2
 

150
 

120
 

90
 

60
 

30
 

0
 

0 300 600 900 1200 1500 1800
 

Time, s
 

Figure 22. Thermal Environment in FEE experiments. Temperature, oC 

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TSU2 TSU6 TSU5R3 

TSU3 TSU5R1 

TSU4 TSU5R2 

150 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 1500 1800 

Time, s 

Figure 23. Thermal Environment in Radiant Panel experiments at heat flux of 1.6 kW/m2. 

TSU2 TSU6 TSU5R3 

TSU3 TSU5R1 

TSU4 TSU5R2 

150 

120
 

Temperature, oC 

90 

60 

30 

0 

0 300 600 900 1200 1500 1800 

Time, s 

Figure 24. Thermal Environment in Radiant Panel experiments at heat flux of 4.0 kW/m2.

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Figure 25. Measured onset temperature of sensors indicators for repeat 

experiments in the static oven series. 

Figure 26. Measured onset temperature of device 5 (TSU #5) indicators for repeat 

experiments in the static oven series. 

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4.3 Fire Equipment Evaluator Experiment Results 

Table 8 presents the results for the display indicator light conditions as a function 

of temperature, and Table 9 presents the same data for device 5 (TSU #5). Figure 27 

displays the graphical representation of the warning indicators of various devices in the 

FEE experiment, whereas Figure 28 shows the graphical representation of the warning 

indicators of device 5 (TSU #5) in three FEE experiments. 

As shown in Table 8 and Figure 26, device 1 (TSU #1) ceased to function in the 

FEE experiment. 

Table 8. Performance of different devices in the FEE experiments. 

Device # Blinking 

Green (oC) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #1 No Status No Status No Status No Status 

TSU #2 50 84 87 92 

TSU #3 60 100 108 118 

TSU #4 65 105 107 107 

TSU #6 59 102 108 119 

Table 9. Performance of thermal sensing device # 5 in three repetitions of the FEE 

experiment. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #5 – Rep 1 62 104 111 131 

TSU #5 – Rep 2 61 106 110 121 

TSU #5 – Rep 3 67 107 114 120 

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Figure 27. Measured onset temperature of sensors indicators for repeat experiments in

the FEE experiments. 

Figure 28. Measured onset temperature of device 5 (TSU #5) indicators for repeat 

experiments in the FEE series. 

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4.4 Radiant Panel Experiment Results 

Table 10 presents the results for the display indicator light conditions as a 

function of temperature, and Table 11 presents the same data for device 5 (TSU #5). 

Figure 29 displays the graphical representation of the warning indicators of various 

devices in the Radiant Panel experiment at a heat flux level of 1.6 kW/m2 , whereas 

Figure 30 shows the graphical representation of the warning indicators of device 5 (TSU 

#5) in three Radiant Panel experiments at a heat flux of 1.6 kW/m2

. 

Table 10: Performance of different devices in radiant panel experiments at a heat 

flux of 1.6 kW/m2

. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #2 44 87 88 96 

TSU #3 48 57 62 58 

TSU #4 61 85 86 89 

TSU #6 39 40 38 40 

Table 11: Performance of thermal sensing device #5 in radiant panel experiments at a 

heat flux of 1.6 kW/m2

. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #5 – Rep 1 55 72 73 77 

TSU #5 – Rep 2 59 85 87 94 

TSU #5 – Rep 3 62 87 87 89 

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Figure 29. Measured onset temperature of sensors indicators for repeat experiments in 

the Radiant Panel series at a heat flux of 1.6 kW/m2

. 

Figure 30. Measured onset temperature of device 5 (TSU #5) indicators for repeat 

experiments in the Radiant Panel series at a heat flux of 1.6 kW/m2. 

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Table 12 presents the results for the display indicator light conditions as a 

function of temperature, and Table 13 presents the same data for device 5 (TSU #5). 

Figure 31 displays the graphical representation of the warning indicators of various 

thermal sensing devices in the Radiant Panel experiment at a heat flux of 4.0 kW/m2 , 

whereas Figure 32 shows the graphical representation of the warning indicators of device 

5 (TSU #5) in three Radiant Panel experiments at a heat flux of 4.0 kW/m2. 

Table 12: Performance of different devices in the radiant panel experiments at a heat flux 

of 4.0 kW/m2. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #2 44 69 81 99 

TSU #3 67 90 97 101 

TSU #4 74 101 107 126 

TSU #6 43 45 47 48 

Table 13: Performance of thermal sensing device #5 in the radiant panel experiments at a 

heat flux of 4.0 kW/m2

. 

Device # Blinking Green 

(

o

C) 

Solid Green 

(

o

C) 

Solid Red 

(

o

C) 

Blinking 

Red (oC) 

TSU #5 – Rep 1 78 109 112 117 

TSU #5 – Rep 2 81 103 109 115 

TSU #5 – Rep 3 83 102 105 107 

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Figure 31. Measured onset temperature of sensors indicators for repeat 

experiments in the Radiant Panel series at a heat flux of 4.0 kW/m2. 

Figure 32. Measured onset temperature of device 5 (TSU #5) indicators for repeat 

experiments in the Radiant Panel series at a heat flux of 4.0 kW/m2

. 

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5.0 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 14. 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 air temperature measurements includes radiative cooling in 

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

located inside the facepiece. Gas temperature measurements were monitored up 140 oC. 

There were no temperature fluctuations of large magnitude and typically the temperature 

was incremented 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 panel could had radiated some energy to the 

thermocouple bead and this could have cause 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 -15 % to +12 % total 

expanded uncertainty for the laboratory-scale experiments. 

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 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, positioning or locating instrumentation 

such as thermocouples or heat flux gauges was estimated to have the lowest total 

expanded uncertainty of ± 11 %. 

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Table 14: Uncertainty in lab scale experimental data. 

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Component 

Standard 

Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

Air Temperature 

Calibration ± 1 % 

 Radiative Cooling - 5 % to + 0 % - 8 % to + 6 % - 15 % to + 12 % 

Radiative Heating - 0 % to + 2 % 

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 evaluation efforts for the situational awareness device in the controlled, 

laboratory-scale experiments provided significant operational data. Systematic test 

methods involving conduction, convection, and radiation types of heat transfer were used 

to evaluate the performance of the thermal sensing units in one or a combination of the 

three heat transfer conditions. 

6.1 Static Oven Experiments 

The first method of laboratory-scale experimentation was that of the Static Oven, 

which represented the conduction-type of heat transfer. The Static Oven environment 

was able to achieve a maximum temperature of 140 o C. Although the thermostat knob 

was manipulated carefully in an effort to increment the oven temperature by 10 oC every 

three minutes, the rate of temperature increase was not uniform, and this contributed to 

the uncertainty in the warning indicator response/activation temperature. The Static 

Oven experiments provided data indicating that the thermal sensing device could 

withstand static, hot conditions at temperatures up to 140 oC. 

The repeatability of the ‘blinking green’ indicator light across the six thermal 

sensing devices that was examined with respect to temperature was not uniform. The 

‘blinking green’ indicator was noted to actuate throughout a large range of temperatures, 

from 56 o

C to 83 oC. Thermal sensing devices #1 and #2 did not display the ‘solid green’ 

indicators at all, whereas other devices displayed the ‘solid green’ warning indicator for a 

short period of time, again across a wide range of temperatures from 90 oC to 114 oC, 

before transitioning to ‘solid red’ indicators. The ‘solid red’ indicator was mixed with 

respect to the temperature at which it actuated between devices, ranging from 90 oC to 

123 oC, and TSU #4 did not present a ‘solid red’ indicator at all. Finally, the ‘blinking 

red’ indicator activated across all thermal sensing devices while the environment was 

cooling, during the experiments used to examine device repeatability. They did so across 

a wide range of temperatures between 102 oC to 135 oC. These results suggest that 

repeatability between thermal sensing devices may be spread over a large a range of 

temperatures. 

The reproducibility for the ‘blinking green’ indicator was also not uniform, but to 

a lesser extent, from 53 o

C to 73 oC. Thermal sensing device #5 was noted to produce 

‘solid green’, ‘solid red’, and ‘blinking red’ indicators at temperature ranges of 79 oC to 

90 oC, 82 oC to 105 oC, and 94 oC to 110 oC, respectively. These data indicate that, for 

the same device exposed multiple times, there are issues of reproducibility with respect to 

the actuation of the various TSU indicators within the Static Oven. 

6.2 Fire Equipment Evaluator Experiments 

The second method of laboratory-scale examination was that of the Fire 

Equipment Evaluator, which represented the convective-type of heat transfer. The FEE 

was able to create a temperature environment in the range of 130 o

C to 140 oC at a steady 

velocity of 1 m/s and a heat flux of 4 kW/m2. It should be noted that thermal sensing 

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device #1 failed to display any warning indicators during the FEE experiment, suggesting 

problems with the unit not functioning properly. The ‘blinking green’ indicator of the 

other five thermal sensing devices under identical experiment conditions (i.e., 

repeatability) was noted to actuate throughout a 15 oC range of temperatures, from 50 oC 

to 65 oC. The ‘solid green’ indicator was observed to actuate across a wide range of 

temperatures between 84 oC to 105 oC. The repeatability of the ‘solid red’ indicator was 

quite consistent (i.e., 107 oC to 108 oC) with the exception of TSU #2, with its actuation 

occurring at a temperature of 89 o C. Finally, the ‘blinking red’ indicator was noted to 

activate across a wide range of temperatures, between 92 oC to 119 oC when the 

environment began to cool. Again, the variability of status indicators with respect to the 

temperatures at which they actuated across devices suggests further issues of 

repeatability. 

With respect to reproducibility in the FEE experiments, the ‘blinking green’ 

indicator was noted to actuate between 62 oC to 66 oC. The ‘solid green’ indicator was 

reasonably consistent, ranging from 104 oCto 107 oC. The reproducibility of the ‘solid 

red’ indicator was reasonably consistent, ranging from 110 oC to 114 oC across three 

trials, and finally, the ‘blinking red’ indicator was noted to activate between the 

temperatures of 120 oC to 131 oC when the environment began to cool. These results 

suggest reasonable reproducibility of a particular thermal sensing device under 

convective conditions. 

6.3 Radiant Panel Experiments 

The third method of laboratory-scale experimentation was that of the Radiant 

Panel, which represented the radiation-type of heat transfer. As explained earlier, 

radiation is and efficient mode of energy transfer and under fire conditions can represent 

a serious thermal source to which a fire fighter can be exposed. The Radiant Panel 

experiments were conducted at two radiant heat flux levels: 1.6 kW/m2

 and 4.0 kW/m2. 

Any heat flux more than 1.4 kW/m2 but less than 2.5 kW/m2 has been described as a 

‘common thermal radiation exposure’ while firefighting (Donnelly et al., 2006). This 

energy level may cause burn injuries with prolonged exposure. An exposure of more than 

2.5 kW/m2 but less than 4.5 kW/m2 can cause the skin to become blistered with a 30 s 

exposure, causing a second-degree burn injury (National Fire Protection Association 

(NFPA), 1971). Therefore, the two flux levels selected for the Radiant Panel experiments 

represented realistic fire exposures to which fire fighters and their protective gear are 

routinely exposed. 

Even though the Radiant Panel experiments were not able to reach the 

temperatures of more than 100 o

C to 110 oC at the heat flux of 1.6 kW/m2 (and as 

described previously), the thermal sensing devices responded rapidly for radiant heat 

exposures at room temperature as the radiant panel was not an enclosed device. Within 

the heat flux of 1.6 kW/m2

 and with respect to repeatability, the ‘blinking green’ indicator 

of the thermal sensing devices varied between 39 oC to 61 oC. The ‘solid green’ 

indicators were observed to actuate between 40 o

C to 87 oC, and the ‘solid red’ indicators 

actuated within the range of 37 oC to 88 oC. The ‘blinking red’ indicator was noted to 

display in the range of 40 oC to 96 oC when the environment began to cool. Thermal 

sensing devices #2 and #4 appeared to perform similarly for many indicator conditions; 

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however, thermal sensing devices #3 and especially #6 performed quite differently when 

compared to the others across all indicators, suggesting issues of repeatability. 

With respect to reproducibility of the thermal sensing device in the Radiant Panel 

experiments that were conducted in a heat flux of 1.6 kW/m2, the performance of TSU #5 

was largely consistent between 55 oC to 61 oC for display of the ‘blinking green’ 

indicators. The ‘solid green’ indicator was noted to actuate between 72 oC to 87 oC, and 

the ‘solid red’ indicator actuated between 73 oC to 87 oC. Finally, the ‘blinking red’ 

indicator activated between the temperatures of 77 o

C to 95 oC when the environment 

began to cool. As one would expect the same device to present status indications at the 

same or similar temperatures, these results suggest issues of reproducibility within the 

heat flux level examined. 

The thermal sensing devices responded most rapidly to the heat flux level of 4.0 

kW/m2. Typically, the thermal sensing devices started displaying the ‘blinking green’ 

indicator within 3 minutes of Radiant Panel exposure. The Radiant Panel experiments at 

this flux exposure were noted to result in the shortest duration of time (12 minutes) for 

the devices to display all of the warning indicators (i.e., from ‘blinking green’ to 

‘blinking red’) when compared to the earlier heat flux of 1.6 kW/m2

. With respect to 

repeatability, the ‘blinking green’ indicator performance was noted to occur between the 

temperatures of 43 oC to 74 oC. The ‘solid green’ indicators were observed to actuate 

between 45 oC to 101 oC, and the ‘solid red’ indicator actuated between the temperatures 

of 47 o C to 107 oC. Finally, the ‘blinking red’ indicator was noted to actuate between 

the temperatures of 48 o

C to 126 oC. The ranges of temperature at which all status 

indicators were actuated across devices appear to be quite large, suggesting issues of 

repeatability for this rate of heat flux. 

The reproducible performance of the device within the heat flux of 4.0 kW/m2 

was largely consistent, with the ‘blinking green’ indicator actuating between 78 oC to 83 o

C. For the ‘solid green’, ‘solid red’, and ‘blinking red’ indicators, the temperatures at 

which they were noted to actuate were between 102 oC to 106 oC, 105 oC to 112 oC, and 

107 o

C to 117 oC, respectively. The temperature ranges for actuation of the warning 

indicators appears to be small, at least when compared to the lower heat flux level 

examined, suggesting that the thermal sensing device maintained reasonable 

reproducibility at the 4.0 kW/m2 exposure. This is quite different than the reproducibility 

at the lower flux of 1.6 kW/m2 exposure. 

7.0 CONCLUSIONS 

A total of seven Static Oven experiments and seven FEE experiments were 

conducted. Two sets of seven experiments were conducted at two different heat flux 

using the Radiant Panel (i.e., fourteen total experiments). The experiments were 

conducted to examine performance of personal situational awareness tools/devices 

designed for fire fighters in conductive-, convective-, and radiation-type heat transfer 

conditions. The results from these laboratory-scale experiments produced warning 

indicators that actuated across a wide range of temperatures, and the extensive digital 

video footage that was captured of the thermal sensing device’s performance in these 

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varying heat conditions provided evidence to this effect. The range of temperatures 

catalogued from these experiments, of both a repeatable and a reproducible nature, 

suggest that there are issues related to both types of criteria. That is, one would expect 

the same device to present data that was consistent across trials (i.e., reproducible), and 

one would further expect multiple devices comprised of identical components to present 

data that was consistent between them (i.e., repeatable). Among the various experiments 

employed, the thermal sensing device exhibited some inconsistencies in performance that 

give rise to questioning its reproducibility and/or repeatability under certain conditions. 

A limited series of thermal exposure experiments in a static oven, a heated flow 

loop, and a radiant panel provide performance data for thermal sensing technology. 

Laboratory 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. These thermal exposures were designed to 

simulate a fire fighter standing in a hot room (static oven), a fire fighter moving through 

smoke (heated flow loop), and a fire fighter exposed to a flaming heat source (radiant 

panel). In each scenario, the thermal sensing units survived the thermal conditions, 

tracked the gas temperatures, and provided the user with a visual display linked to the 

thermal conditions. The display of solid or blinking green and red LEDs provided the 

user with real time update as to the changing thermal conditions. 

During thermal exposures, gas temperatures 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 

differences in thermal conditions from the static oven, heated flow loop, and the radiant 

panel. These thermal sensing units responded in a similar manner whether in the static 

oven, heated flow loop, or radiant panel. This suggests that this implementation of 

thermal sensing technology would 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 situational awareness technology 

in each of the scenarios. Standard testing protocols need to include conduction-, 

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

exposed to all three scenarios. While these laboratory scale exposure allow the 

conditions to be carefully controlled, there will still be a need to conduct full-scale 

experiments in order to ensure the technology performs under real fire conditions. 

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 not predict future conditions. In this work, 

a thermal sensing unit can detect the change from previous thermal conditions, but it 

can’t 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. 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. 

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

awareness technology be able to survive and function in the range of conditions that fire 

fighters experience. Representative performance metrics and standard testing protocols 

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. 

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Surface Flammability of Materials Using a Radiant Heat Source, Annual Book of 

ASTM Standards, Vol. 04.07, West Conshohocken, PA. 

American Society for Testing and Materials,(1997). E 1321 - Standard Test Method for 

Determining Materials Ignition and Flame Spread Properties, Annual Book of 

ASTM Standards, Vol. 04.07. West Conshohocken, PA: American Society for 

Testing and Materials. 

Bretschneider, N., Brattke, S. & Rein, K. (2006). Head mounted displays for fire fighters. 

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Bremen Germany. 

Babrauskas V., (2002). Heat Release Rates, The SFPE Handbook of Fire Protection 

Engineering, 3rd Edition (Section 3, Chapter 1), National Fire Protection 

Association and The Society of Fire Protection Engineers, Quincy, MA, P.J. 

DiNenno, D.Drysdale, C.L. Beyler, and W.D. Walton, eds., pp.1-37. 

Bryant, R.A., Ohlemiller, T.J., Johnsson, E.L., Hamins, A., Grove, B. s., Guthrie, W.F., 

Maranghides, A., Mulholland, G.W. (2004). The NIST 3 Megawatt Quantitative 

Heat Release Rate Facility – Description and Procedures NISTIR 7052, 

Gaithersburg, MD: National Institute of Standards and Technology. 

Campbell Scientific, Inc., (1989). CR 23X Datalogger Operator’s Manual, Logan Utah: 

Campbell Scientific. 

Deshmukh, A., Casali, J. G., Lancaster, J.A., Bryner, N.P., McLane, R.A. (2013). 

Thermal Exposure Sensor for Fire Fighters-Full-Scale Performance Experiments, 

NIST Technical Note XXXX, Gaithersburg, MD: National Institute of Standards 

and Technology. 

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Donnelly, M.K., Davis, W.D., Lawson, J.R., Selepak, M.J. (2006). Thermal Environment 

for Electronic Equipment used by First Responders, NIST Technical Note 1474, 

Gaithersburg, MD: National Institute of Standards and Technology. 

Dillon, S. E. (1998). Analysis of the ISO 9705 Room /Corner Test: Simulations, 

Correlations and Heat Flux Measurements, NIST-GCR-98-756, Gaithersburg, 

MD: National Institute of Standards and Technology. 

Lawson, D.I., and Simms, D.L.,(1952). The ignition of Wood by Radiation, British 

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Lawson, J. Randall, and Twilley, W. H. (1999). Development of an Apparatus for 

Measuring the Thermal Performance of Fire Fighters’ Protective Clothing, 

NISTIR 6400, Gaithersburg, MD: National Institute of Standards and 

Technology. pp 1-52. 

Omega Engineering, Thermocouple Response Timehttp://www.omega.com/temperature/Z/ThermocoupleResponseTime.html 

National Fire Protection Association (1971), Standard on Protective Ensemble for 

Structural Fire Fighting, 1997 Edition, Quincy, MA: National Fire Protection 

Association, 

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