A number of fire departments have purchased thermal imagers (TIs) for their hazmat companies or through hazmat-related budgets (read “WMD and Homeland Security grants”). Whether the TI is assigned to the hazmat company or to a front-line company responding to a possible hazmat incident, it can be an excellent tool for managing these responses. This month’s training tips will concentrate on the applications and limitations of thermal imaging in hazmat. Again, the overall goal is for you to use your thermal imager more, to gain skill and comfort with the tool.
Essentials
Photo courtesy of Bullard
Photo 1 shows how a phase change in certain materials can make a product line more obvious. In this image, the propane truck in the center shows a clear product level. The white signature on the tires and engine compartment indicate that the truck has been driven recently, implying the driver recently on-loaded or off-loaded propane. The truck to the right does not have an obvious product line, nor has it been driven recently. It has not on-loaded or off-loaded propane, and the absence of a phase change has created temperature equalization.
Throughout this series, we have regularly reinforced how a thermal imager functions. Understanding these basics is even more important for firefighters using the TI in hazmat scenes. This tool is not an x-ray device; it does not see through containers. It can, however, see temperature differences on the surface of a container. The essentials at a hazmat scene are:
There is no intrinsically safe thermal imager. If you are concerned about the explosive limits in the atmosphere, then leave your thermal imager in the warm or cold zone. In an explosive environment, your TI could be an ignition source. Thermal imagers do not “see through” most materials, but they can see through some plastic bags. You may be able to seal the TI in a clear plastic bag to protect it from the hazardous material and make decontamination easier, while still being able to see the display screen. If a TI shows a product level, it is not seeing through the container. It is seeing the temperature differences of materials inside the container, which are being displayed on the container’s surface. As a result, a double-hulled or insulated container probably will not show a product level. Some products show a temperature difference only if there has been a recent phase change (i.e., from gas to liquid). When evaluating containers, give consideration to how the presence, or lack, of a phase change may be affecting the thermal image (Photo 1). Because gases equalize pressure, rather than creating a product level, a thermal imager will not help determine how much of a compressed gas is present in a container. Only liquids (including gases stored as liquids) and solids can show product levels. Practice Makes Perfect The most useful function of a TI in hazmat is its ability to help you identify product levels in sealed, non-transparent containers. You can practice your image interpretation skills in the firehouse. Use the TI to determine product levels in containers stored in the firehouse. These may be laundry detergent or motor oil containers, pails of paint, or pitchers of water. You should notice that sometimes you cannot determine a product level. This is not because there is no product, but rather because there is no temperature difference for the TI to detect. While traveling your still district, you should see product levels more frequently because the effects of the sun and weather frequently create temperature differences within the container. Photo courtesy of Bullard Photo 2 shows how a thermal imager can detect the approximate fuel load in this locomotive. At a train derailment, this could be valuable information for the hazmat team as members prioritize abatement activities. For the TI to assist in gauging product level, four key factors must align favorably. First, there must be a product level and a vapor space in the container (the “vapor space” could be an inert liquid or solid, but a vapor space is much more common). Second, there must be a temperature difference between the vapor space and the product. Third, this temperature difference must transfer via conduction and convection to the surface of the container. Last, the background environment around the container must be stable enough for the TI to detect the difference on the container. For example, a warm container in a freezer may not show a product level. When it is compared to the background environment, the entire container is “hot.” As a result, small temperature differences between the product and vapor space are not detected by the TI. As you practice evaluating containers, do not trick yourself into seeing a product level when one is not evident. Clearly, all four factors may not align properly. Items stored at the same temperature for long periods are less likely to show product levels than containers stored in changing environments. Table Talk To ensure your company will use the TI in appropriate hazmat incidents, spend time reviewing your still district and likely response areas. Have each member identify one facility or location where the TI might help with a potential hazmat response. Then ask each member to identify a facility or potential incident in which the risk of an explosive atmosphere may require that the TI be left outside the hot zone. For example, if you have a railroad line in your response area, discuss how the TI may help you manage an incident. Photo 2 shows an image from a locomotive. Would it be helpful in a response to know the fuel load on a locomotive? If so, how and why? If not, why? How might it help with derailed tank cars? Final Report Hazmat incidents are not frequent, but they can pose great challenges. The aggressive use of a TI at a hazmat scene may give the incident commander additional information to make timely and effective decisions. While there are limits to how much the TI can assist responders, in incidents involving sealed containers, knowing the product level may help them formulate the incident plan. Outside of using thermal imagers to detect product levels in containers, the technology can also be used to track the movement of a spilled product in water or on ground, identify the source of a solid or liquid leak, and sometimes identify a leaking gas. Jonathan Bastian is the former thermal imaging training manager at Bullard. He is certified as a thermal imaging instructor by the Law Enforcement Thermographers’ Association (LETA), the international public safety organization specializing in thermal imager certification and training. He is also a member of the NFPA Technical Committee on Fire Service Training. Educated at Brown University and licensed as a high school teacher in Illinois, Bastian served 12 years on the North Park, IL, Fire Department, including the last three as a captain. As health and safety officer, he led the development and implementation of the department’s rapid intervention team SOG. Bastian is a certified Fire Instructor I and Firefighter III, and he spent 12 years as an EMT-I/D. He has taught classes on thermal imaging, rapid intervention teams, and search and rescue operations. Bullard is happy to answer any questions about thermal imaging; contact the company at [email protected].
