NIST Technical Note 1499 

Performance Metrics for Fire Fighting Thermal 

Imaging Cameras – Small- and Full-Scale 

Experiments 

Francine Amon 

Nelson Bryner 

Andrew Lock 

Anthony Hamins 

Sponsored in part by 

Department of Homeland Security

National Institute of Standards and Technology 

U.S. Department of Commerce 

i 

NIST Technical Note 1499 

Performance Metrics for Fire Fighting Thermal Imaging 

Cameras – Small- and Full-Scale Experiments

Francine Amon 

Nelson Bryner 

Andrew Lock 

Anthony Hamins 

Fire Research Division 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-8661 

July 2008 

Department of Homeland Security 

Michael Chertoff, Secretary 

Federal Emergency Management Agency 

R. David Paulison, Administrator 

United States Fire Administration 

Gregory Cade, Fire Administrator 

U.S. Department of Commerce 

Carlos M.Gutierrez, Secretary 

National Institute of Standards and Technology 

James Turner, Acting Director 

ii 

ABSTRACT 

Thermal imaging cameras (TIC) are becoming an important tool for many firefighters and other 

first responders. However, due to the lack of performance standards for TIC, a wide variety of 

designs and capabilities are provided to end users with little consistency in reported performance. 

In order to understand the performance characteristics of TIC during fire fighting applications, it 

is critical that a set of performance metrics and standard testing protocols be developed to allow 

the fire service to evaluate TICs. The National Institute of Standards and Technology (NIST) 

has been conducting research to characterize and understand TIC performance. This work began 

with an assessment of the thermal imaging needs and activities of first responders. Existing 

standards were collected and reviewed to ensure that the recommended testing conditions in this 

work are consistent with standards on other first responder equipment that are exposed to similar 

operating conditions, as well as standards and test protocols on infrared cameras that are used in 

other applications, when appropriate. A survey of the literature was also performed to explore 

existing work in which the fire environment was well characterized and pertinent to TIC testing. 

The consolidation of all of this information, e.g., first responder feedback, literature search, and 

full- and bench-scale testing results, provided a basis for defining testing conditions that 

challenge TIC in meaningful ways. Performance metrics that describe TIC image contrast, 

effective temperature range, spatial resolution, image nonuniformity, and thermal sensitivity 

were selected or developed, based on an analysis of the information gathered. These imaging 

performance metrics and test methods have been provided to standards development 

organizations, such as National Fire Protection Association (NFPA) and ASTM International. 

NFPA’s Technical Committee on Electronic Safety Equipment has incorporated these metrics 

and test protocols in a draft version of NFPA 1801, Standard on Thermal Imagers for the Fire 

Service, which is currently in the public proposal phase. 
iii 

ACKNOWLEDGEMENTS 

Funds for this project have been provided by the Department of Homeland Security (DHS), the 

United States Fire Administration (USFA), the Office of Law Enforcement Standards (OLES), 

Advanced Fire Service Technology Program (NIST) and Advanced Technology Program 

(NIST). Mr. William Troup (USFA), Mr. Philip Mattson (OLES), and Mr. Nicholas Paulter 

(OLES) provided valuable input as contract monitors. 

For their effort and participation in conducting the modeling and experimental work, the authors 

would like to thank Marc Nyden, Justin Rowe, Josh Dinaburg, Chang Bo Oh, Yong Shik Han, 

Sung Chan Kim, Gwon Hyun Ko, Roy McLane, and Jay McElroy. 

The authors would also like to thank the participants of the Workshop on Thermal Imaging 

Research Needs for First Responders for their expertise, insight, and willingness to provide their 

input. 

The authors express their special appreciation to Gerald C. Holst of JCD Publishing for 

providing technical advice and encouragement throughout this project. 
iv 

DISCLAIMER 

Certain companies and commercial properties are identified in this paper in order to specify 

adequately the source of information or of equipment used. Such identification does not imply 

endorsement or recommendation by the National Institute of Standards and Technology, nor 

does it imply that this source or equipment is the best available for the purpose. 

 
v 

TABLE OF CONTENTS 

1. INTRODUCTION ................................................................................................................ 11

1.1. Approach ........................................................................................................................ 12

2. BACKGROUND .................................................................................................................. 13

2.1. Imager design ................................................................................................................. 13

2.2. Detector technologies ..................................................................................................... 15

2.3. Operating environment ................................................................................................... 19

2.4. Performance metrics ....................................................................................................... 19

3. WORKSHOP ON THERMAL IMAGING RESEARCH NEEDS FOR FIRST 

RESPONDERS ............................................................................................................................. 21

4. SURVEY OF RELEVANT STANDARDS AND WORK BY OTHERS ............................. 23

4.1. Relevant standards .......................................................................................................... 23

4.2. Work by others ............................................................................................................... 24

4.3. TIC operations ................................................................................................................ 26

5. INFORMATION CONSOLIDATION- TEST CONDITIONS ............................................. 27

5.1. Series 1 test facility ........................................................................................................ 27

5.2. Series 2 test facility ........................................................................................................ 30

5.3. FTIR measurements ....................................................................................................... 33

5.4. Hose stream experiments ............................................................................................... 34

5.5. Full-scale experimental results ....................................................................................... 35

5.5.1. Heat effects ............................................................................................................. 37

5.5.2. Smoke effects .......................................................................................................... 41

5.5.3. FTIR measurement results ...................................................................................... 43

5.5.4. Hose stream results ................................................................................................. 44

5.6. Consolidation of test condition information ................................................................... 47

6. PERFORMANCE METRICS AND TEST METHODS ...................................................... 50

6.1. Image Recognition Procedure ........................................................................................ 50

6.2. Image capturing procedure ............................................................................................. 52

6.3. Contrast .......................................................................................................................... 52

6.4. Effective temperature range (ETR) ................................................................................ 54

6.5. Nonuniformity ................................................................................................................ 56

6.6. Spatial resolution ............................................................................................................ 59

6.7. Thermal Sensitivity ........................................................................................................ 61

7. RESULTS AND DISCUSSION ............................................................................................ 63

7.1. Contrast and ETR ........................................................................................................... 63

7.2. Nonuniformity ................................................................................................................ 66

7.3. Spatial resolution ............................................................................................................ 68

7.4. Thermal sensitivity ......................................................................................................... 71

7.5. Uncertainty Analysis ...................................................................................................... 73

8. Summary ............................................................................................................................... 75

9. REFERENCES ..................................................................................................................... 76

APPENDIX A ............................................................................................................................... 80

APPENDIX B .......................................................................................................................... 82

Index ............................................................................................................................................. 84

 
vi 

LIST OF FIGURES 

Figure 2—1. Predicted transmittance through a 12.7 cm (5 in) measurement path length 

for a simulated combustion atmosphere [9]. The soot, gases and wall 

temperatures are 600 oC. ....................................................................................... 14

Figure 2—2. Predicted radiation intensity through a 12.7 cm (5 in) path length for a 

simulated combustion atmosphere consisting of 0.6 ppm soot, 0.5 % CO, 

2.5 % CO2, and 97.0 % H2O [9]. The media temperature is held at 600 oC 

and the wall temperature varies from 0 oC to 600 oC. ........................................... 15

Figure 2—3. These three TIC are simultaneously viewing an identical thermal scene: a 

long corridor with a heated mannequin on the floor, and reflective and 

heated targets mounted on the wall at the end. A fire room is located 

adjacent to the corridor on the right. ..................................................................... 16

Figure 2—4.. Generic schematic of major TIC design components. ........................................... 18

Figure 2—5. Hybrid Pyroelectric BST Detector. This is a solid-state ceramic detector 

that spontaneously polarizes when exposed to thermal energy [4]. ...................... 18

Figure 2—6. Microbolometer. This is an array of individual sensors, each of which 

generates a small portion of the overall thermal scene. The sensor 

material is either vanadium oxide or amorphous silicon [11]. .............................. 18

Figure 3—1. Thermal imaging research needs, as indicated by participants of the 

Workshop on Thermal Imaging Needs for First Responders in December, 

2004. The key to the categories on the abscissa is provided in the 

following text. ....................................................................................................... 21

Figure 5—1. Plan view of Series 1 full-scale testing structure with inset showing the 

target and background. The target was placed on the floor in test 

configuration A and mounted on the wall 1.5 m from the floor in test 

configurations B, C, and D. .................................................................................. 29

Figure 5—2. TIC are positioned in the hot upper layer viewing a target through heavy 

toluene smoke, test configuration D (left), and in the lower layer viewing 

flames and high heat conditions, test configuration A (right). ............................. 30

Figure 5—3. Plan view of Series 2 full-scale fire test configuration with TIC viewing IR 

targets having at two distances. A heated mannequin in fire fighter 

turnout gear was also placed in the FOV. ............................................................. 31

Figure 5—4. The TIC were mounted on shelves which were repositioned midway 

through the tests (left). Two bar targets were used, one in the upper layer 

and one in the lower layer, along with a heated mannequin in fire fighter 

turnout gear, shown in infrared (right). ................................................................. 32

Figure 5—5. Visible image of typical hose stream test set up. Three TIC (behind foil on 

far left) are viewing a thermal target through a fog spray in the presence of 

a 2.2 MW heptane fire. ......................................................................................... 35
vii 

Figure 5—6. Comparison of heat effects, BST detector technology. These two TIC 

differ only in age, both having a 320 x 240 detector array. (where 

applicable uncertainties are determined statistically as stated in section 7.5 

and reported with a coverage factor of k=2) ......................................................... 38

Figure 5—7. Comparison of heat effects, VOx detector technology. ......................................... 39

Figure 5—8. Comparison of heat effects for ASi detector technology. ...................................... 40

Figure 5—9. Comparison of smoke effects for BST detector technology. ................................. 41

Figure 5—10. Comparison of smoke effects for VOx detector technology. ................................ 42

Figure 5—11. Comparison of smoke effects for ASi detector technology. ................................. 43

Figure 5—12. The relative FTIR signal measured at two times during an experiment 

burning carpet, padding, and wood. For comparison, measurement of the 

relative signal of a blackbody source at 200 °C (±5 °C, as per 

manufacturers documentation) is also shown. ...................................................... 44

Figure 5—13. Thermal images of a scene in which a fog spray is directed toward a wall 

in front of a 2.2 MW heptane fire. A BST-type TIC produced the center 

image and ASi-type TIC from different manufacturers produced the two 

other images. ......................................................................................................... 45

Figure 5—14. CTF of a thermal target viewed by three TIC through fog and straight (jet) 

sprays with a 2.2 MW fire in the field of view. The error bars represent 

the standard deviation of the CTF with a coverage factor of 2 (95 % 

confidence). ........................................................................................................... 46

Figure 5—15. Identical scene from full scale test series two observed with three different 

cameras. From top to bottom VOx, ASi, and BST TIC are utilized to view 

the same scene at the same time consisting of a mock victim on the floor 

with smoke and flames in the field of view. ......................................................... 48

Figure 6—1. Reflective test target used for image recognition tests. The test target 

dimensions are 61 cm (24 in.) in each direction. The white markings 

shown here are highly reflective foil with an ε ≤ 0.1 and the background is 

foam core with a black matte finish having an ε ≥ 0.9. ........................................ 51

Figure 6—2. An example viewing configuration is also shown (right) with the TIC 

positioned 1m away from the IRP target surface. ................................................. 51

Figure 6—3. Schematic diagram of image capturing setup. As the TIC views a thermal 

target, a high resolution visible camera is focused on the TIC display. A 

mounting bracket (not shown) is to be provided by the TIC manufacturer 

to optimally position the visible camera. .............................................................. 52

Figure 6—4. Test target setup used for the contrast and effective temperature range tests. 

For large area contrast, the bars in the middle of the test target are ignored. 

The standard deviation of the combined pixel intensities within the dashed 

areas on the left and right side of the test target are calculated, then 

divided by the Bitdepth to determine the contrast as a function of T2, 

which changes from 25 °C to Tmax. ....................................................................... 55
viii 

Figure 6—5. Alternative test setup for contrast and effective temperature range. When 

space is an issue mirrors may be used to redirect the thermal radiation to 

the TIC. The results presented in this paper were obtained in this 

configuration. ........................................................................................................ 55

Figure 6—6. This test target is used for the contrast and effective temperature range 

tests. For the effective temperature range, the contrast of the central area, 

which incorporates bars having a constant temperature difference, is 

measured while the hot blackbody surface temperature (T2) increases. ............... 56

Figure 6—7. Test setup for measuring the nonuniformity of a TIC. The TIC is placed 

close to the surface (~5cm) of a uniform large area blackbody surface. The 

temperature is is increased and the images are taken by the visible camera 

to determine image nonuniformity. ....................................................................... 57

Figure 6—8. Variation in nonuniformity of a TIC with increasing temperature. As the 

test target temperature increased, nonuniformities became more 

apparent. The TIC shifted to a less thermally sensitive mode between the 

100 °C and 200 °C images. ................................................................................... 58

Figure 6—9 Slanted edge spatial resolution test target. The slant is 5 o from vertical, the 

hot and surrounding temperatures are held constant throughout the test. 

The target dimensions are at least 15 cm in each direction. All surfaces in 

the field of view have ε ≥ 0.94 ±0.002.................................................................. 60

Figure 6—10 Sample spatial resolution data. The spatial resolution is obtained by 

integrating between the MTF (red line) and the nonuniformity (blue line). ......... 61

Figure 6—11. Experimental setup for thermal sensitivity test. The two blackbodies are 

adjusted until they both have the same luminance on the TIC display. 

Then one blackbody temperature is slowly decreased until a 2 % 

difference in luminance is observed between the two blackbodies. ..................... 62

Figure 7—1. Plots of large area contrast and bar contrast data used to determine image 

contrast and effective temperature range of a TIC using an ASi, 120 x 160 

detector array. Test results for two tests are shown. ............................................ 64

Figure 7—2. Plots of large area contrast and bar contrast data used to determine image 

contrast and effective temperature range of a TIC using an BST, 240 x 320 

detector array. Test results for two tests are shown. ............................................ 65

Figure 7—3. Plots of large area contrast and bar contrast data used to determine image 

contrast and effective temperature range of a TIC using an VOx, 120 x 

160 detector array. Test results for two tests are shown. ..................................... 65

Figure 7—4. Actual nonuniformities observed from three different TIC at a variety of 

temperatures. BST, VOx, and ASi detector technologies are all represented 

along with a variety of different nonuniformities present in these cameras. ........ 67

Figure 7—5. Image nonuniformity as a function of target temperature while looking at a 

uniform temperature surface. For the three specific TIC tested, the VOx

TIC produced the least nonuniformity while the ASi and BST cameras had 

higher nonuniformities at different temperatures. ................................................ 67
ix 

Figure 7—6. Illustration of how of how three different cameras interpret the same ‘knife 

edge’ thermal target. The three different cameras have different sensor 

technology, but also have different pixel resolutions (320x240, 160x120, 

and 160x120 respectively), optics, and internal image processing that 

affects the spatial resolution of the image on the display. The analysis of 

these images is presented in Figure 7-6. ............................................................... 69

Figure 7—7. Comparison of the spatial resolution of the BST, VOx, and ASi TIC. The 

SFR value given for each camera technology represents the area between 

the MTF curve and Nonuniformity. The spatial resolution measurement 

for each camera is dependent upon the nonuniformity measurement as 

well. ....................................................................................................................... 70

Figure 7—8. Illustration of the temperature independence of the spatial resolution 

measurement. The temperatures are indicated in Celsius. Once the original 

values (top) are normalized (bottom) the effect of image contrast 

(temperature difference) can be eliminated. The line for 40 °C on the right 

does not follow the other trends because there needs to be a minimum 

contrast in the knife edge image. .......................................................................... 71

Figure 7—9. Example thermal sensitvity response for a characteristic TIC. A smaller 

value for thermal sensitivity indicates that the camera is more sensitive to 

small differences in temperature. The thermal sensitivity increases with 

increasing nominal temperature due to a larger contrast necessary for the 

user to percieve a temperature difference. ............................................................ 72

 
x 

LIST OF TABLES 

Table 4-1. Thermal Classes (Donnely et al.) ................................................................................ 23

Table 4-2. Peak conditions measured during typical compartment fire experiments ................... 25

Table 4-3. First Responder TIC Operations .................................................................................. 26

Table 5-1. Series 1 test configurations ......................................................................................... 28

Table 5-2. Series 2 test configuration. .......................................................................................... 33

Table 5-3. Thermal environment (where applicable uncertainties are determined as stated 

in section 7.5 and expressed with a coverage factor of k=2). ............................... 36

Table 5-4. Proposed TIC Testing Conditions. .............................................................................. 49

Table 7-1: Uncertainty in full scale experimental test data. ......................................................... 74

Table 7-2: Uncertainty in bench scale experimental data. ............................................................ 74
11

1. INTRODUCTION 

Infrared (IR) technology for firefighting applications has matured to the point that most first 

responder organizations either have purchased or are considering the purchase of thermal 

imaging cameras (TIC1). TIC can provide first responders with critical information to size up a 

fire incident, track fire growth, and to locate victims, other first responders, and egress routes. 

While these devices represent a significant investment, typically on the order of $10,000 per 

camera, first responders have little guidance on instrument performance beyond manufacturer 

literature and recommendations from other users [1]. These issues are further complicated 

because the demands placed on TIC are application dependent. The end users may have very 

different ideas about which imaging properties are most important: sharp image contrast may be 

sufficient for some fire fighting applications, such as finding the source of a fire, but high 

thermal sensitivity may be required to locate a person or structural component when flames and 

water are in the imager’s field of view (FOV). Currently, there are no standardized performance 

guidelines available to aid end users in making purchasing decisions. 

Over the past several years, the Fire Research Division at the National Institute of Standards and 

Technology (NIST) has been conducting research on TIC imaging performance metrics and test 

methods with the overall objective of providing science-based information to national standards 

developing organizations (SDO). The National Fire Protection Association (NFPA) is currently 

developing a standard on first responder thermal imaging cameras, Proposed NFPA 1801 

Standard on Thermal Imagers for the Fire Service [2], and ASTM International is revising a test 

method on infrared detector sensitivity, ASTM E1543-00 Standard Test Method for Noise 

Equivalent Temperature Difference of Thermal Imaging Systems [3]. Both of these organizations 

are taking this work into consideration as they move through their standards developing 

processes. 

The SDOs mentioned above operate through committees, which draft a document based on input 

from users, manufacturers, technical experts, and the public. The committees make decisions 

regarding the content of the standard on a consensus basis. Before the final form of the standard 

document is published, draft versions of the document are offered to the public for proposed 

changes in scope and for revisions to text. As an unbiased, non-commercial entity with 

experience in fire research and testing of first responder personal protective equipment, the 

Building and Fire Research Laboratory (BFRL) at NIST is well positioned to assist in the 

formation of a standard for TIC. At the discretion of the committee, all or part of the 

recommendations provided to the SDO, including the recommendations resulting from this 

project, may or may not be included in the final standard documents. 

 

1

 The acronym TIC shall be used throughout this text in reference to both the singular and plural 

forms, i.e., Thermal Imaging Camera(s), as befits the context of the sentence in which it is used. 
12

1.1. Approach 

This work began with an assessment of the thermal imaging needs and activities of first 

responders. To gather this information, a workshop on Thermal Imaging Research Needs for 

First Responders was held at NIST in December, 2004 [4]. Ties were established between 

industry, the first responder community, and NIST that have, over time, helped shape the 

Proposed NFPA 1801 draft standard and have also accelerated the somewhat protracted standard 

development process. The results of the workshop will be discussed in Section 3. 

Existing standards were collected and reviewed to ensure that the recommended testing 

conditions in this work are consistent with standards on other first responder equipment that is 

exposed to similar operating conditions, as well as standards and test protocols on infrared 

cameras that are used in other applications, when appropriate [3, 5, 6]. A survey of the literature 

was also performed to explore existing work in which the fire environment was well 

characterized and pertinent to TIC testing [7]. This work is explained further in Section 4. 

Several series of full-scale tests were conducted at NIST’s Large Fire Laboratory, in which 

attention was focused on temperature extremes and the presence of obscuring media such as 

smoke. These tests, outlined in section 5.5, helped bracket the thermal conditions in which TIC 

are used and also provided design guidance for bench-scale experiments. Bench-scale test 

facilities were constructed with an emphasis on developing test methods that can be replicated in 

testing laboratories that would be engaged in certifying TIC products under the provisions of a 

national standard. Detailed discussion of the full- and bench-scale tests conducted at NIST to 

support TIC research are presented in section 6. 

The consolidation of all of this information, e.g., first responder feedback, literature search, and 

full- and bench-scale testing, provided a basis for defining testing conditions that challenge TIC 

in meaningful ways. Given a set of expected tasks that would potentially be performed by first 

responders using TIC in each of these testing conditions, which have been categorized into 

“thermal classes”, it is possible to relate performance metrics directly to the environment in 

which TIC are used and the tasks typically performed by first responders in each thermal class. 

This is the subject of Section 5. 

Performance metrics that describe TIC image performance are discussed in Section 6. These 

metrics include: contrast, which measures how well the TIC can represent differences in 

temperature; effective temperature range, which measures the maximum temperature at which 

the TIC is able to produce an image; spatial resolution, which measures how will the camera can 

discern small details; nonuniformity, which measures the quantity of noise present in the thermal 

image produced by the TIC; and thermal sensitivity, which measures the smallest temperature 

difference that the TIC is able to differentiate. Recommended bench scale experimental setups 

and test methods used to make these measurements are also presented. 

The TIC display screen is the normal user interface and as such must be included as part of the 

system in imaging performance standards. The user’s perception of the image displayed is also 

important because his/her ability to perform a task, such as finding a hazard, depends on how 

well he/she can interpret the image displayed on the TIC screen. 

 
13

2. BACKGROUND 

Before delving deeply into the performance metrics and testing procedures presented in this 

report, it is instructive to begin with some background on thermal imaging. The following 

subsections are intended to explain how TIC operate for fire service applications. It should be 

noted that thermal imagers and infrared technology in general are used for many purposes, 

including industrial processing, military, scientific, and building inspection applications. While 

there are many commonalities between the applications, there are also many differences. 

2.1. Imager design 

The nature of the conditions under which TIC are used has in large part influenced the 

development of imaging technology for fire service applications. For example, a fire fighter may 

encounter high temperatures, open flames, pools and sprays of water, and thick smoke; therefore 

it is important that TIC are capable of seeing in these obstructive conditions with a minimum 

amount of interference from the surrounding environment. Fire service thermal imagers are 

generally designed to detect radiant thermal energy in the 8 μm – 14 μm spectral range. This 

energy is radiated from solid surfaces and from certain gases that radiate. 

A characteristic of the radiating surfaces and gases called emissivity affects how the thermal 

radiation intensity relates to the actual temperature in a way that can make the surface or gas 

appear to have a temperature that is different from reality [8]. A surface or gas having an 

emissivity of 1 is said to be a “blackbody”, meaning that it absorbs and re-emits all energy 

incident upon it, and thus is representative of its actual temperature. A surface or gas having an 

emissivity of 0 reflects all energy, making the surface or gas appear colder than it actually is. In 

general, surfaces that are flat black in color and somewhat rough in texture tend to have high 

emissivities and surfaces that are shiny and smooth tend to have low emissivities. Most TIC are 

designed to use a constant emissivity value of 0.95 in their internal algorithms used to convert 

the radiant energy signal to a temperature value. The further away an object’s emissivity is from 

0.95, the less accurate that object’s surface temperature will appear to be. The term “apparent 

temperature” is used to account for temperature deviations caused by differences in emissivity. 

Transmittance is a normalized measure of the clarity of a view path, or how much radiant energy 

is ‘transmitted’ through something, with 0 being completely opaque and 1 being perfectly clear 

(like looking through clean glass in the visible spectrum). The visible spectrum is between the 

wavelengths of 0.4 μm and 0.7 μm, the infrared spectrum is anything above 0.7 μm in 

wavelength. Figure 2—1 presents the transmittance of various gasses and soot which are likely 

to be present in a fire situation. Note that even though CO, CO2, and water vapor are not visible 

to us in the visible spectrum, in parts of the infrared spectrum they block out significant 

quantities of the infrared radiation. A high transmittance band approximately in the 8 μm – 14 

μm spectral range is evident, for this reason the fire fighting TIC are designed to operate in this 

region of the infrared spectrum. 

Radiant intensity (the quantity of radiation emitted by an object) as a function of wavelength is 

shown in Figure 2—2. Thermal radiation coming from hot surfaces and flames may interfere 

with TIC imaging performance by creating too much signal. The peak in radiant intensity is well 

below the spectral range of interest, although it may still interfere with the imager’s ability to see 
14

Figure 2—1. Predicted transmittance through a 12.7 cm (5 in) measurement path length for a 

simulated combustion atmosphere [9]. The soot, gases and wall temperatures are 600 oC. 

the target in some test conditions. In some cases the TIC may also be able to recognize radiation 

emitted from the camera its self, this narcissus is largely avoided by optics design which 

collimates the infrared radiation, keeping it in a straight line so that only energy from the scene is 

interpreted by the camera. 

The software program RADCAL [9] was used to perform these transmittance and radiant 

intensity simulations. The soot concentration of 0.6 ppm is a typical value derived from fullscale testing results (Section 5); however, the water vapor value of 97.0 % is based on the 

maximum water concentration attainable in superheated conditions (above 100 oC at 101.325 

kPa). The actual water vapor concentration is expected to be much less than this. Therefore 

smoke is likely to be the principal absorber in the cell, and thus an important experimental 

parameter. 

Fire fighters may rely in part on a TIC to navigate their way through a burning structure; 

therefore most imagers employ a wide field of view (FOV) in the range of 40o to 60o. There are 

few cases in which a fire fighter would need to focus on an object less than 1 m away, which 

encourages the use of relatively robust and lower cost fixed focal length optics that focus from 

1 m to infinity. While temperature measurements provide useful information in a fire situation, 

the accuracy of the measurement is not as critical as it might be in other thermal imaging 

applications. 
15

Figure 2—2. Predicted radiation intensity through a 12.7 cm (5 in) path length for a simulated 

combustion atmosphere consisting of 0.6 ppm soot, 0.5 % CO, 2.5 % CO2, and 97.0 % H2O [9]. 

The media temperature is held at 600 oC and the wall temperature varies from 0 oC to 600 oC.

The urgency of a fire event also dictates the need to keep the operation of the imager as simple as 

possible. Most TIC feature fully automated gain, focus, and iris settings, generally offering few 

manual controls other than a large on/off button that can easily be accessed by a fire fighter 

wearing heavy gloves. In some cases the imager may have one or two added functions, such as a 

zoom button or a toggle between IR and visible viewing. 

2.2. Detector technologies 

There are currently three well-established detector/sensor technologies available for purchase: 

barium-strontium-titanate (BST), vanadium oxide (VOx), and amorphous silicon (ASi). 

Manufacturers may utilize a single detector technology or may choose to offer a selection of TIC 

models possessing different technologies. Most detectors used for first responder applications 

are uncooled focal plane arrays (FPA), utilizing an array of sensors located at the focal plane of 

the optics, each specific detector technology is capable of generating different levels of 

information in the displayed image. Both the VOx and ASi cameras utilized uncooled FPAs 

while they BST cameras have a small thermoelectric cooler to stabilize the detector temperature. 

VOx and ASi cameras are called microbolometers, which means that the detector pixels are 

essentially very small heat flux gauges, changing their electrical resistance based on how much 

heat is absorbed by the pixel. The strengths and weaknesses of each detector technology are 

evident in Figure 2—3, where TIC representing the three different detector types are viewing an 

identical thermal scene simultaneously. The differences seen in this figure are the result of not 

only different detector technologies, but also different optical and electronic systems, which can 

contribute significantly to overall image quality. These three TIC also are of different sizes, 

weights, and cost. 

 
16

Figure 2—3. These three TIC are simultaneously viewing an identical thermal scene: a long 

corridor with a heated mannequin on the floor, and reflective and heated targets mounted on the 

wall at the end. A fire room is located adjacent to the corridor on the right. 

VOx 

ASi 

BST 
17

The signal from the FPA is relayed to the imager’s signal processor via a charge-coupled device 

(CCD). The optics package provides an interface between the signal processor and the recorded 

image and makes an important contribution to the overall performance of the instrument. This 

fact should be considered when viewing Figure 2—3. There are as many ways of designing 

optic and electronics packages as there are imager form factors and target market prices. The 

major design components of a generic TIC are shown below in 

Figure 2—4. 

The thermal energy that radiates onto the TIC lens is focused on the detector. The signals 

generated by the detector are then manipulated into a video signal that is sent to the display. 

Some TIC also have a video output that can be used to record the signal via a hardwired 

connection or wireless transmitter/receiver . The signal that goes to the video output is not 

usually exactly the same as the signal that goes to the TIC display. The overall usefulness of the 

TIC is therefore very much dependent on the ability of the observer to interpret the image 

displayed on the screen well enough to perform a task or operation successfully. 

The two typical FPA sensor sizes are 240 rows x 320 columns and 120 rows x 160 columns. The 

BST detectors, shown in Figure 2—5, are solid-state ceramic devices with an embedded array of 

sensors (or nodes) that convert changes in electrical polarization to voltage differences. A 

thermoelectric cooler provides thermal stability. These are AC-coupled detectors that measure 

relative levels of infrared radiation, thus the detector output requires a correction based on 

reference points provided by a chopper. A chopper is a bladed wheel that rotates directly in front 

of the detector such that it sees the chopper blades alternately with the thermal scene. The 

chopper blades are assumed to have a constant temperature2

 and the detector nodes are 

continuously reset to a uniform value corresponding to that temperature every time a chopper 

blade passes in front of the detector array. The oscillation between the thermal scene and the 

chopper blades provide the AC component to the detector signal. 

The VOx and ASi detectors, see Figure 2—6, are both microbolometer devices that measure 

changes in the electrical resistance of the sensor material due to heat from infrared radiation. 

Microbolometers don’t require cooling but are relatively sensitive to detector temperature. The 

output from these DC-coupled detectors is a function of the absolute level of incident infrared 

radiation. A shutter is used to periodically reset the detector’s absolute radiation input level and 

prevent drift among the detector pixels [10]. Initially VOx was used as the sensor material, 

however, ASi is now also emerging as a viable sensor material. 

Other detector technologies that have not become commercially available yet are under 

development as well. The performance metrics and test methods proposed with this work are 

intended to treat TIC as a “black box” from the lens to the displayed image, and therefore are 

expected to accommodate new technology as it becomes practicable. 

 

2

 There is very little variation in the uniformity of the chopper blade temperature since the 

chopper is completely enclosed within the camera and only views the ‘hot’ scene for a small 

fraction of each revolution (<10%) 
18

Target & 

Background Amplifiers Signal Processing

Optical 

System Detector

Display

Observer

Temperature difference, 

emissivity, radiant energy, 

target size, obscuring media Infrared system

Volts, frequency, amplitude, 

monitor clarity, observer 

response

Video 

Signal

Input Output

Figure 2—4.. Generic schematic of major TIC design components.

Figure 2—5. Hybrid Pyroelectric BST Detector. This is a solid-state ceramic detector that 

spontaneously polarizes when exposed to thermal energy [4]. 

Figure 2—6. Microbolometer. This is an array of individual sensors, each of which generates a 

small portion of the overall thermal scene. The sensor material is either vanadium oxide or 

amorphous silicon [11]. 

 Resonant

IR Absorber

Thermal

Isolation

Mesa

Readout IC

Metal

Contacts

BST Pixel
19

2.3. Operating environment 

An important step in the process of developing a meaningful performance standard for TIC is to 

establish test conditions that adequately represent the range of environments in which these 

cameras are used. First responders may use TIC for field operations ranging from searching for 

a hidden fire source, to directing a hose stream, to detecting the location of hazardous materials. 

New uses for TIC are being discovered as they become more widely used in the first responder 

community. At one boundary of the range of conditions in which the imaging performance of 

TIC is challenged, open flames and water coated surfaces may be seen in the same FOV. At the 

other boundary, the ability to see very slight differences in temperature and/or emissivity may be 

required to discern the level of contents of a chemical drum at near ambient temperature or in 

cases when a cold basement or warehouse is being searched. While it is relatively simple to 

capture the essence of the latter test condition in a repeatable laboratory setting, the former 

scenario, along with other conditions related to fire fighting, can be much more challenging and 

therefore are given particular attention in this work. 

Decades of fire testing have shown that the gas temperature in a naturally ventilated burning 

room stratifies, due to buoyancy, into a upper layer that contains hot combustion by products and 

a cooler lower layer composed mainly of ambient air [12, 13]. The time-varying severity of the 

conditions in the room of fire origin and adjacent or nearby rooms will change depending on the 

type and amount of materials burning, the thermal properties of the room surfaces, the ventilation 

conditions, the size of the room, and a number of other factors. As most fire fighters will attest 

or describe, no two fires are exactly the same. For this reason, incorporating the chaotic and 

dynamic nature of fire conditions into readily controlled, reproducible, and repeatable tests that 

will be performed by numerous parties is a difficult task. 

There are two basic ways in which operating conditions affect TIC: first, the camera itself must 

be rugged enough to function in elevated temperatures and humidity, and other adverse 

conditions; and second, the camera must be capable of producing images that provide useful 

information to the user. Performance metrics and standard testing protocols address the ability 

of the TIC to operate in a harsh environment. In 1999 a U. S. Navy report describes a series of 

tests conducted to determine which of eight commercially available TIC were sturdy enough to 

function in the harsh environment of a fire onboard a ship [14]. The Navy utilized 27 criteria 

ranging from battery life to corrosion resistance by which to judge the performance of the 

imagers. Image quality tests address the ability of the TIC to capture an infrared scene with 

sufficient sensitivity and detail to enable the user to perform a particular activity, such as 

searching for a fire victim. The work done to date at NIST on this project is primarily directed 

toward the evaluation of the imaging performance of TIC, although some related work is also 

concerned with certain aspects of the physical robustness of TIC. 

2.4. Performance metrics 

There are many generally accepted performance metrics designed to evaluate TIC used in 

scientific, security, and industrial applications [15]. A brief list of relevant standards is included 

in Appendix A of this document. A comprehensive discussion of these metrics and their 

implementation is provided by Holst [16]. This is a natural place to begin the development of 

performance metrics for fire service applications, however there are important differences 
20

between scientific and fire fighting thermal imagers that affect the way image quality can be 

measured. As discussed in Section 2.1, TIC used by fire fighters tend to have fully automated 

controls, relatively large FOVs, and long minimum focusing distances. These characteristics 

make some of the established performance metrics difficult or impossible to apply. The NIST 

evaluation facilities were developed to determine which of the existing performance metrics are 

feasible to use for this application, to explore possible modifications that may improve their 

function, and to propose new imaging performance metrics when needed. 

Another important consideration is that the end users of these imagers would be better served by 

performance metrics that are presented in a meaningful context. For example, evaluations 

involving individual pixels would probably be lost on a fire fighter. Performance metrics that are 

tied to understandable physical properties of the image and/or test conditions impart additional 

significance to fire fighters and other first responders, and thus will facilitate their acceptance 

into practical use. 

The objective of this work is not to establish a rating system for all TIC used in first responder 

applications, rather, it is to provide imaging performance measurements that describe the 

usefulness of TIC in meaningful operating conditions. This approach leaves the operators free to 

decide which TIC perform adequately while also considering other criteria such as size, weight, 

anticipated uses, and cost. 
21

3. WORKSHOP ON THERMAL IMAGING RESEARCH NEEDS FOR FIRST 

RESPONDERS 

The Workshop on Thermal Imaging Research Needs for First Responders [4] was held at NIST 

in December of 2004 in order to better understand the needs of users, manufacturers, government 

agencies, and other proponents of TIC technology and to identify barriers that impede advances 

in the application of thermal imaging technology to emergency response. This workshop 

provided a forum to discuss the strategies, technologies, procedures, best practices, research, and 

development that can significantly improve thermal imaging technology for the first responder 

community. After hearing presentations, the workshop divided into three breakout sessions to 

discuss and prioritize issues relating to the following four questions. 

1. What technological advances are needed? 

2. What are the research needs for first responders? 

3. What performance metrics are needed and how do they differ from current methods? 

4. What standards are needed? 

The issues that were found to be most important to the attendees of the workshop, divided into 

industry and first responder results are shown in Figure 3—1. The workshop proceedings are 

available at http://fire.nist.gov/bfrlpubs/fire05/PDF/f05036.pdf. 

Figure 3—1. Thermal imaging research needs, as indicated by participants of the Workshop on 

Thermal Imaging Needs for First Responders in December, 2004. The key to the categories on 

the abscissa is provided in the following text. 

1 2 3 4 5 6 7 8 9 10

Industry

First Responders

Relative Priority
22

Key for item numbers in abscissa of Figure 3-1: 

1. Image quality (research, metrics, standards, contrast, sensitivity) 

2. Durability (metric, mean time between failures, standard test methods for ruggedness) 

3. Training and certification for users 

4. Establish minimum/typical test environments 

5. Human factor/ergonomic and human dynamics research 

6. Image display (technology, viewability, metrics) 

7. Battery and charger (life/maintenance, icons, and self-test improvements) 

8. Reduction in imager cost (“water bottle” sized package priced at $2K) 

9. Standard target (for field test/calibration and emissivity target for turnout gear) 

10. Imager self-test procedure and warning system 

One important result of the workshop was the formation of a follow-on group of TIC 

manufacturers and fire service personnel that began meeting to devise an approach for 

standardizing the TIC user interface. This group grew to include representatives from all the 

U.S. manufacturers of TIC and TIC detectors. Eventually the image quality work described 

herein was included with the user interface results of the follow-on group. 

In addition to hearing directly from stakeholders about their TIC research needs, information 

about fire environments and other operating conditions was also collected from the literature, 

from existing standards for other personal protective equipment, from internal test reports, and 

from full-scale and bench-scale testing. In order to gain firsthand experience on the use of TIC 

in burning buildings, some NIST personnel underwent training through a professional TIC 

training course3

 for first responders. Direct communication between first responders and NIST 

personnel regarding the use of TIC and the environment in which they are used has continued 

throughout this research effort. 

 

 

3

 See SAFE-IR, http://www.safe-ir.com/ 
23

4. SURVEY OF RELEVANT STANDARDS AND WORK BY OTHERS 

In this section, existing standards that relate to the development of a TIC performance standard 

are discussed. Additionally, existing research is presented that reports information on the 

thermal environment in which TIC may be used. 

4.1. Relevant standards 

There are several standards developing organizations that produce standards on electronic and 

other personal protective equipment used by first responders, and standard test methods do exist 

for TIC used in non-emergency service applications, but at the time of this writing there is no 

completed standard specifically written for TIC used by the fire service. 

The following is a brief discussion of some details of existing standards that may have bearing 

on TIC operating conditions for design robustness and image quality tests. A list of these 

standards is provided in Table B-1 of Appendix B. American National Standards Institute 

(ANSI) standard ANSI/ISA-12.1201 covers intrinsic safety testing for nonincendive devices 

[17]. Several ASTM International standards are functional tests for exposure to salt spray [18], 

transmittance of lens [19], flame resistance [20], and liquid penetration [21]. There are also 

several ASTM test methods for infrared camera image quality [3, 5, 6, 22-24]; however, these 

test methods do not include extreme operating environments in their tests. Pertinent publications 

from the International Standards Organization (ISO) include enclosure integrity [25], 

electromagnetic compatibility [26], functional safety [27], and resolution measurements for still 

cameras [28]. The Military Standard, MIL-STD 810F, tests resistance to mechanical 

acceleration [29]. Underwriters Laboratory (UL) produces a large number of standard test 

methods for many aspects of design for electrical and electronic devices, such as proper 

grounding and wiring for switches and terminal blocks. The Video Electronics Standards 

Association (VESA) writes standard test methods for measuring display performance [30]. In 

addition to the above standards, which are not specifically written for fire service equipment, 

NFPA produces standards on communications systems [31], protective clothing for structural 

firefighting [32], protective clothing for wildland firefighting [33], self-contained breathing 

apparatus [34], and personal alert safety systems [35], which are intended for equipment that 

might be exposed to thermal environments similar to those experienced by TIC. Note that there 

are only two NFPA standards, on self-contained breathing apparatus [34, 36] and on personal 

alert safety systems [35], which are written specifically for electronic devices used in burning 

structures. Fire fighters sometimes use electronic gas detectors, but these devices have no formal 

standards for operation or functionality, although some comply with the ANSI/ISA standard on 

nonincendive devices [17]. Currently, some TIC manufacturers voluntarily adhere to some of 

the standards discussed here, but are not required to do so. 

Table 4-1. Thermal Classes (Donnely et al.)

Thermal Class Maximum Time (min) Maximum 

Temperature (°C) 

Maximum Heat Flux 

(kW/m2

) 

I 25 100 1 

II 15 160 2 

III 5 260 10 

IV <1 >260 >10 
24

4.2. Work by others 

Recent work by Donnelly et al. [7] recommends the concept of thermal classifications to 

systematize design robustness tests on first responder electronic equipment. The 

recommendations are based on experiments or studies performed by several research groups. 

The thermal classes are reproduced in Table 4-1.

The thermal classification system is useful for representing the increased risk to fire fighters 

related to the thermal environment. The most prevalent use of TIC would be in the first three 

thermal classes. Systematic use of a TIC in response to the fourth class of fires is unlikely as not 

enough time would be available under such hazardous conditions, however, brief exposure may 

occur as a fire fighter retreats from impending severe conditions. In addition, the current 

generation of TIC detectors tend to become saturated under such conditions, negatively 

impacting their effectiveness. It is expected that trends in visibility conditions scale with thermal 

class. For example, it is expected that less smoke is associated with a smaller Class I fire 

situation than a larger Class II or Class III fire. 

It is useful to consider the results from compartment fire experiments to better understand the 

range of visibility and imaging conditions which a fire fighter may encounter. To evaluate the 

performance of TIC, the smoke concentration and possibly some gas species must be considered. 

Unfortunately, the understanding of smoke generation from a fire is incomplete. In a 

compartment fire burning realistic materials, the smoke generation rate (smoke yield per unit of 

fuel mass) is difficult to predict to within a factor of six or more, even for relatively simple fuels 

[37]. The smoke produced will increase with the fuel mass burning rate and the fire heat release 

rate, so, generally, the smoke concentration can be expected to increase with the thermal class 

categories listed in Table 4-1 as a fire grows and spreads and a hot upper layer develops. 

A typical situation in which a TIC is used may involve a residential or commercial fire, where 

furnishings, structural materials, electrical appliances, and other materials burn in a flaming or 

smoldering mode. Many common commodities are composed of either cellulosic or 

thermoplastic materials. As these commodities burn, smoke and combustion byproducts such as 

carbon dioxide (CO2) and water (H2O) will be produced in significant quantities. Although much 

fuel mass is converted to CO2 and H2O, a significant percentage can also go to the production of 

smoke, varying from about 1 % to 20 % by mass, depending on the fuel type [38]. Smoke, or 

soot, is a product of incomplete combustion and is not a gas, but a complex solid particulate 

whose form and mass concentration depend on the type of fuel and the ventilation conditions 

within the compartment. Once formed, it is transported with other combustion products, first 

within a compartment and then beyond the room of origin. In actual fires, trace combustion 

species that are optically active (e.g., HCN, C2H4, C2H6) may also be formed [39, 40]. These 

species are relevant to TIC performance because they may be optically active in the 8 μm to 14 

μm portion of the infrared spectrum which is employed by TIC. In practice, these species may 

(or may not) negatively impact a TIC in realistic applications, as the combination of 

concentration and band intensities may (or may not) be significant. 

Several full-scale compartment fire experiments in the scientific literature provide information 

on conditions in enclosure fires, such as those that may be encountered during fire fighting 
25

operations. This information is also relevant when considering the performance of TIC. Table 

4-2 summarizes some of these results, listing the fire heat release rate (Q& ), the peak upper layer 

gas temperature, and the peak concentration of smoke in the room of fire origin. In the 

experiments listed in the table, the fire was ignited and a hot upper layer developed as noted by 

increasing values of temperature and smoke density. If the fires were controlled or prescribed, 

quasi-steady state conditions may have occurred in the upper layer, provided that the fires burned 

for a sufficiently long duration. Empirical correlations have been derived that relate the hot gas 

layer temperature and species to the heat release rate. As a fire spreads and grows through an 

enclosure or building, the hot upper layer in a severe fire can reach temperatures and smoke 

concentrations as high as 1000 °C and 20 g/m3

, respectively. In a fire that is not prescribed (nonsteady), the heat release rate depends on naturally occurring fire spread and growth. In that case, 

the time rate of change of the room conditions will depend on the fire heat release rate, the fuel 

type, the ventilation, the room size, and a number of other parameters. 

Table 4-2. Peak conditions measured during typical compartment fire experiments 

Reference Therma

l Class 

Heat Release 

Rate Q& (kW) Fuel Type 

Peak 

Temperature 

(°C) 

Peak Smoke 

Density 

(g/m3

) 

Ref. [41] IV 1,000 (Peak) furnishings 1100 1 4

Ref. [42] III 200 (Peak) furnishings nr 3 20 

Ref. [43] IV 

3,000 heptane/toluene 1

 540 2 

IV heptane 500 0.3 

Ref. [44] III 1,000 toluene 200 0.4 

Ref. [45] IV 100 natural gas 

/acetylene 2 660 nr 

Ref. [13] IV 600 natural gas/wood 5 950 nr 

1. liquid mixture of 60 % Heptane and 40 % Toluene (by mass). 

2. gaseous mixture of 76 % natural gas and 24 % acetylene (by mass). 

3. nr: not reported. 

4. an opticsal density (D/l) of 5 m-1 was reported. The value of D/l is related to the smoke density 

(Cs) and the specific extinction coefficient of smoke (ξ) by Cs = (D/l)/ξ, where ξ is typically on 

the order of 5 m2

/g [42]. 

5. natural gas burner below wood-lined ceiling. 

 
26

4.3. TIC operations 

Before operating conditions are discussed, it is instructive to list the ways that TIC are currently 

being used in the field. This information is provided in the table below. From this, one can 

estimate the thermal and spectral environments that impact the design robustness and imaging 

performance of the cameras. Table 4-3 is not a comprehensive list; it was compiled from input 

from a variety of users and is expanding as the first responder community increasingly accepts 

TIC technology. 

Clearly, not all first responders use TIC for every activity listed. Each first responder 

organization has its own set of thermal imaging needs and would potentially benefit from 

knowing how well a TIC performs in the activities that are most important to it. Due to tradeoffs in the design of a TIC, it is unlikely that a single TIC will perform “better” than all of its 

competitors in every one of these activities. For example, TIC “A” might be optimized such that 

it can discern intermediate temperatures (such as a human) relatively well when flames are in the 

FOV, but it may not provide adequate thermal sensitivity at ambient temperatures to determine 

chemical levels in containers. On the other hand, TIC “B” may not produce sharply defined 

images in any of the above listed situations but can produce adequate images to perform the tasks 

needed. The needs of the first responders are best served when they are confident that the TIC 

will not fail in adverse conditions, and the image produced by the TIC is of a sufficient quality 

for their particular suite of activities. 

Table 4-3. First Responder TIC Operations 

Activity Description 

Size up Assess hazard, find fire/heat sources, escape points, and vents 

Communication Lead or direct searches, interface with incident command, account for team 

members 

Search Locate victims, other first responders, fugitives, missing persons in dark and/or 

smoky environments 

Tactical 

Direct hose stream, check upper layer temperature, check for changing 

conditions, detect obstacles, passageways, damaged structural members, judge 

distances, use in rapid intervention teams 

Overhaul Ensure fire is out, look for hidden smoldering and hot spots 

Forensics Identify source of fire, determine fire spread, record video during fire for later 

use as evidence 

Wildland Fires Ground and air based search for hot spots and personnel 

Hazmat Determine material levels inside containers, track material movement and spill 

spread limits 

Other Preventative building maintenance, emergency medical applications, motor 

vehicle accident investigations 
27

5. INFORMATION CONSOLIDATION- TEST CONDITIONS 

As discussed in the previous section, when using a TIC inside a burning building, a fire fighter 

may encounter high temperatures, open flames, water sprays, dust, and thick smoke. To augment 

the literature search and to gain firsthand knowledge of TIC imaging performance in structure 

fires, two series of full-scale tests were conducted wherein the range of operating conditions 

expected in real structure fires was explored. The objectives of these tests were to characterize 

the image quality of the TIC and the way it relates to full-scale thermal environments, and to 

establish boundaries for gas, smoke, and surface temperatures and concentrations to be used in 

bench-scale tests. Also, these tests contributed to the adoption of a classification system for 

thermal conditions, which will be discussed in more detail in Section 7. In these tests, a 

collection of first responder TIC, scientific TIC, and visible cameras were trained on infrared 

targets, which were placed either in or adjacent to the room of fire origin. Temperature, gas, and 

smoke measurements were made both within the room of fire origin and in the adjacent spaces. 

The TIC and the targets were located at various times within the hot, smoke laden upper layer 

and within the cooler lower layer. Each of the experimental setups will be described in the 

following two subsections; the results for both test series will be discussed together as a whole in 

subsection 5.5. An important set of measurements of the constituents of smoke was part of one 

of the full-scale test series, which warrants special discussion. These measurements, and the 

results, are presented in subsection 5.3. 

5.1. Series 1 test facility 

This initial series of full-scale fire tests was designed to provide quantitative information on the 

thermal environment resulting from different types of structure fires. Qualitative information 

regarding TIC imaging performance in these conditions was also collected. This information 

was used to design bench-scale testing facilities and to determine which of the conditions likely 

to be present in structure fires will most significantly interfere with TIC imaging performance. 

Tests were conducted with a variety of hydrocarbon fuels with widely varying smoke 

characteristics and heat release rates. The fuels included methanol, a commercial blend of 

heptane isomers, propylene, and toluene. In Table 5-1, the four test configurations are listed, 

along with the fuels and heat release rates (HRR). The layout of the structure is shown in Figure 

5—1, along with the four target/burner/TIC configurations. For these tests, methanol fires were 

placed between the TIC and the target, and within the camera’s FOV but not directly in line with 

the target. Heptane, propylene, and toluene fires were used to examine the effects of different 

smoke concentrations and upper layer temperatures on image quality. Dust and water vapor 

were generated and suspended in the air in conjunction with the various fuels. In some of these 

tests, flames were also present in the FOV. The three TIC used in each test were representative 

of each detector technology: ASi, VOx, and BST. A visible camera was also placed near the TIC 

to record target visibility. 
28

Table 5-1. Series 1 test configurations 

Configuration Number 

of Tests 

HRR 

(kW) 

TIC 

Position 

Target 

Position 

Sight 

Distance Fuel/Obscurant 

A 8 200 to 

300 

lower 

layer 

lower 

layer 3 m 

methanol, 

heptane, 

toluene, dust, 

water vapor 

B 2 175 upper 

layer 

upper 

layer 5 m toluene 

C 9 0 to 200 upper 

layer 

upper 

layer 5 m 

methanol, 

heptane, 

toluene, dust, 

water vapor 

D 13 12 to 

300 

upper 

layer 

upper 

layer 5 m 

methanol, 

heptane, 

propylene, 

toluene, dust, 

water vapor 

A full-scale structure was constructed in NIST’s Large Fire Laboratory having standard 5 cm x 

10 cm (2” x 4”) studded walls and gypsum board wall coverings, except that the walls in the 

vicinity of the fire source were covered with sheets of Marinite, a calcium-silicate based fire 

resistant material. The ceiling and floor were also covered with gypsum board or Marinite. The 

fire source was confined to various locations in a 3.7 m x 3.7 m (12 ft x 12 ft) room having a 

ceiling height of 2.4 m (8 ft). The target, shown in the inset to Figure 5—1, is comprised of 1.6 

cm (5/8 in) copper tubing through which cooling water flows, and a thin sheet of stainless steel 

as a background. Thermocouples were placed on the inlet and outlet regions of the bars and on 

corresponding locations of the background. This simple target had a single bar frequency and 

was intended to provide an estimate of the TIC response to the operating conditions by 

measurement of the contrast between the target bars and the background. All target surfaces 

were coated with a paint having an emissivity of 0.94. Note that, for this test series, each test 

contained a single fire source and target. Temperatures in the room and corridor were measured 

using Type K, 24 gauge thermocouples arranged vertically at 0.3 m intervals in a “tree” 

formation. Smoke concentrations were measured gravimetrically for some of the tests by 

drawing a known volume of smoke laden gas through a particle filter. 

The smoke and combustion gases were ventilated through a 6 m x 6 m hood and scrubbed in the 

Large Fire Laboratory’s exhaust system. In general, the repeatability of fire tests decreases as 

the scale of the tests increases; however, conditions inside the Large Fire Laboratory are 

controlled such that the full-scale fire tests are as consistent and repeatable as possible. Photos 

of the test setup and structure are shown for two test configurations in Figure 5—2. 
29

Figure 5—1. Plan view of Series 1 full-scale testing structure with inset showing the target and 

background. The target was placed on the floor in test configuration A and mounted on the wall 

1.5 m from the floor in test configurations B, C, and D. 

 

Target

Background

Water 

Lines

To Stand Pipe

Smoke 

Meter

TC 

Tree

TC 

Tree 

TC 

Tree

TC 

Tree

Burner

Config. 

C & D

Burner

Config. A 

& B

Smoke 

Meter

TC 

Tree

Smoke 

Meter

Target

Target

TIC

To data acquisition system

Config. D

Config. D

TIC

Config. A

TIC

Config. B & C

Config. A

Config. 

B & C

Dust

Dust Dust

Target with background 
30

Figure 5—2. TIC are positioned in the hot upper layer viewing a target through heavy toluene 

smoke, test configuration D (left), and in the lower layer viewing flames and high heat 

conditions, test configuration A (right).

This first test series began to characterize the high temperature or fire conditions to be studied in 

greater detail in a second series of full-scale testing. The results of this first series will be 

discussed together with the results of the second test series in Section 5.5. 

5.2. Series 2 test facility 

For this second test series, more emphasis was placed on TIC imaging performance. The 

primary goal of these tests was to determine the extent to which the heat and smoke that is 

generated in structure fires affects TIC performance. The quality of the TIC images was 

measured in terms of the Contrast Transfer Function (CTF). This performance metric is used in 

different ways for several test methods proposed in this work. Used in the context of these fullscale tests, the CTF measures the contrast differences between the hot and cold bars of the 

targets as a function of their width or frequency. This measurement will be discussed further in 

Section 5.5. 

This test series examined four different effects of fire on TIC image quality independently: 

effects of heat, effect of smoke, effects of real fuels versus idealized hydrocarbons, and the 

effects of gas versus smoke. Methanol fires having heat release rates ranging from 50 kW to 350 

kW were used to isolate the effects of heat on image quality, as this fuel produces no smoke. 

Methanol, propylene and toluene produce increasing volumes of smoke, respectively, and were 

used to isolate the effects of smoke concentration on image quality. Real furnishings such as 

carpet and cushions were tested to examine the differences between actual furnished structure 

fires and hydrocarbon fires. A Fourier Transform Infrared Spectrometer (FTIR) was used to 

characterize the gases and smoke in the corridor. 
31

For the second series of full-scale fire tests, a similar structure was built, having a long corridor 

with an adjacent fire room, except that in this case the TIC did not view the fire directly. The 

layout of this structure is shown in Figure 5—3. The TIC were placed on shelves that could be 

repositioned during the tests to view the targets from the upper layer, simulating a person 

standing, and from the lower layer, simulating a person on hands and knees. The shelves could 

also be relocated during the tests to either an alcove 6 m from the targets or the end of the 

corridor at 12 m from the targets. The targets were large bar targets that filled the end of the 

corridor, one in the upper layer and one in the lower layer. Water at approximately 20 °C flowed 

through the bars. The background for the bars was provided by hollow panels through which 

flowed hot water at approximately 50°C. All target and background surfaces were coated with 

paint having an emissivity of 0.94. An attempt was made to keep the target and background 

temperatures as constant as possible, however, this was very difficult to achieve during some of 

the more intense fire tests. Thermocouples were placed at numerous locations on the bars and 

the background. In addition to the bar targets, a heated mannequin fitted with fire fighter turnout 

gear was placed on the floor at the end of the corridor. 

The structure was fitted with thermocouple trees and smoke measurement instruments. Smoke 

concentration measurements were made gravimetrically or, in a few cases, with a smoke meter 

that could slide along tracks down the length of the corridor. In addition to these measurements, 

O2, CO and CO2 volume fractions inside the fire room and corridor were measured using a 

Servomex 540A and Seimens Ultramat 6 gas analyzers, respectively. The heat release rate was 

measured by analyzing the composition, temperature and flow rate of the exhaust gases [46]. 

Figure 5—3. Plan view of Series 2 full-scale fire test configuration with TIC viewing IR targets 

having at two distances. A heated mannequin in fire fighter turnout gear was also placed in the 

FOV.

ISO

Room

(2.4 m x 3.6 m)

T

CI

TIC

1 m

3.6 m 2.4 m

fire

vent 

air supply

TC

Gas monitors:

O2, CO, CO2 Herman

(Mannequin) vent 

angle = 20o

IR 

target

12 m

corridor height = 2.4 m

smoke meter tracks

TC

TC3

TC

2.4 m
32

The collection of TIC used in this test series was comprised of 8 fire fighting TIC, of which 2 

had BST detectors, 2 had ASi detectors, and 4 had VOx detectors. In addition to the fire fighting 

TIC, 2 scientific infrared cameras and 2 visible cameras were tested. The cameras were rotated 

through a sequence of four positions during each test, such that each TIC viewed the targets 

through the lower layer and through the upper layer at each of the two sight distances for at least 

5 minutes in each position. For the unsteady tests this system made it difficult to maintain 

repeatability because the fire intensity grew and declined as the TIC were moved from position 

to position. In Figure 5—4, a photo of the TIC shelves at the end of the corridor are shown on 

the left and the two bar targets and mannequin are shown in infrared on the right. 

The infrared targets can be seen in the background on the right of Figure 5—4. The width of the 

hot/cold bars in the infrared targets is 10 cm, 7.5 cm, and 5.0 cm, which were viewed at sight 

distances of 6 m and 12 m. The image on the right in Figure 5—4 shows these bars: the three 

left-most bars in this image have a frequency of 0.03 cyc/mrad at 6 m (0.06 cyc/mrad at 12 m), 

the next three bars to the right have a frequency of 0.04 cyc/mrad at 6 m (0.08 cyc/mrad at 12 

m), and the four right-most bars have a frequency of 0.06 cyc/mrad at 6 m (0.12 cyc/mrad at 12 

m). The redundant frequency of 0.06 cyc/mrad enabled an examination of sight distance effects. 

The fire heat release rate and the peak CO2 volume fraction, peak temperatures, and smoke 

concentrations that were measured in the line of sight between the TIC and the infrared targets 

are reported in Table 5-2. In some cases these measurements were made in the fire room, and in 

some cases they were made in the corridor, where the first responder would be operating, see the 

notes in Table 5-2. 

 

Figure 5—4. The TIC were mounted on shelves which were repositioned midway through the 

tests (left). Two bar targets were used, one in the upper layer and one in the lower layer, along 

with a heated mannequin in fire fighter turnout gear, shown in infrared (right).
33

Table 5-2. Series 2 test configuration.

Number of 

Tests HRR (kW) TIC Position Target Position Site Distance (m) Fuel 

2 50 upper and 

lower layers 

upper and 

lower layers 6, 12 methanol 

2 350 upper and 

lower layers 

upper and 

lower layers 6, 12 methanol 

1 8 upper and 

lower layers 

upper and 

lower layers 6, 12 propylene 

3 32 upper and 

lower layers 

upper and 

lower layers 6, 12 propylene 

3 200 upper and 

lower layers 

upper and 

lower layers 6,12 toluene 

1 200 max upper and 

lower layers 

upper and 

lower layers 6, 12 single wood crib 

1 300 max upper and 

lower layers 

upper and 

lower layers 6, 12 double wood crib 

3 600 max upper and 

lower layers 

upper and 

lower layers 6, 12 cushions 

3 2300 max upper and 

lower layers 

upper and 

lower layers 6, 12 Carpet/padding/wood 

5.3. FTIR measurements 

The intervening media between a target and an imager may impact the view of a TIC through 

emission, absorption, or scattering. The current generation of commercial TIC detect in the long 

wave-infrared region of the spectrum, from wavenumbers of about 700 cm-1 to 1250 cm-1

(wavelengths 14 μm to 8.0 μm, respectively). As mentioned in Section 2.1, this region is 

selected for use because there is minimal overlap with the spectra of the most common 

combustion species. The spectral response of TIC may fluctuate between different technology 

types, and thus imager performance may be differentially affected by the presence of a hot layer 

of combustion products including smoke. In a typical compartment fire, smoke may easily 

obscure the presence of a human in the visible spectrum (0.4 μm to 0.7 μm). The impact of an 

intervening smoke aerosol on an imager’s view depends on its temperature and its concentration 

as compared to the temperature and emissivity of a target. Smoke may absorb and scatter 

thermal radiation, but will not emit significantly. 

Chemical compounds that give rise to a dipole moment absorb and emit infrared radiation at 

unique and characteristic frequencies. In the experiments reported here, a portable Fourier 

Transform Infrared Spectrometer (FTIR) was used to characterize the line of sight radiative 

emission in the infrared, from 650 cm-1 to 5000 cm-1 (15.4 μm – 2.0 μm), covering the entire 

spectral range of a typical TIC. The FTIR was positioned outside the corridor and was aligned to 

detect the same bar target that the TIC were positioned to view, looking through the hot upper 

layer of the full 12 m corridor length. The measurements were made at 0.5 cm-1 resolution, 
34

which resulted in a sampling rate of about 1 scan/s. The measurements were stored as averages 

of sixty scans, or 1 min of data. The FOV was collimated, having a diameter on the order of 5cm 

at the 12 m distance. The results of this measurement are presented in section 5.5.3.

5.4. Hose stream experiments 

Full-scale tests of the effectiveness of different types of hose streams were conducted. The 

objectives of these experiments were to understand the spray characteristic and suppression 

effectiveness of smooth bore (jet) and wide angle (fog) hose stream sprays, and to use this 

information to enhance the fire prediction capability of the Fire Dynamics Simulator (FDS) 

developed and maintained at NIST [47]. While these experiments were not intended to further 

the goals of the thermal imaging project, they offered an opportunity for collection of qualitative 

information about TIC imaging performance in the presence of water sprays and wetted surfaces. 

The testing facility consisted of a 7.0 m x 7.0 m x 3.3 m compartment with a 4.6 m x 2.1 m 

opening. A heptane spray burner was located in one rear corner and an array of water collection 

apparatus was located in the other rear corner. The heat release rate of the fires was 2.2 MW. 

The water nozzles were oriented to spray diagonally across the enclosure into the water 

collection area. The water pressure and flow rate were varied throughout the test series. Gas 

temperatures and velocities, heat flux, and the mass of applied water were measured. Three 

thermal imagers were set up outside the enclosure to view, through the water sprays, a thermal 

target mounted on the back wall midway between the fire and the water collection apparatus. 

This arrangement is shown in Figure 5—5, with the TIC mounted on a rack covered in aluminum 

foil on the far left side of the image. The simple thermal target was comprised of a heated 

copper plate behind copper tubing through which flowed cold water. The temperature of the 

target background varied from 55 °C to 120 °C during the course of a typical 10 min test, while 

the cold tubing varied from 15 °C to 34 °C. 

As mentioned above, these hose stream tests were intended to provide qualitative information 

about the effect of water sprays and wetted surfaces on image quality. The effect of flames in 

the field of view was also a significant factor in image quality. The results of these experiments 

are discussed in subsection 5.5.4. 
35

Figure 5—5. Visible image of typical hose stream test set up. Three TIC (behind foil on far 

left) are viewing a thermal target through a fog spray in the presence of a 2.2 MW heptane fire. 

5.5. Full-scale experimental results 

In broad terms, both full-scale test series (Series 1 and Series 2) were intended to provide 

information about the thermal environment in which TIC are expected to function. Both test 

series also investigated TIC imaging performance as a function of various environmental 

parameters, with the first test series acting as a scoping exercise for the second, more substantial 

test series. This information was used to determine which of the conditions likely to be present 

in structure fires will most significantly interfere with TIC imaging performance and to design 

bench-scale testing facilities. 

Since the thermal environments that occurred during both full-scale test series are similar in 

nature, they will be presented together in the following text. Smoke and post combustion gas 

concentrations and temperatures, and surface temperatures are of particular interest as they tend 

to have the most significant impact on TIC imaging performance. Recall from Figure 2—1 that 

CO2 and water vapor can potentially interfere with the transmittance of radiated energy, 

particularly around the outer edges of the TIC sensing region (8μm and 14 μm). At the time 

these full-scale tests were conducted, the large fire laboratory did not have the ability to collect 

water vapor concentration data. In Table 5-3 the thermal environment data are presented for 

both full-scale test series. Note that CO concentrations were measured but not reported, as CO 

has a minimal influence on TIC imaging performance. 

Thermal 

Target 
36

Table 5-3. Thermal environment (where applicable uncertainties are determined as stated in section 7.5 

and expressed with a coverage factor of k=2).

Heat Release 

Rate Q& (kW) Fuel Type 

Peak CO2

Concentration 

(vol %)

Peak 

Temperature 

(°C)

Peak Smoke 

Density (g/m3

)

200 Methanol nr 1911 (± 3 %) 0.041 (± 10 %) 

200 Heptane nr 203 1 0.101

175 Heptane nr 180 1 0.111

175 Toluene nr 140 1 0.761

175 Heptane nr 190 1 nr 

12 to 21 Propylene nr 83 1 0.14 1

33 Propylene 0.5 2 (± 10 %) 62 3 0.15 3

200 Toluene 2.9 2 141 3 0.46 3

175 Toluene nr 123 3 0.45 3

350 Methanol 5.9 2 220 3 nr 

200 Methanol nr 184 3 0.1 3

100 Methanol nr 128 3 0.1 3

50 Methanol 0.6 2 56 3 nr 

300 (Peak) Double wood crib 6.5 2 150 3 nr 

200 (Peak) Single wood crib 2.0 2 110 3 0.01 3

600 (Peak) Cushions 5.7 2 142 3 0.75 3

nr Wood crib over carpet and 

padding 9.3 2

 200 3 0.58 3

1. Average peak temperature and smoke density values measured in room of fire origin. 

2. Average peak CO2 concentration measured in corridor adjacent to room of fire origin. 

3. Average peak temperature and smoke density values measured in corridor adjacent to room of fire 

origin. 

The qualitative TIC imaging performance results obtained for the first full-scale test series 

indicate that the presence of dust and water vapor do not significantly impair the imaging 

performance of TIC, even in high concentrations. Water mist, sprays, and wetted target surfaces 

were not tested at this time. Hot smoke and flames in the FOV, however, do have a negative 

impact on TIC imaging performance. It was found that the TIC detector technologies tested, an 

ASi, a VOx, and a BST, did not perform consistently across the different test conditions. 

Although the detector technology alone is not a sufficient indicator of TIC imaging performance, 

it appeared that low heat conditions were more amenable to microbolometers (VOx and ASi) 

than BST detectors. Conversely, conditions in which a wider range of gas and surface 

temperatures are present appear to be more suitable for BST detector technology, as seen in 

Figure 2—3. It should be emphasized that the TIC optical system, electronic processing, and 

display quality make large contributions to overall image quality. Advances in microbolometer 

technology in recent years have improved TIC performance greatly and other new detector 
37

technologies are being developed that may prove to perform much better than anything currently 

available in the fire fighter market. 

The above observations were used to design the test matrix for the second full-scale test series. 

For these imaging performance results the figure of merit is the Contrast Transfer Function 

(CTF), which is measured for the worst case test condition: upper layer position for both the TIC 

and the target. The video signal is averaged for 5 minutes at each of the two sight distances. The 

error bars in the following figures are derived from the standard deviation from the mean image 

pixel intensity, with a coverage factor of 2. The images were collected from digital videotape 

and have an 8-bit signal depth. The CTF is calculated using this equation: 

 Bitdepth

I I CTF max − min = (1) 

where Imax and Imin are the maximum and minimum image pixel intensities, respectively, and 

Bitdepth is the maximum possible image pixel intensity determined by the output signal. In this 

case Bitdepth = 28

 = 256. The CTF can vary from 0 to 1, with a value of 0 indicating that there is 

no contrast in the image and a value of 1 indicating that the maximum possible contrast is 

present. It is expected that the CTF will decrease with increasing bar frequency as the TIC reach 

their limits of spatial frequency and the bar frequency goes into the signal noise (nonuniformity). 

Ordinarily, the CTF curve is normalized to a “zero” frequency, making it strictly a spatial 

resolution metric. This was not done for these tests because the absolute value of the contrast 

was also of interest. 

Recall that there were five unique bar frequencies in the test configuration, with a redundant 

frequency at 0.06 cyc/mrad resulting from the bar dimensions combining with the sight distances 

in an equivalent way. This redundancy allows observation of the effects of sight distance, in 

other words, the difference between viewing a set of 5 cm thick bars from 6 m and viewing a set 

of 10 cm thick bars from 12 m is attributed to the TIC sight distance. 

5.5.1.Heat effects 

The two major areas of investigation for TIC image quality are heat effects and smoke effects. 

Results are reported for a total of six TIC, with two TIC representing each of the three detector 

technologies. In the following three figures, comparisons are made of TIC employing BST, 

VOx, and ASi detectors in two heat conditions. The fuel for these two test conditions was 

methanol, which produces a minimal amount of smoke, burning at a constant HRR of 50 kW and 

350 kW. Recall from Table 5-3 that the maximum gas temperature in the TIC line of sight was 

56 °C for the 50 kW fires, and 220 °C for the 350 kW fires. 

The heat test results for the BST-type TIC are shown in Figure 5—6. These two TIC are the 

same model, purchased approximately 4 years apart. Significant differences in test results can be 

attributed to maintenance needs of the older TIC and to upgraded electronics in the newer TIC. 

The older TIC (TIC A) was sent to the manufacturer several months after this test series for 

maintenance. The detector array size for both TIC is 320 x 240 sensing elements. TIC B shows 

very little difference in CTF due to sight distance, and in fact no CTF degradation is apparent in 

the 50 kW case until the highest bar frequency is measured, whereas the CTF for TIC A drops 

considerably at 0.06 cyc/mrad, indicating a large sight distance effect, and continues dropping to 
38

Figure 5—6. Comparison of heat effects, BST detector technology. These two TIC differ only 

in age, both having a 320 x 240 detector array. (where applicable uncertainties are determined 

statistically as stated in section 7.5 and reported with a coverage factor of k=2)

virtually zero at 0.12 cyc/mrad. The results for TIC B for the 350 kW case is somewhat 

puzzling. Here the CTF jumps higher at 0.06 cyc/mrad, meaning that the bars were more distinct 

to the TIC from a longer distance than they were at the shorter distance. This is the only time in 

this test series that this result occurred. In spite of this unusual result, TIC B still performed 

better than TIC A throughout the bar frequency range, although there was a lot of deviation in 

the signal, as seen in the length of the error bars. Neither TIC responds to increasing bar 

frequency at the 12 m sight distance for the 350 kW case. 

The heat test results for the VOx-type TIC are shown in Figure 5—7. Both TIC used in these 

tests utilize a 160 x 120 pixel detector array that is produced by different detector manufacturers. 

The TIC themselves are also produced by different manufacturers, employing different optics 

and electronics systems. TIC C and D both show the characteristic decline in CTF with 

increasing bar frequency for the 50 kW case, although only TIC D is sensitive to sight distance 

effects. The absolute value of the CTF for TIC D at a bar frequency of 0.03 cyc/mrad in the 50 

kW case compares well with that of TIC B above, however the CTF of TIC B remains much 

higher throughout the rest of the frequency range. This indicates that TIC B can distinguish finer 

image detail (has a larger spatial resolution). In the 350 kW case, the CTF of TIC D is 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC A, 350kW

TIC B, 350kW

TIC A, 50kW

TIC B, 50kW
39

significantly higher than that of TIC C at the shorter sight distance, but both TIC perform 

virtually the same at the longer sight distance, with no response to increasing bar frequency. 

Again, TIC D shows a sensitivity to sight distance that is missing in TIC C. 

The heat test results for the ASi-type TIC are shown in Figure 5—8. Both TIC used in these 

tests utilize a 160 x 120 pixel detector array that is produced by the same detector manufacturer 

but are not the same detector model. The TIC themselves are produced by different 

manufacturers, employing different optics and electronics systems. In Figure 5-8 the general 

shape of the curves for ASi-type TIC is similar to those in Figure 5—7 for VOx-type TIC, 

although the overall CTF values are slightly lower. In general, the microbolometers tested, both 

VOx and ASi, performed at a lower level in these tests than the BST-type TIC. This difference 

can be attributed in part to the smaller detector arrays and to the responsivity of the sensing 

materials. In the 50 kW case, TIC E performed better at the lower bar frequencies but about the 

same as TIC F beginning at 0.06 cyc/mrad. In the 350 kW case, TIC F does not show a sight 

distance effect, however, given the length of the error bars, the imaging performance of both TIC 

is considered to be statistically the same. Although the CTF values for the two TIC used in these 

tests are lower than the other TIC, ASi is attractive to TIC manufacturers because it is less 

expensive and can be housed in a smaller form factor. One of these TIC is a helmet-mounted 

device, which allows fire fighters to keep both hands free. 

Figure 5—7. Comparison of heat effects, VOx detector technology.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC C, 350kW

TIC D, 350kw

TIC C, 50kW

TIC D, 50kW
40

Figure 5—8. Comparison of heat effects for ASi detector technology.

In summary, these results show that some TIC are sensitive to sight distance effects when 

viewing a target through hot gases, while others are not. TIC with 320 x 240 detector arrays 

have higher CTFs at higher bar frequencies than TIC with 160 x 120 detector arrays indicating a 

larger spatial resolution of the camera. At the time of this writing, there are no ASi-type TIC that 

have detector arrays larger than 160 x 120 available on the fire fighting market. There are, 

however, VOx-type TIC available with 320 x 240 detector arrays, but none were available to the 

researchers at the time these tests were conducted. This type of testing, under more controlled 

conditions and in a bench-scale testing facility may be useful to indicate the need for TIC 

maintenance. Imaging performance is an important criterion to aid TIC users in their purchasing 

decisions, but it is not the only thing to consider. TIC size and weight, cost, handheld vs hands 

free, and other practical considerations also play important roles in determining the TIC that best 

matches the needs of a particular fire department. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC E, 350kW

TIC F, 350kW

TIC E, 50kW

TIC F, 50kW
41

5.5.2. Smoke effects 

For these comparisons, the 50 kW test, which produces very little smoke, is again used as the 

base case. The light smoke condition is produced by 32 kW propylene fires, in which case the 

smoke concentration was measured at 0.143 ±0.02 g/m3

. The heavy smoke condition is 

produced by 200 kW toluene fires, where the smoke concentration was measured at 0.671 ± 

0.09 g/m3

. The same six TIC, positioned in the same locations as in the previous tests were used. 

The HRRs for the 50 kW methanol and 32 kW propylene fires make them better comparisons 

than the 200 kW toluene fires, which would also incorporate heat effects. The toluene fires, 

producing both high heat and smoke environments, are included as a worst-case condition. 

The smoke test results for the BST-type are shown in Figure 5—9. Sight distance effects play an 

important role in image quality for both these TIC, rather than only TIC A, as was the case when 

heat only was being examined in Figure 5—5. For TIC B, the shorter sight distance combined 

with the light smoke condition appears to have no effect on the CTF. The heavy smoke 

condition, however, significantly reduces the CTF at the shorter sight distance for both TIC. As 

expected, increased smoke concentrations cause a decrease in the ability of these TIC to 

distinguish detail in a thermal scene. The heavy smoke condition for TIC B, and both smoke 

conditions for TIC A indicate that neither TIC is responding to increasing bar frequencies at the 

longer sight distance. 

Figure 5—9. Comparison of smoke effects for BST detector technology.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC A, 50kW

TIC B, 50kW

TIC A, Light Smoke

TIC B, Light Smoke

TIC A, Heavy Smoke

TIC B, Heavy Smoke
42

The smoke test results for the VOx-type TIC are shown in Figure 5—10. Sight distance again 

appears to play an important role in TIC imaging performance, especially in the light smoke 

condition for both TIC tested. In the heavy smoke condition, neither TIC performed well 

regardless of sight distance. As with the BST-type TIC shown in Figure 5-9 above, the VOxtype TIC response to increasing bar frequencies disappears or is negligible in heavy smoke, 

particularly at the longer sight distance, producing about the same as or slightly lower CTF

values than the BST-type TIC in these conditions. 

The smoke test results for ASi-type TIC are shown in Figure 5—11. As with the comparison of 

heat effects between ASi and VOx-type TIC, the smoke effects are similar in the general shape 

of the CTF curves except that the CTF values are somewhat lower for ASi-type TIC, especially 

in the lower bar frequency range. Again, similar to the VOx-type TIC, it can be seen that these 

two ASi-type TIC are not useful tools in heavy smoke and heat conditions. When comparing the 

light smoke results with those of the VOx-type TIC, the ASi-type TIC show very similar 

performance. 

In summary, these results show that all of the TIC tested were sensitive to sight distance effects 

when viewing a target through smoke. The microbolometers were unable to discern the target 

bars in high heat and smoke conditions even at low bar frequencies, while only one of the BSTtype TIC was able to see the target bars at low frequencies. In light smoke conditions, the 

performance of the four microbolometers was similar, but only exceeded the performance of one 

of the BST-type TIC at bar frequencies above 0.06 cyc/mrad. 

Figure 5—10. Comparison of smoke effects for VOx detector technology.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC C, 50kW

TIC D, 50kW

TIC C, Light Smoke
43

Figure 5—11. Comparison of smoke effects for ASi detector technology.

5.5.3.FTIR measurement results 

Figure 5—12 shows the measured relative radiant intensity as a function of wavenumber during 

an experiment in which the burning fuel source was a wood crib over carpet and padding (see the 

last entry in Table 5-3). FTIR results are shown at 0min and 4 min after ignition in the 

experiments. The relative FTIR signal increased significantly with time. Table 5-3 shows that 

the upper layer temperature in the experiment obtained a peak value of about 200 °C, which 

occurred about 4min into the experiment. The upper layer temperature at 4 min suggests that the 

experiment was a Class III thermal condition at that time (see Table 4-2). At early times in this 

experiment, and for some of the other experiments, Class I and Class II conditions were tested. 

The FTIR measurement of a blackbody source at 200 °C (Type B uncertainty of ±5 °C, based on 

accuracy of temperature measurements) is also shown in Figure 5—12, which is consistent with 

the experimental spectrum. This suggests that the smoke was optically thick in the hot upper 

layer of the corridor. Band absorption by water vapor is seen for wavenumbers between about 

1300 cm-1 and 2000 cm-1 (7.7 μm and 5.0 μm ). The figure shows recognizable emission 

signatures for individual species during the experiment, but not in the spectral region in which 

TIC are sensitive, recall from discussion of Figure 2-1, which reinforces the reason TIC are 

designed to operate in this portion of the infrared spectrum. The results for the other fuels types 

yielded similar results, as little band radiation was observed in the portion of the spectrum where 

the TIC are sensitive. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 0.12

CTF

Frequency (cyc/mrad)

TIC E, 50 kW

TIC E, Light Smoke

TIC F, Light Smoke

TIC E, Heavy Smoke

TIC F, Heavy Smoke

TIC F, 50 kW
44

Figure 5—12. The relative FTIR signal measured at two times during an experiment burning 

carpet, padding, and wood. For comparison, measurement of the relative signal of a blackbody 

source at 200 °C (±5 °C, as per manufacturer’s documentation) is also shown.

5.5.4.Hose stream results 

The three TIC chosen for this work were selected because they were available at the time the 

hose stream tests were conducted. Therefore, due to a temporary lack of availability of one type 

of TIC detector, the usual mix of BST, VOx and ASi detector technology was not used. In 

Figure 5—13 below, the center image was produced by a BST-type TIC and the top and bottom 

images were produced by two different manufacturers’ ASi-type TIC. 

Note in Figure 5—13 that there is a distinct difference in the amount of detail between the center 

image and the others, and that, while the top and bottom images are relatively similar, there are 

also noticeable differences as well. For example, the water spray is barely visible in the right 

image. Other observations were: prior to ignition of the fire, all three TIC showed gray scenes 

with only the target and the pilot light for the fire being distinctly visible. The cold target bars 

were visible only in the BST-type TIC images prior to fire ignition. After the fire was ignited 

but prior to the application of water, the two ASi-type TIC behaved somewhat similarly. The 

cold target bars were barely visible in one case and quite visible in the other case, and then the 

entire target turned dark while the rest of the image was saturated (bright white) as the 

compartment surface temperatures rose and saturated the TIC detectors. The BST-type TIC 

continued to show the target bars and a gray scene elsewhere in the image. During the 

application of water sprays, as shown in Figure 5—13, the target is not readily apparent, 

however, it does appear to some degree in the CTF calculations for all three TIC. 

 

0

20000

40000

60000

80000

100000

120000

500 1000 1500 2000 2500 3000

Wavenumber (cm

-1)

Relative Signal

4 min

0 min

BB at 200 C

 TIC Range 
45

Figure 5—13. Thermal images of a scene in which a fog spray is directed toward a wall in front 

of a 2.2 MW heptane fire. A BST-type TIC produced the center image and ASi-type TIC from 

different manufacturers produced the two other images.
46

Figure 5—14. CTF of a thermal target viewed by three TIC through fog and straight (jet) sprays 

with a 2.2 MW fire in the field of view. The error bars represent the standard deviation of the 

CTF with a coverage factor of 2 (95 % confidence). 

 

0

0.05

0.1

0.15

0.2

0.25

0.3

BST ASi-1 ASi-2

CTF

TIC Detector Type

Fog Spray

Straight (jet) Spray
47

The CTF was calculated during the water spray application; images that were captured from 

digital videotape at a rate of 30 frames/sec for a period of 40 s were averaged to determine the 

CTF. The CTF data are presented in Figure 5—14. The error bars represent the standard 

deviation of the CTF measurements with a coverage factor of 2 (95 % confidence). 

Although the bars of the thermal target observed in images on the BST-type TIC display and in 

the videotaped images appeared to be more visible than those of the other two TIC, the data 

displayed in Figure 5—14 shows that one of the ASi-type TIC provided significantly better 

target contrast in the jet spray case. It is possible that the jet was not positioned directly between 

the TIC and the target when the data was collected, in which case the obscuring effect would be 

minimal. It should be noted that CTF values below about 0.2 indicate contrasts that are only 

marginally useful to TIC users since they are likely to be in the noise floor of the camera caused 

by image nonuniformity. Human perception of contrast, noise, spatial resolution, and other 

image characteristic are not being studied as a part of this work. 

5.6. Consolidation of test condition information 

Based on the survey of previous work and the full scale investigations discussed above TIC 

activities have been categorized in Table 5-4. Table 5-4 is based on the thermal classes noted 

before in Table 4-1 but has been modified to more accurately reflect the specific situations 

necessary to be evaluated for TIC performance. The test results reported in Table 4-2 provides 

guidance as to the nature of the thermal environment that might be encountered while the TIC 

operators are engaged in fire fighting activities such as those listed in Table 4-3. Existing 

standard requirements for design robustness tests are embedded in the development of the four 

thermal classes, e.g., a TIC used in a Class III environment should be able to function properly 

under the same conditions in which fire fighter turnout gear is tested (e.g. withstand temperatures 

up to 260 °C for 5 min per NFPA 1971 [32], see Appendix B). 

With respect to image quality, there are two general areas of interest. First, the ability of a TIC 

to discern detail in a thermal scene has important implications regarding the suitability of that 

TIC to perform certain activities. For example, being able to see a victim on the floor as 

illustrated in Figure 5—4 or being able to see through a hose stream as illustrated in Figure 5—5 

and Figure 5—13. Second, the thermal sensitivity of the TIC is important, because the range of 

surface temperatures that may co-exist in the FOV may be very wide or very narrow. To 

illustrate the way these two performance metrics interact, recall the earlier example of a TIC 

used to observe a human with flames in the FOV illustrated below in Figure 5—15. If the spatial 

resolution (ability to discern detail) is poor, the TIC user may not be able to see any difference 

between a human and building clutter, regardless of the thermal sensitivity of the TIC. If the 

thermal sensitivity is poor, the TIC user may not be able to differentiate items having small 

temperature differences, regardless of the detail in the TIC images. Table 5-4 consolidates the 

operating environment, expected TIC activities, and imaging performance needs with each 

thermal class. A natural outgrowth of Table 5-4 is the selection or development of appropriate 

imaging performance metrics and tests that meet the needs of the fire service community. This is 

the subject of section 6 on imaging performance metrics and test methods, where the proposed 

tests in Table 5-4 are explained in detail.
48

 

 

Figure 5—15. Identical scene from full scale test series two observed with three different 

cameras. From top to bottom VOx, ASi, and BST TIC are utilized to view the same scene at the 

same time consisting of a mock victim on the floor with smoke and flames in the field of view.
49

Table 5-4. Proposed TIC Testing Conditions. 

Class

Class I

(water, fog, or snow 

possible, minimal heat, 

smoke and flames)

Class II

(elevated temperatures, 

water, dust, smoke and 

flames may be present)

Class III

(high temperatures and smoke 

concentrations, flames, dust, 

and water are likely)

Activity

Hazmat 

Medical 

Motor vehicle accident 

Search 

Overhaul 

Size up 

Forensics 

Preventative maintenance 

Search 

Overhaul 

Forensics 

Wildland fires 

Size up 

TacTIC 

Communication 

Search

Proposed 

Test

Measure smallest ΔT at 

nominal target temperatures of 1 °C, 30 °C, and 

100 °C. 

Also, measure spatial 

resolution and 

nonuniformity of image. 

Measure smallest ΔT at 

nominal target temperature 

of 160 °C. 

Also, measure largest

overall ΔT at which target 

with small ΔT is visible. 

Also, measure spatial 

resolution and 

nonuniformity of image. 

Measure smallest ΔT at 

nominal target temperature 

of 260 °C. 

Also, measure spatial 

resolution and 

nonuniformity of image.

Note: TIC would not likely be used in a Class IV thermal environment. First responders operating in 

Class IV thermal conditions would be in retreat, rather than viewing the scene through a TIC, although 

one might reasonably expect to view a Class IV scene from a distance. 
50

6. PERFORMANCE METRICS AND TEST METHODS 

While this work focuses on imaging performance metrics and test methods, it is also necessary to 

consider the effects of performance requirements for TIC design robustness because image 

quality may be used as the pass/fail criteria for many of these tests used by standards 

organizations. For example, an environmental temperature stress test may require the TIC to be 

exposed to an elevated temperature of 60 °C for 4 hours, then be exposed to a low temperature of 

–20 °C for 4 hours, and then experience a thermal shock (changing from –20 °C to 60 °C within 

5 min.). Immediately after each of these three procedures the thermal image produced by the 

TIC is evaluated to determine whether the procedure had an adverse effect on image quality. 

The procedure for examining the effect of a design robustness test on image quality is the Image 

Recognition Procedure and will be discussed in section 6.1. The images used to evaluate image 

quality, other than the Image Recognition Procedure, are collected directly from the TIC display. 

A brief description of the setup used to capture and process these images is provided in section 

6.2. 

There are five image quality performance metrics, along with their accompanying test methods, 

which were developed to measure various aspects of image quality as presented to the end user 

on the TIC display. Going back to Table 4-1, after considerable investigation, several tests were 

proposed in common with Class I, II, and III environments. They are contrast, image 

nonuniformity, spatial resolution, and thermal sensitivity. In addition, a new test was developed 

for Class II environments: the effective temperature range (ETR) test, which measures TIC 

performance with a wide range of temperatures in the FOV. The ETR is only included for a 

Class II environment because the Class II environment encompasses the largest temperature 

range and overlaps both the Class I and Class III environments. These science-based, objective 

tests are described in detail in sections 6.3 through 6.7. Test results, which highlight the range 

and variability of TIC imaging performance, are presented and discussed briefly in section 7. 

 

6.1. Image Recognition Procedure 

The Image Recognition Procedure (IRP) is a relatively simple method of determining whether a 

design robustness test has adversely affected the image quality of a TIC. Image recognition may 

be included as a pass/fail criterion for other physical performance tests: Environmental 

Temperature Stress, Immersion/Leakage, Vibration, Impact-Acceleration, Corrosion, Heat 

Resistance, and the “Torture Test”. For the IRP, the test operator uses the TIC under test to view 

a reflective test target with converging lines in the vertical and horizontal directions is viewed at 

a distance of 1m, as shown in Figure 6—1 and Figure 6—2, and records the vertical and 

horizontal values at which the lines appear to blur together. The reflective surface of the target 

(white areas in Figure 6—1) has an emissivity (ε) ≤ 0.1 and the black matte background has ε ≥

0.9 in the 8 μm to 14 μm wavelength range. The target reflects radiation from an extended area 

blackbody or similar heat source. The resulting image recognition values, each of which 

correspond to a nondimensionalized spatial resolution, must exceed the minimum values 

established in the performance requirements. The target design for this procedure was adapted 

from a portion of the ISO 12233 test chart [28]. 
51

Figure 6—1. Reflective test target used for 

image recognition tests. The test target 

dimensions are 61 cm (24 in.) in each 

direction. The white markings shown here are 

highly reflective foil with an ε ≤ 0.1 and the 

background is foam core with a black matte 

finish having an ε ≥ 0.9. 

Figure 6—2. An example viewing 

configuration is also shown (right) with the 

TIC positioned 1m away from the IRP target 

surface.

Before any other testing begins on the TIC, the test operator performs the IRP in order to 

establish that the TIC can provide an image of acceptable quality. If the TIC cannot provide 

such an image there is no point in further testing. If the image is acceptable, the TIC is tested as 

required by the standard. After each of the design robustness tests is performed, the IRP is 

conducted to ensure that the TIC is still capable of providing an acceptable image. In some cases 

additional pass/fail criteria are stipulated, for example in a Immersion/Leakage test, the TIC may 

be required to provide an acceptable image and also have no water inside its electronics 

compartment. 

The image recognition test target is situated as illustrated in Figure 6—2. The test is conducted in 

a thermally stable 25 °C (77 °F) environment, surrounded by a shroud (not shown), and reflects 

only heat generated by a blackbody or similar extended area source set at 30 °C (86 °F). The 

TIC under test is positioned 1 m from the test target, such that the test target is visible and in 

focus on the TIC display. The test operator views the TIC display and determines the location 

where the vertical and horizontal converging lines become indistinguishable. These vertical and 

horizontal values must exceed the minimum values established in the performance requirements 

through the standards development process. 

Heated Surface 

TIC Viewing IRP Target 

Reflective IRP Target 

 30°C 
52

6.2. Image capturing procedure 

In keeping with the treatment of TIC as black boxes, it is necessary to evaluate the TIC in a 

manner consistent with their use by the fire service. Thus, the images that are presented to the 

user on the display are the same images that are examined to determine whether the TIC meets 

the imaging performance requirements as developed through the standards development process. 

In Figure 6—3, a thermal bar target (shown on the right) is viewed by a TIC under test, while the 

TIC display is viewed by a high resolution, calibrated visible camera (shown on the left). 

Through the development of standard testing methodology, the performance of the visible 

camera and lens to be used by third-party testing organizations will be available to the TIC 

manufacturers so that they can design and build a mounting bracket to position the visible 

camera such that it generates an optimized view of the TIC’s entire display area. 

6.3. Contrast 

In the context of fire service applications, contrast measurements determine whether the TIC is 

capable of producing sufficient contrast for the user to identify objects of interest such as victims 

and potential fire hazards. With respect to a grayscale image, contrast is a measure of the 

relative luminance (or pixel intensity) of portions of the image. Contrast in an image can be 

measured several ways, depending on the type of test target used and the reason for the 

measurement. The definition of contrast is: 

Bitdepth

C 2σ = , (1) 

Figure 6—3. Schematic diagram of image capturing setup. As the TIC views a thermal target, a 

high resolution visible camera is focused on the TIC display. A mounting bracket (not shown) is 

to be provided by the TIC manufacturer to optimally position the visible camera. 

Visible 

Camera 

TIC 

Thermal 

Target 
53

where C is the contrast, σ is the standard deviation of pixel intensities, and Bitdepth is the pixel 

intensity resolution. Most, if not all, currently available TIC displays have an 8-bit pixel intensity 

resolution, in which case the Bitdepth = 28

 = 256. There are two applications of contrast 

measurements in this work: large area contrast, to which this section applies; and bar contrast, 

which is part of the effective temperature range (ETR) measurement discussed in section 6.4. 

Different parts of the same test target, shown in Figure 6—4, are used for both contrast 

measurements, which are collected concurrently. The target consists of three blackbodies and a 

heated bar target. A room temperature blackbody, 25 °C, can be seen in the right of Figure 6—4, 

a 25 °C blackbody with 30 °C bars is in the center of Figure 6—4, and a hot blackbody, which 

has its temperature varied in a range from 25 °C to 350 °C (the maximum range of the 

blackbody) can be seen in the left of Figure 6—4. A detailed discussion of the development of 

contrast as it applies to fire service TIC can be found in [48]. 

The standard deviation of the combined pixel intensities within the leftmost and rightmost areas 

of the test target shown in Figure 6—4 (pixels exposed to T2 and Tsur, which have the same size 

areas) is calculated, then divided by the Bitdepth to determine the large area contrast. The bars 

in the middle of the test target are ignored for large area contrast measurements. The large area 

contrast reported for this test is the maximum contrast obtained while T2 is ramped from ambient 

to Tmax at a rate of 10 °C/min. T2 is the temperature of a surface of area large enough to cause 

the TIC under test to shift sensitivity mode, if the TIC is designed to shift mode. The minimum 

size of the T2 area may vary from TIC to TIC, depending on the specific algorithm used to 

trigger a mode shift. It is important to confirm that T2 has a sufficiently large area prior to 

conducting the contrast/ETR tests. 

The ambient surface area (Tsur) is held constant at 25 °C ± 1 °C throughout the test. Tmax is the 

temperature to define the scene temperature range within which TIC should be expected to 

provide useful images. The areas within the dashed lines represent the middle 90 % of each 

temperature-controlled surface area and are specified to avoid edge effect issues. The large area 

contrast obtained throughout the test period is compared with the range of acceptable pass/fail 

criteria, determined by the Standards Development Organization, to determine the TIC contrast 

performance. 

To perform the large area contrast test, the TIC is positioned 1 m from the test target. Figure 6—

5 illustrates how mirrors may be used to facilitate the measurement if space and/or alignment is a 

problem. For the data that was collected to support this work, a 17.8 cm square extended area 

blackbody was used as the radiation source. A 20.3 cm (8 in.) diameter gold-plated off-axis 

parabolic mirror having a focal length of 1 m and an offset angle of 10o

 was used to position the 

T2 surface within the field of view. All surfaces in the field of view except the mirror were 

painted with black paint, which has a stated ε = 0.94 ± 0.002 in the 8 μm to 14 μm wavelength 

range within which the fire service TIC operate. 

 
54

6.4. Effective temperature range (ETR) 

The ETR test is intended to measure the range of temperatures at which the TIC provides a 

useful image to the fire fighter. Useful means here that the image quality is adequate for the user 

to take appropriate action. It is not unusual for a fire fighter to use a TIC to search for objects 

having intermediate surface temperatures, for example a human victim, another fire fighter, or an 

egress route, when flames are in the field of view. In this situation, the presence of flames or 

other extreme conditions may cause the TIC to “wash out” or lose contrast in the object of 

interest. The ETR test measures the temperature range within which objects of intermediate 

temperature retain enough contrast to be discernable to the user, i.e., the temperature range of a 

useful image. A detailed discussion of the development of effective temperature range as it 

applies to fire service TIC can be found in [48]. 

The same test target is used for the ETR as for the large area contrast test, including the central 

area of the test target, in which bars of constant intermediate temperature are used to calculate 

the bar contrast. This test target, now showing the full complement of target areas, is shown in 

Figure 6—6. The bars in the test target had an outside diameter (OD) of 1.3 cm (0.5 in.) spaced 

1.3 cm apart, were constructed from copper tubing, producing a frequency of 0.04 cyc/mrad at a 

1 m distance from the TIC. For the bar contrast, Tbar is held constant at 30 °C ± 1 °C and Tsur is 

the background temperature. A constant temperature heating fluid (silicone oil) was pumped 

through the tubes to achieve a uniform test target temperature. As previously mentioned, the size 

of the T2 surface area must be large enough to cause the TIC under test to shift sensitivity mode, 

if the TIC is designed to shift mode, and the Tsur area has the same size as the T2 area. The Tbar

area is large enough to include at least 3 full bar cycles at 0.04 cyc/mrad. 

The contrast of the bars in the central area is calculated according to equation 1. The low 

temperature boundary of the ETR is held constant at 25 °C ± 1 °C and the high temperature 

boundary is Tmax, defining the ETR as shown below: 

ETR T Co = max − 25 , (2) 

The ETR is the temperature range to be established as the minimum acceptable operating 

temperature range for TIC. The bar contrast pass/fail criteria will be determined by the standards 

development organization. If during this test the TIC dips below the pass/fail value at any point 

in the test, then the corresponding T2 temperature is used in place of Tmax in equation 2 to 

calculate the ETR. If the TIC is designed to shift modes, then the T2 temperature corresponding 

with each mode shift is recorded as T2 moves through its range. 
55

Figure 6—4. Test target setup used for the contrast and effective temperature range tests. For 

large area contrast, the bars in the middle of the test target are ignored. The standard deviation of 

the combined pixel intensities within the dashed areas on the left and right side of the test target 

are calculated, then divided by the Bitdepth to determine the contrast as a function of T2, which 

changes from 25 °C to Tmax. 

Figure 6—5. Alternative test setup for contrast and effective temperature range. When space is 

an issue mirrors may be used to redirect the thermal radiation to the TIC. The results presented in 

this paper were obtained in this configuration. 

Tbar = 30 oC 

± 1 o

C 

Tsur = 25 oC, ± 1 oC 

(ambient) 

25 oC < T2 < Tmax

Hot Blackbody Cold Blackbody 

Bar Target 
56

Figure 6—6. This test target is used for the contrast and effective temperature range tests. For 

the effective temperature range, the contrast of the central area, which incorporates bars having a 

constant temperature difference, is measured while the hot blackbody surface temperature (T2) 

increases.

6.5. Nonuniformity 

Nonuniformity is a measure of the variation of the TIC’s response to a uniform test target. The 

uniform thermal test target used here is an extended area blackbody as shown in Figure 6—7. 

The TIC is placed close to the blackbody surface (~5cm) and the surface is assumed to be 

Lambertian, uniform irradiance in all directions, so that the TIC is interpreting a uniform 

temperature field. There are many ways that the TIC response may be nonuniform [49]: there 

can be gradients in pixel intensity across the image, various patterns such as narcissus may 

appear, some degree of broadband noise may be present, as well as blemishes and blotches, and 

combinations of these nonuniformities can occur. In Figure 6—8, images are presented from the 

same TIC, viewing a uniform target at four temperatures. As can be seen, as the test target 

temperature increased, nonuniformities in the images became generally more apparent. This TIC 

shifted to a less thermally sensitive mode between the 100 °C and 200 °C images. A detailed 

discussion of the development of nonuniformity as it applies to fire service TIC can be found in 

[50]. 

Tbar = 30 oC 

± 1 o

C 

Tsur = 25 oC, ± 1 oC 

(ambient) 

25 oC < T2 < Tmax

Hot Blackbody Cold Blackbody 

Bar Target 

Hot Oil In 

Hot Oil Out 
57

Nonuniformity is usually measured by entirely filling the field of view of the TIC under test with 

the blackbody surface set at a prescribed temperature. The image will not be in focus. The 

target is imaged and recorded, and the statistical mean, m, and standard deviation, σ, of the image 

pixel intensities are calculated. The nonuniformity, NU, is then given by the ratio of the standard 

deviation to the statistical mean, as shown in equation 3, which effectively makes the NU

independent of system gain [16]. 

NU

m

σ

= , (3) 

TIC have automatic nonuniformity corrections that are either continuously present or are 

triggered by various proprietary algorithms. Many sophisticated methods of correcting 

nonuniformity exist, however most fire service TIC utilize a linear correction to the offset of 

each pixel at ambient temperatures. As mentioned in section 2.2, TIC with BST-type detectors 

continuously correct the image by using a chopper to reset the detector’s nodes to uniform 

values. TIC with microbolometer detectors use a shutter to reset the pixels, which is triggered 

according to the manufacturer’s proprietary algorithm. During the shutter operation, which 

usually occurs in timed intervals, the displayed image freezes, therefore, for nonuniformity 

testing of TIC with microbolometers, it is important to time the data collection for this test such 

that it is free of automatic corrections. 

Figure 6—7. Test setup for measuring the nonuniformity of a TIC. The TIC is placed close to 

the surface (~5cm) of a uniform large area blackbody surface. The temperature is is increased 

and the images are taken by the visible camera to determine image nonuniformity.

 

Blackbody 

TIC

Visible Camera 
58

 30 °C 100 °C 

 200 °C 260 °C 

Figure 6—8. Variation in nonuniformity of a TIC with increasing temperature. As the test target 

temperature increased, nonuniformities became more apparent. The TIC shifted to a less 

thermally sensitive mode between the 100 °C and 200 °C images. 

As seen in Figure 6—8, image nonuniformity is sensitive to the test target temperature, therefore 

it is measured at several critical temperatures: water freezing temperature, 1°C, human body 

temperature, 30°C, water boiling temperature, 100°C, and two temperatures at which other fire 

service equipment such as turnout gear is tested, 200°C and 260°C respectively. Tests have not 

been performed at 1 °C at this time. Small values of NU are desired for this test, therefore the 

nonuniformity is determined at all these test target temperatures and compared with the 

maximum pass/fail criteria determined by the standards development organization to characterize 

the TIC contrast performance. Nonuniformity also plays a role in the determination of the TIC’s 

spatial resolution, as discussed in the following section. 
59

6.6. Spatial resolution 

Spatial resolution is a measure of the amount of detail in an image. A fire fighter may observe a 

hotspot, noticeable by a difference in contrast, but not realize that the source is a warm but 

harmless household item (e.g., a computer, coffee pot, power strip, lamp, etc...). Without 

enough detail in the image to identify the item of interest, the fire fighter may lose valuable time 

inspecting everything that looks relatively warm. A detailed discussion of the development of 

spatial resolution as it applies to fire service TIC can be found in [51]. 

There are numerous ways to measure spatial resolution, most of which are discussed in [51]. 

The slanted edge Modulation Transfer Function (MTF) measurement was chosen for this test 

because it has high repeatability and is relatively easy to perform. An existing test method for 

visible cameras, ISO 12233 [28], was used as the basis for this test, with modifications related to 

the thermal target. The test target is configured as shown in Figure 6—9. The slant is 5° from 

vertical and the hot, cold, and surrounding temperatures are held constant throughout the test. 

The 5° angle avoids aliasing by not aligning with the camera pixels and facilitates oversampling 

of the edge by four times to get a more accurate representation of the gradient and resultant 

frequency response. The test target dimensions are at least 15 cm in each direction. For the data 

that was collected to support this work, a 17.8 cm square extended area blackbody was used as 

the heat source and a thin sheet of aluminum, coated with black paint having ε = 0.94 ± 0.002 

and cut at the appropriate angle, was placed directly in front of the blackbody surface. 

Spatial resolution is independent of the test target temperatures, so long as the steady (nongradient) temperatures on either side of the test target produce at least a 20 % pixel intensity 

difference in the images generated by the TIC. The TIC is positioned 1 m away from the target. 

The image data are captured, then processed using software based on the ISO 12233 test method 

[52], resulting in a curve of MTF as a function of frequency, which is normalized to a value of 1 

at zero frequency. The process of determining the MTF function includes combining 4 lines of 

the image together to effectively oversample the edge four times. Then the edge is differentiated 

to produce a line. A Fourier transform of the line is taken and the data points are taken as the 

maximum amplitude of each frequency derived from the image. Finally the MTF function is 

normalized to the zero frequency MTF response. This method provides a purely relativeistic 

measurement of the frequency response which only has quantitative value once the MTF is 

normalized to the zero frequency. This has the added benefit of producing a measurement 

method that is independent of target temperature, as long as a sufficient temperature difference is 

present for the camera to respond to. A sample MTF curve is given in Figure 6—10. The 
60

Figure 6—9 Slanted edge spatial resolution test target. The slant is 5 o from vertical, the hot 

and surrounding temperatures are held constant throughout the test. The target dimensions are at 

least 15 cm in each direction. All surfaces in the field of view have ε ≥ 0.94 ±0.002. 

nonuniformity value obtained at 100 °C from the test method described in section 6.5 is 

considered the “noise floor,” wherein the measured MTF is due to contrast variations caused by 

the noise in the signal rather than the test target’s contrast. The noise floor can vary significantly 

among TIC, therefore it is important to compensate by removing it from the spatial resolution 

calculation. 

As the frequency increases, the MTF flattens because the fluctuations in the noise inherent in any 

image approximate the length scale of the image frequency. The spatial resolution is obtained by 

integrating the area between the curve and the noise floor shown in Figure 6—10. 

The spatial resolution obtained in this test method is compared with the minimum pass/fail 

criteria determined by the standards development organization to determine the TIC spatial 

resolution performance. 

Tsur = 30 oC 

(all temperatures ± 1 o

C) 

T1 = 25 o

C 

constant

T2 = 100 oC 

constant

Blackbody 

Room temperature 

slanted edge target. 
61

Figure 6—10 Sample spatial resolution data. The spatial resolution is obtained by integrating 

between the MTF (red line) and the nonuniformity (blue line). 

6.7. Thermal Sensitivity 

The thermal sensitivity test measures the smallest temperature difference that the TIC is capable 

of resolving. The sensitivity of most TIC to temperature differences is a function of the nominal 

scene target temperature, therefore this test is performed at the same critical temperatures 

identified previously in the discussion of nonuniformity in section 6.5. These temperatures are 

1 °C, 30 °C, 100 °C, 160 °C, and 260 °C. 

To measure thermal sensitivity, two extended area blackbodies are placed in the TIC field of 

view such that they each show an equal area in the displayed image as seen in Figure 6—11. 

The blackbodies do not need to be in focus. One blackbody is set at a prescribed temperature 

and the other blackbody set point is adjusted until the luminance of both areas in the displayed 

image is equal. The adjusted blackbody set point is then incrementally increased until the 

luminance value increases by 2 %; this temperature is recorded as T1. The blackbody set point is 

then incrementally decreased until the luminance value decreases by 2 %; this temperature is 

recorded as T0. The thermal sensitivity (TS) is calculated by equation 4. 

2

T1 T0 TS − = , (4) 

TS measurements are determined at all five of the test target temperatures. Small values of 

thermal sensitivity are desired for this test. The test results are compared with the maximum 

pass/fail criteria determined by the standards development organizations to determine the TIC 

contrast performance. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.05 0.1 0.15 0.2 0.25

MTF

Frequency (cyc/mrad)

Noise floor 

(nonuniformity) 

SFR 
62

Figure 6—11. Experimental setup for thermal sensitivity test. The two blackbodies are adjusted 

until they both have the same luminance on the TIC display. Then one blackbody temperature is 

slowly decreased until a 2 % difference in luminance is observed between the two blackbodies.

Blackbody adjusted 

from T1 to T0 

Constant Temperature 

Blackbody 
63

7. RESULTS AND DISCUSSION 

In this section, examples are given of test data collected during the development of the test 

methods discussed in section 6. They are intended to illustrate the differences between TIC and 

to clarify the intention of the tests. The TIC are differentiated by their detector technology 

because it is an easy and obvious way to compare TIC performance. It should be emphasized 

that detector technology alone does not determine the relative performance of TIC. The size of 

the detector array, the electronic processing, the optical system, and the quality of the display 

play very important roles in TIC performance but are not directly useful to differentiate 

performance. 

7.1. Contrast and ETR 

In this discussion the TIC are differentiated by their detector technology because it is an easy and 

obvious way to compare TIC performance. It should be emphasized that detector technology 

alone does not determine the relative performance of TIC. The size of the detector array, the 

electronic processing, the optical system, and the quality of the display play very important roles 

in TIC performance but are not directly usable to differentiate performance. 

The large area contrast and the bar contrast are plotted in 

Figure 7—1 to Figure 7—3 as a function of T2 temperature; there are two tests shown in each 

graph. T2 is the temperature of a surface of area large enough to cause the TIC under test to shift 
64

sensitivity mode (if the TIC is designed to shift mode). In 

Figure 7—1, the ASi TIC did not provide a stable image until the T2 temperature reached about 

125 °C. Below 125 °C, the large area contrast instability manifested itself as flickering between 

brighter and darker images. Above 125 °C, the image stabilized until the TIC shifted mode, 

which occurred at around 290 °C. After the mode shift, the fluctuations in large area contrast 

were larger than at lower T2 temperatures. This behavior occurred in both tests and appears to 

be a characteristic of the specific TIC tested. The bar contrast was unaffected by the fluctuations 

of the hot pixels but degraded significantly after the TIC shifted mode. After the mode shift both 

the large area and bar contrasts were more unstable than at lower T2 temperatures. 

In Figure 7—2, the BST TIC presented very different results, with the large area contrast 

improving dramatically with the initial increase in T2 temperature. The maximum large area 

contrast was achieved at T2 = 170 °C, although the contrast for this TIC was generally lower than 

either of the other TIC. Recall that BST detectors do not shift modes. The bar contrast became 

quite low after the initial increase in T2 temperature and stayed low throughout the remainder of 

the test. 

Similar to the BST TIC, in Figure 7—3 it can be seen that the VOx TIC large area contrast also 

improved greatly with the initial increase in T2 temperature. Unlike the ASi TIC, the VOx TIC 

large area contrast did not suffer noticeably after the mode shift, remaining consistently higher 

than the other two TIC throughout the tests. There were a few brief but significant contrast 

excursions that occurred during several of the TIC’s automatic nonuniformity corrections. The 

bar contrast declined somewhat during the period prior to the mode shift. After the mode shift 

the bar contrast became quite low and stayed low throughout the remainder of the test. 

The bar contrast is used to determine the TIC’s ETR. As mentioned previously, the minimum 

acceptable bar contrast and the minimum ETR will be established by the standards devlopment 
65

organization. For the sake of discussion, assume that the minimum bar contrast has been 

arbitrarily set at 0.2. In Figure 7—1, the ASi TIC shows an ETR of about 265 °C (290 °C – 

25 °C), in Figure 7-2 the BST TIC shows an ETR of about 15 °C (40 °C – 25 °C), and in Figure 

7-3 the VOx TIC shows an ETR of about 125 °C (150 °C – 25 °C). Note that the bar contrast 

value of 0.2 was chosen for this discussion strictly to illustrate the differences in TIC 

performance and how they might relate to a pass/fail criterion and is not intended to indicate a 

preference for any specific value. These results indicate the wide range in image performance. 

 

Figure 7—1. Plots of large area contrast and bar contrast data used to determine image contrast 

and effective temperature range of a TIC using an ASi, 120 x 160 detector array. Test results for 

two tests are shown.

T2 
66

Figure 7—2. Plots of large area contrast and bar contrast data used to determine image contrast 

and effective temperature range of a TIC using an BST, 240 x 320 detector array. Test results 

for two tests are shown.

Figure 7—3. Plots of large area contrast and bar contrast data used to determine image contrast 

and effective temperature range of a TIC using an VOx, 120 x 160 detector array. Test results 

for two tests are shown.
67

7.2. Nonuniformity 

The nonuniformity of three TIC is displayed for several temperatures in Figure 7—4 and the 

nonuniformity values are plotted as a function of target temperature in Figure 7—5. It can be 

seen that nonuniformity generally increases with increasing target temperature, although a 

discontinuity may occur when the TIC shifts sensitivity mode. Note that the BST TIC showed a 

monotonically increasing nonuniformity. For the three specific TIC tested, the VOx TIC 

produced the least amount of nonuniformity (provided the most uniform images). When the 

sensitivity of the systems decreased due to the mode shift, there was a corresponding decrease in 

nonuniformity. This suggests that the nonuniformity scaled with temperature, but on a 

fundamental level it actually scaled with pixel saturation. The BST TIC was more sensitive to 

target temperature than the other two TIC. 

Several different examples of nonuniformities can be observed in Figure 7—4. The BST camera 

at 100 °C exhibits a narcissus effect which can be seen as the faint circle in the center of the 

image. Narcissus is when internal reflections occur in the camera causing it to see its own optics. 

As the temperature increases for the BST camera more drastic nonuniformities become apparent 

in the form of diagonal shading of the image. This is partially due to the design of the BST 

camera and its use of a chopper. The chopper is still at room temperature while the camera is 

observing a high temperature input. The effect is a continuous switching between high 

temperature uniform input and low temperature uniform input and presents as the diagonal 

shading seen at 200 °C and 260 °C. 

The ASi images shown in Figure 7—4 present several additional types of nonuniformity. At 

100 °C, prior to the mode shift, the camera exhibits some pixel saturation near the bottom of the 

image. This is a good illustration of the need for a mode shift and how that reduced sensitivity 

mode affects the image presented by the camera. The pixel saturation is gone at 200 °C because 

of this mode shift. Another type of nonuniformity that can be seen for the ASi camera is the 

presence of physical defects in the camera as evidenced by the dark and light circles on the 

image which can be seen at elevated temperatures. 

All of these different nonuniformities can affect camera output differently, and if localized may 

not significantly impact the gross image. However, all the nonuniformities are treated 

numerically as broadband noise in the image. Additionally, nonuniformity impacts the spatial 

resolution of the camera as well. If the amplitude and frequency of noise is at the same spatial 

frequency of some detail in a scene that is being imaged then that detail will be lost in the noise 

and not be detected. For this reason the nonuniformity of each camera is used as a ‘noise floor’ 

in the spatial resolution measurements. The camera is assumed to be unable to discern detail that 

is in the noise. The implementation of nonuniformity to the spatial resolution calculation is 

discussed in section 7.3. 

 
68

30°C 100°C 200°C 260°C 

BST 

VOx 

ASi 

BST 

VOx 

ASi 

BST 

VOx 

ASi 

BST 

VOx 

ASi 

Figure 7—4. Actual nonuniformities observed from three different TIC at a variety of 

temperatures. BST, VOx, and ASi detector technologies are all represented along with a variety 

of different nonuniformities present in these cameras. 

Figure 7—5. Image nonuniformity as a function of target temperature while looking at a 

uniform temperature surface. For the three specific TIC tested, the VOx TIC produced the least 

nonuniformity while the ASi and BST cameras had higher nonuniformities at different 

temperatures.

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150 200 250 300

Temperature (◦

C)

NU

BST

VOx

ASi

Mode Shift 
69

7.3. Spatial resolution 

The spatial resolution of a TIC is representative of how well that TIC can see detail. Since the 

methodology is built upon the ISO 12233 standard for determining the spatial resolution of 

visible spectrum cameras a similar figure of merit is used here, namely the Spatial Frequency 

Response (SFR). Based on the discussion in Section 6.6, the SFR is a nondimentional number 

that varies from 0 to 1 and a larger value indicates a better representation of spatial detail in an 

image. Figure 7—6 illustrates how a perfect knife edge is interpreted by three different cameras. 

As mentioned earlier, the spatial resolution of each TIC is dependent on the camera’s optics, 

internal image processing, and display screen in addition to the physical pixel resolution of the 

internal sensor. This can be clearly seen in Figure 7—6. The actual MTF curves (see Section 6.6) 

calculated from these slanted edge images are presented in Figure 7—7. 

The contrast of the image does not affect the spatial resolution measurment of the camera. The 

ASi camera appears to have a much higher image contrast than the VOx, however when you 

look at the actual measured SFR value, the VOx camera has a larger SFR value than the ASi 

camera. This may seem counterintuitive, and if the MTF values are not normalize to the zero 

frequency there is infact a significant effect of contrast (or target temperature differential) on the 

SFR value obtained. Figure 7—8 presents three MTF curves taken from the same camera at 

different temperatures. Without normalization the SFR appears to improve significantly as the 

temperature, or contrast, of the scene increases. However, once the values are normalize, as seen 

in the right of Figure 7—8, they all collaps together and return essentially the same result. This is 

important to take into account for spatial resoultion since contrast is measured separately. There 

is however a need to have a minimum contrast for the measurement to work. Observing the 40 

°C curve in the normalized plot of Figure 7—8, errantly high MTF are reported at higher 

frequencies while identical, low values are observed for 80 °C and 100 °C. 
70

 

100°C/30°C BST 

100°C/30°C VOx 

100°C/30°C ASi 

Figure 7—6. Illustration of how of how three different cameras interpret the same ‘knife edge’ 

thermal target. The three different cameras have different sensor technology, but also have 

different pixel resolutions (320x240, 160x120, and 160x120 respectively), optics, and internal 

image processing that affects the spatial resolution of the image on the display. The analysis of 

these images is presented in Figure 7-6.

 
71

BST Camera 

SFR ≈ 0.37 

VOx Camera 

SFR ≈ 0.30 

ASi Camera 

SFR ≈ 0.17 

Figure 7—7. Comparison of the spatial resolution of the BST, VOx, and ASi TIC. The SFR 

value given for each camera technology represents the area between the MTF curve and 

Nonuniformity. The spatial resolution measurement for each camera is dependent upon the 

nonuniformity measurement as well. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.05 0.1 0.15 0.2 0.25

MTF

cyc/mrad

0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15 0.2 0.25

MTF

cyc/mrad

0

0.2

0.4

0.6

0.8

1

1.2

0 0.05 0.1 0.15 0.2 0.25

MTF

cyc/mrad
72

 

Figure 7—8. Illustration of the temperature independence of the spatial resolution measurement. 

The temperatures are indicated in Celsius. Once the original values (top) are normalized (bottom) 

the effect of image contrast (temperature difference) can be eliminated. The line for 40 °C on the 

right does not follow the other trends because there needs to be a minimum contrast in the knife 

edge image.

7.4. Thermal sensitivity 

As discussed earlier, thermal sensitivity is the ability of the camera to convey small changes in 

temperature to the users. As discussed in section 6.7 two blackbodies are used and the 

temperatures are initially set so that the intensities measured on the display, by the visible camera 

are equal, and then varied until a 2 % difference in measured pixel intensity is measured. The test 

is repeated at several different temperatures in each of the temperature classes. Only data for a 

single TIC was available at the time of this writing. More test data will be available in the near 

future, however, it is not available. Figure 7—9 presents a sample thermal sensitivity curve for a 

VOx TIC. When a TIC has a smaller the thermal sensitivity value then the better the camera 

performs as the smaller temperature difference it can percieve. As the nominal temperature, T1, 

increases a larger temperature difference is necessary to produce sufficient contrast for the user 

to percieve. Additionaly, when some cameras ‘mode shift’ at higher temperatures this decreses 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.00 0.10 0.20 0.30

MTF

cyc/mrad

40C

60C

80C

0

0.2

0.4

0.6

0.8

1

1.2

0.00 0.10 0.20 0.30

MTF

cyc/mrad

40C

60C

80C
73

the sensitivity of the detector resulting in a necessarily larger temperature difference to be 

present in order for the camera to respond. No mode shift is observed in Figure 7—9. 

The pass/fail critera for the thermal sensitivity of a TIC will be determined by the standards 

development organizaition that is creating the standard. 

Figure 7—9. Example thermal sensitvity response for a characteristic TIC. A smaller value for 

thermal sensitivity indicates that the camera is more sensitive to small differences in temperature. 

The thermal sensitivity increases with increasing nominal temperature due to a larger contrast 

necessary for the user to percieve a temperature difference.

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200

TS

Nominal Test Temperature, T1 (°C)
74

7.5. Uncertainty Analysis 

There are different components of uncertainty in the temperatures, total heat flux, and time to 

activate data reported here. Uncertainties are grouped into two categories according to the 

method used to estimate them. Type A uncertainties are evaluated by statistical methods and type 

B are evaluated by other means [53]. 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 percent. 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 total expanded uncertainty that corresponds 

to a 95 percent confidence interval (2σ). 

Components of uncertainty are tabulated in Table 7-1 and Table 7-2. Some of these components, 

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

components, such as path length and image digitization include past experience with positioning 

these devices and the image digitization equipment used. The uncertainty in the air temperature 

measurements does not include radiative cooling because of the relatively low temperatures 

being measured. Smoke density measurements were conducted gravimetrically. Part of the 

uncertainty was attributed to the accuracy of the mass scale used to weigh the soot filters and 

part of the uncertainty was due to the flow rate which is measured after the gases have been 

cooled and is therefore highly depended on the temperature at the entrance to the soot probe. The 

contrast transfer function (CTF) measurements involved looking down a long corridor. There can 

be significant variations in the composition and temperature of the gases in this length. The 

uncertainty also varies with the amount of smoke loading and turbulent flow in the corridor. The 

uncertainties are reported as a range in Table 7-1 and are represented by error bars in the 

associated figures. 

The bench scale experiments are by their very nature more controlled and thus expected to have 

smaller uncertainties associated with them. The blackbodies used in these experiments are very 

well controlled devices and generally have a small uncertainty associated with their temperature 

set point and an even smaller uncertainty associated with their temperature steadiness. Due to the 

wide variations in the TIC form factors it is very difficult to position each camera so that the lens 

is in the same position for each of these tests, this results in a positioning uncertainty mostly 

manifested by variations in the path length. For the Nonuniformity test the uniformity of the 

blackbody surface is very important. The blackbody used in these experiments had its uniformity 

quantitatively measured by the Physics Laboratory at NIST. The resultant uncertainty in the 

blackbody surface is much smaller than that being measured by the test and is represented in 

Table 7-2. As with the full scale tests there is a small uncertainty associated with converting the 

analogue image signal to a digital format for processing, this uncertainty is represented in both 

Table 7-1 and Table 7-2 

.
75

Table 7-1: Uncertainty in full scale experimental test data.

Component 

Standard 

 Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

CO concentration 

 Calibration 

 Repeatability 

 Random 

±1% 

±4% 

±3% 

±5% ±10% 

Temperatures 

 Calibration 

 Repeatability 

 Random 

±1% 

±1% 

±1% 

±1.5% ±3% 

Smoke Density 

 Mass Scale 

 Flow Rate 

±2% 

±5% 

±5% ±10% 

Contrast Transfer Function (CTF)*

 Path Length Uniformity 

 Random 

±2% to ±50% 

±2% 

±2.5% to ±50% ±5% to ±100% 

* Variations in uncertainty are plotted as error bars in the respective figures. 

Table 7-2: Uncertainty in bench scale experimental data. 

Component 

Standard 

 Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

Contrast 

 Temperatures 

 Image Digitization 

 Path Length 

±1% 

±2% 

±5% 

±5% ±10% 

Nonuniformity 

 Temperature of Blackbody 

 Blackbody Uniformity 

 Repeatability 

 Image Digitization 

±1% 

±0.5% 

±3% 

±2% 

±3.5% ±7% 

Spatial Frequency Response 

 Path Length 

 Image Digitization 

±5% 

±2% 

±5% ±10% 

 
76

8. SUMMARY 

For thermal imaging cameras that will be used by the fire service, this study has identified the 

needs and issues involving the image performance of thermal imaging cameras. In this study, 

relevant information regarding the establishment of conditions under which to test the 

performance of TIC has been assembled with the objective of developing test conditions that are 

relevant and representative of fire service operations. Input from users, as well as existing 

standards, research reports, and test measurements were considered in the development of 

representative TIC performance testing conditions. The concept of Thermal Class as a means of 

categorizing the activities in which TIC are used by fire fighters is helpful in defining 

meaningful bounds on TIC test conditions. The four thermal classes link the various 

requirements of existing standards on related fire service equipment with experimental results 

from full-scale testing and the scientific literature. 

This report presents the suite of imaging performance metrics and test methods that were 

developed to aid in the creation of a standard on thermal imagers used by the fire service. The 

performance metrics and test methods reflect the need of fire service TIC images to have 

sufficient contrast, temperature range, spatial resolution, and thermal sensitivity, along with 

reduced nonuniformity to facilitate effective TIC use. 

Data collected during the development of these tests provides an indication of the wide range of 

imaging performance produced by TIC currently being used by the fire service. There was no 

particular TIC detector technology or model that excelled in every test. In fact, the test results 

show that each TIC technology tested was superior to the others in at least one test. 

The standards development organizations will determine pass/fail criteria for each of the 

individual tests. In the future, data regarding the ability of users to perceive hazards with various 

types and quantities of image degradation will be provided to the standards development 

organizations. There may be interactions between the various image parameters. The standards 

development organization will determine, based on the the magnitude and degree of these 

interactions, whether they should be considered in the final pass/fail criteria. 

 
77

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81

APPENDIX A 

This appendix lists the performance metrics and test methods that may be incorporated into 

standards for thermal imaging cameras. The following performance metrics and test methods are 

presented in a generalized form designed to give the reader a sense of the scope of a standard. 

The Technical Committee responsible for a standard makes decisions regarding the content of 

the standard on a consensus basis. Before the final form of a standard document is published, 

draft versions of the document are offered to the public for proposed changes in scope and for 

revisions to text. At the discretion of the committee, all or part of the recommendations such as 

the ones provided in this report may or may not be included in the final standard document. 

The performance metrics and test methods are divided into two groups, the first being listed in 

Table A-1. This group addresses the overall design robustness of the thermal imaging camera 

design. When appropriate, existing standard test methods are used. In other cases, when 

existing tests were not appropriate or were deemed inadequate, new test methods were developed 

specifically for first responder thermal imaging cameras. 

Table A-1. Design Robustness Performance Metrics and Test Methods

Performance Metric Test Method 

Nonincendive Equipment ANSI 12.12.01 

Enclosure Protection IP67 

Electromagnetic Emission IEC 61000-6-3 

Electromagnetic Immunity IEC 61000-6-2 

Temperature Stress Environmental Temperature Stress Test 

Leakage Resistance Immersion / Leakage Test 

Vibration Resistance Vibration Test 

Impact Resistance Impact-Acceleration Resistance Test 

Corrosion Resistance Corrosion Test 

Heat Resistance Heat Resistance Test 

Flame Resistance Heat and Flame Test 

Tumble “Torture” Resistance Tumble-Torture Test 

Viewing Surface Abrasion Resistance Viewing Surface Abrasion Test 

Product Label Durability Product Label Durability 

Wire Pullout Resistance Cable Pullout Test 
82

The imaging performance of the thermal imaging camera is addressed by a second group of 

performance metrics and test methods, as listed in Table A-2. This group is the primary focus of 

the work conducted for this project and is discussed in greater detail in sections 6 and 7. 

Table A-2. Imaging Performance Metrics and Test Methods

Performance Metric Test Method 

Contrast 

Contrast Test- determines the maximum possible 

contrast that can be displayed by the thermal imaging 

camera. 

Effective Temperature Range 

Effective Temperature Range Test- determines the 

extreme range of temperatures (which control the 

camera’s automatic gain settings) that allow the user to 

see an intermediate-temperature target. 

Image Uniformity 

Uniformity Test- measures the thermal imaging 

camera’s ability to produce a perfectly uniform image. 

This test is performed at several different temperatures. 

Spatial Resolution Spatial Resolution Test- determines the level of detail 

that can be displayed by the thermal imaging camera. 

Thermal Sensitivity 

Thermal Sensitivity Test- determines the smallest 

measurable temperature difference indicated on the 

display screen. This test is performed at several 

different temperatures. 

A draft standard may also include a “Image Recognition Test”, which is intended to act as a 

pass/fail criterion for some of the robustness test methods. For example, after a camera is tested 

for heat and flame resistance, the Image Recognition Test will be conducted to determine 

whether the camera’s image quality has been degraded. 
83

APPENDIX B 

Table B-1 lists existing standards that may have bearing on TIC operating conditions for 

functional and image quality tests. 

Table B-1. Standards relating to TIC operating conditions and test methods

ASTM E 1213-97 

Standard Test Method for Minimum Resolvable Temperature Difference for 

Thermal Imaging Systems – Test uses a trained observer, target near ambient 

temperatures.

ASTM E 1256-95 Standard Test Methods for Radiation Thermometers (Single Waveband Type) – 

used for measuring the temperature of a blackbody. 

ASTM E 1311-89 

Standard Test Method for Minimum Detectable Temperature Difference for 

Thermal Imaging Systems – Test uses a trained observer to determine thermal 

sensitivity near ambient temperatures. 

ASTM E 1543-00 

Standard Test Method for Noise Equivalent Temperature Difference of Thermal 

Imaging Systems – measures thermal sensitivity objectively, at ambient 

temperatures. 

ASTM E 1862-97 

Standard Test Methods for Measuring and Compensating for Reflected 

Temperature Using Infrared Imaging Radiometers – used for surface temperature 

measurements. 

ASTM E 1897-97 

Standard Test Methods for Measuring and Compensating for Transmittance of an 

Attenuating Medium Using Infrared Imaging Radiometers – used when 

measuring through obstructing media. 

ASTM E 1933-

99a 

Standard Test Methods for Measuring and Compensating for Emissivity Using 

Infrared Imaging Radiometers - used for surface temperature measurements. 

BS EN 60529 Enclosure protection rating system, IP 67 for water and dust ingress 

BS EN 50081-

2:1991 EMC emission 

BS EN 50082-

2:1992 EMC immunity 

MIL-STD 810E Method 513.4, Acceleration 

NFPA 1221 Standard for Installation, Maintenance and Use of Emergency Services Communications 

Systems

Section 8.3.5.4 

“Mobile radios and associated equipment shall be manufactured for the 

environment in which they are to be used.” No mention of specific testing 

criteria. 

Section 8.3.6.2 

“Portable radios shall be manufactured for the environment in which they will be 

used and shall be of a size and construction to allow their operation with the use 

of one hand.” No mention of specific testing criteria. 

NFPA 1971 Standard on Protective Ensemble for Structural Firefighting

Section 6.6 No igniting, melting, dripping, or separating of garments tested at 260 °C for 5 

min. 

Section 6.9 Footwear must withstand 10 kW/m2

 for 1 min 

Section 6.10 Flashover conditions for gloves, hoods, wristlets, and multiplayer protective 

garment composites must withstand 83 kW/m2

 for 30 s. 

Table continued on next page. 
84

 

Table B-1 continued... 

NFPA 1977 Standard on Protective Clothing and Equipment for Wildland Firefighting

Section 6.2 Radiant protective test for garment and face/neck shroud, tested at 21 kW/m2

 for 

30 s. 

Section 6.4 Heat and thermal shrinking resistance test, garment and face/neck shroud tested at 

260 o

C for 5 min. Helmets are tested at 177 oC for 5 min. 

Section 6.14 Glove heat resistance tested at 204 o

C for 5 min. 

Section 6.22 Gloves materials are exposed to 83 kW/m2 for 30 s. 

NFPA 1981 Standard on Open-Circuit Self-Contained Breathing Apparatus for Fire and Emergency 

Services

Section 8.2 Cold soak- test for air flow performance, cycles cold/hot and hot/cold, -32 o

C to 

71o

C 

Section 8.5 Fabric components of SCBA are tested at 260 o

C for 30 min. 

NFPA 1982 Standard on Personal Alert Safety Systems

Section 6.2 

Electronic temperature stress test cycles PASS device through temperature 

fluctuations of 49 o

C to 71 oC at 360 min/ 240 min cycles. (Test procedure 1) 

PASS device is cycled through temperature fluctuations of -20 oC to 71 oC at 240 

min. cycles. (Test procedure 3) 

Section 6.11 Heat resistance test, device exposed to 260 o

C for 5 min. 

NFPA 1800 Standard on Electronic Safety Equipment for Emergency Services

UL 913 Standard on Intrinsic Safety 

VESA Flat Panel Display Measurements Standards, Version 2.0 
85

INDEX 

AC-Coupling ............................................. 17 

Aliasing ..................................................... 59 

ANSI ......................................................... 23 

ASTM ....................................................... 23 

Barium Strontium Titanate (BST)15, 17, 18, 

37, 57 

Bitdepth ..................................................... 53 

Black Body................................................ 13 

Charge Coupled Device (CCD) ................ 17 

Chopper ..................................................... 17 

Compartment Fires.............................. 24, 25 

Contrast ............................................... 52, 63 

Contrast Transfer Function (CTF) 30, 37, 73 

Hose Stream .......................................... 47 

DC-Coupling ............................................. 17 

Effective Temperature Range (ETR)50, 54, 

63 

Emissive Paint ............................... 28, 31, 53 

Field of View (FOV) ..................... 19, 27, 47 

Fire Dynamics Simulator (FDS) ............... 34 

Fire Environment .......................... 19, 24, 25 

Focal Plane Array (FPA) .......................... 15 

Fourier Transform ..................................... 59 

Fourier Transform Infrared Spectrometer 

(FTIR) ....................................... 30, 33, 43 

Gas Analyzers, O2, CO, CO2 .................... 31 

Heat Release Rate ..................................... 27 

Heat Release Rates .................................... 30 

Hose Stream .................................. 34, 35, 44 

Image Quality............................................ 36 

Image Recognition Procedure (IRP) ......... 50 

International Organization for 

Standardization (ISO) ........................... 23 

ISO 12233 ....................................... 50, 59 

Intervening Media ..................................... 36 

Large Fire Laboratory ............................... 28 

Microbolometers ............... 17, 18, 37, 39, 57 

ASi ............................................ 15, 17, 39 

VOx ........................................... 15, 17, 38 

Mode Shift .......................................... 53, 54 

Modulation Transfer Function (MTF) ...... 59 

Navy Testing ............................................. 19 

NFPA ........................................................ 23 

Noise Floor................................................ 60 

Nonuniformity..................................... 56, 66 

Definition .............................................. 57 

Performance Metrics ........................... 20, 50 

RADCAL .................................................. 14 

Robustness Test ........................................ 51 

SAFE-IR ................................................... 22 

Sight Distance ............................... 37, 40, 42 

Smoke/Soot ....................... 24, 27, 30, 31, 41 

Spatial Resolution ............................... 59, 68 

Temperature Dependence of Spatial 

Resolution ............................................. 68 

Thermal Classes .................................. 23, 50 

Thermal Imaging Cameras (TIC) 

Design Componenets ............................ 17 

Image Performance ......................... 19, 20 

Image Quality........................................ 15 

Imaging Performance ............................ 40 

Physical Robustness .............................. 19 

Positioning ............................................ 32 

Settings .................................................. 15 

Target .................................. 28, 29, 31, 32 

Training ................................................. 22 

Uses ............................... 19, 20, 26, 27, 49 

Thermal Radiation .................................... 13 

Thermal Sensitivity ................................... 61 

Thermocouples .................................... 28, 31 

Thermoelectric Cooler (TEC) ................... 17 

UL ............................................................. 23 

Uncertainty ................................................ 73 

Emissive Paint ....................................... 53 

Hose Stream CTF .................................. 47 

VESA ........................................................ 23 

Victm, Simulated ...................................... 31 

Visible Camera .......................................... 52