Thermal imaging is one of the fastest growing technological industries. The past six years have seen numerous companies manufacture thermal imagers for the fire service. In a heavy smoke condition, firefighters are without vision. Thermal imagers can help restore their lost vision. With technology growing at a faster pace than ever before, these units can be manufactured so that they are small enough to use, easy to maintain, and low in cost.

Thermal imaging units can dramatically increase firefighter safety when used properly by a trained operator. Therefore, the question is not whether fire departments should purchase thermal imaging units, but what criteria should be used to make the right purchase. The problem is that very little information is available to the personnel who must make the decision.


Some departments do take the time to evaluate the units, at times even in a burn building or possibly an acquired structure, yet this still may provide only subjective information, since the personnel performing the evaluation have little if any training in thermal imaging or in how to apply this knowledge to the fireground. The test should be kept as objective as possible. Often the testing consists of a few chosen firefighters’ entering the burn building with each unit to be evaluated and then being asked, “Which one did you like?” This type of test is purely subjective. Fire departments are only cheating themselves and the manufacturers by performing this type of test.


One single factor cannot determine which thermal imaging unit will best suit a department’s needs. When evaluating thermal imaging units, all units should be evaluated under the same conditions. Fires are very dynamic, so if you take one unit into a burn building to evaluate the image and then return later with a different unit, unless someone maintained the conditions, the next unit will not give the same picture. In fact, the first unit would not, or at least should not, give the same picture because conditions are different.

Departments should consider at least the following factors when purchasing a thermal imaging unit. They will help make the evaluation as objective as possible.

  • Sensitivity. This can be determined by finding out from each manufacturer the Minimum Resolvable Temperature Difference (MRTD)-a measure of how little heat the unit can distinguish. The lower the unit’s MRTD, the more sensitive the unit. As an example, a unit with an MRTD of 10%deg;C would be twice as sensitive as a unit with an MRTD of 20°C. Firefighters often misunderstand this during sales presentations. The MRTD of a thermal imaging unit is critical from an electronics standpoint. Just because a thermal imaging unit may be able to distinguish among temperatures as low as .5°F, or even lower, that does not mean that the operator will be able to distinguish this small a temperature difference simply by looking at the image. However, it is important for the user in the picture clarity of a cold scene. This sensitivity also aids the user in distinguishing a heat source in a cold scene.

Some units may offer the ability to see in color. This does not mean that the colors will distinguish temperature difference. Some manufacturers may list this information (MRTD) in Fahrenheit rather than Centigrade. You should convert all of the information from the manufacturers to the same units of measure. This information can be easily converted using the proper formula.

To convert Centigrade to Fahrenheit, use the following formula:

°C(9/5) + 32 = °F.

To convert Fahrenheit to Centigrade, use the following formula:

(°F – 32) 5/9 = °C.

Once this is done, firefighters should make an evaluation in both a heated, controlled live-fire situation and in an unheated cold scene. This should allow the operators to view the image under simulated realistic conditions.

  • Clarity. The clarity the unit offers will be dependent on several factors. The first is the MRTD of the unit. The lower the MRTD of the thermal imaging unit, the better the clarity the unit will provide. The quality of electronics used to display the image will also have an effect. (The electronics of the unit is beyond the scope of this article.) However, this is not the only factor. As stated earlier, thermal imaging units must be tested under similar conditions. A unit evaluated in a cold scene will not seem to have the same clarity as a unit evaluated in a hot scene, although in fact it may.
  • Range. The range of the thermal imaging unit is also related to the unit’s MRTD. However, several other factors will affect the range of a thermal imaging unit. Weather conditions such as rain, fog, and snow may greatly affect the range at which the thermal imaging unit will detect a heat source. The heat source itself will also dramatically affect the range of the thermal imaging unit. Once again, all the thermal imaging units should be evaluated under the same conditions.
  • Field of view (FOV). All thermal imaging units give the operator tunnel vision to some extent. Some units, however, have a wider field of view than others. The wider the field of view, the more the operator will see of the scene. A slightly narrow field of view is not necessarily a poor quality, provided that the firefighter is trained in how to properly use the unit on the fireground.
  • Size. The size of the unit will have some effect on the ease with which the unit can be operated on the fireground. However, this is not a large problem with most of today’s units. Technology has made the units much smaller and, therefore, easier to carry. The smaller the unit, the lower the firefighter’s profile and the less cumbersome and difficult it is to work with it. When a tool is cumbersome and difficult to operate, firefighters are more reluctant to use and, more importantly, train with it. The controls for the unit may also be much smaller; departments must determine whether firefighters can operate the unit with gloved hands.
  • Weight. The weight of the unit obviously must be considered. The fire service has been trying to reduce the amount of weight the firefighter must carry for years. Weight dramatically affects the ability to effectively use a thermal imaging unit on the scene of a fire for an extended period of time. Obviously, the heavier the unit, the more difficulty the firefighter will have using it. Most of the units available at the present time are relatively close to the same weight. Balancing the weight while engaging in firefighting applications should be considered. Personnel who believe that weight does not make a difference need only try this simple test: Hold a full gallon of milk up to your face or on your helmet for an extended period of time. You will find this to be very tiring.
  • Ease of use. During the evaluation, personnel should be encouraged to operate the unit in full firefighting gear including SCBA and facepiece and performing firefighting functions such as crawling, searching, advancing lines, and so on, since this is how the unit will be operated on the fireground in an uncontrolled environment. Any other use of the tool can only be easier. The majority of the units available today do not have elaborate controls and may be operated while wearing gloves. This type of evaluation will also help determine the compatibility of the particular thermal imager with your department’s PPE ensemble.
  • Training. The fire service is starting to debate the issue of training with thermal imaging units. The question generally is not whether training should be provided. The discussion is over the issues of who should provide the training-the department, a training agency, or the manufacturer-and to what level firefighters should be trained. The debate will not be settled he

    No fire service standards have yet been set for thermal imagers. Contacting other fire departments to learn about their experiences in evaluating, purchasing, training in, and using this wonderful new addition to our arsenal of firefighting tools will help. Much of the learning acquired by the fire service has been through the sharing of our experiences.


    STEVEN P. WOODWORTH is a 15-year veteran of the fire service. Currently, he is a lieutenant with the Atlanta (GA) Fire Department, assigned to the training division. He is a vice president of SAFE – IR, a training company specializing in thermal imaging and firefighter safety training.

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