Firehouse December 2004

Firehouse Magazine, December 2004
Hazardous Materials
By Jonathan Bastian

A number of fire departments have purchased thermal imagers 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

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 see, however, temperature differences on the surface of a container. The essentials at a hazmat scene are:

Remember that 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 types of 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 (e.g., 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. (See 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, as well as while traveling your still district. Use the TI to determine product levels in all of the containers stored in the firehouse. These may be laundry detergent or motor oil containers, pails of paint, or pitchers of water. As you examine items in the firehouse, 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.

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, be careful that you 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. For more ideas and in-depth discussion on using TIs for these and other hazmat applications, visit the Technology section of Firehouse.com.

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 recently driven, 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.

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 they prioritize abatement activities.

For Firehouse.com

In December’s Firehouse magazine, the training article for thermal imaging addressed uses for TIs at hazardous materials incidents. Due to space limitations, the article discussed the task of identifying product levels in containers. While this is a valuable use of thermal imagers at hazmat incidents, it is not the only use. A TI can help in several other ways as well.

First, the TI may help identify the path of spilled product. Knowing the location and movement of spilled product can be especially helpful in determining proper placement for booms and dykes, as well as determining what, if any, evacuations may be required. This can be beneficial for identifying clear products or for tracking leaks in poor visibility (such as at night). If the leaking product has a different temperature than the surface onto which is has leaked, it should be visible with the TI, since the TI detects temperature differences. This will also work with spills in waterways, as long as the spilled product is a different temperature than the water and it is less dense. A gasoline or diesel spill in a waterway can be quickly and efficiently identified and contained. An Illinois fire department responded in the middle of the night to a grounded barge carrying petroleum. Using their TI, they were able to quickly identify the location and severity of the leak coming from the barge. Firefighters created a retention area and saved hundreds of feet of shoreline from environmental damage.

Second, the TI can help identify the source of a leak. In the case of a liquid or solid, by tracking the path of the product, firefighters can find the exact point of release and stop the flow of product to make abatement and containment efforts easier. Effective deployment can also help identify the party responsible for the leak, which determines financial liability for the clean-up effort. For example, law enforcement officials in California used a thermal imager to identify which houseboat in a bay was manufacturing methamphetamine. The chemical discharge from the process left a trail in the water, visible only to a TI because the waste material was warmer than the water in the bay. This trail of waste led directly to the houseboat, and several arrests.

Firefighters can also identify the origin of a gas leak by using a TI. As a gas escapes from a pressurized system, it expands and creates an endothermic reaction. This results in cooling the point of escape. By scanning several cylinders or an entire piping system, firefighters can look for the cold spots to determine the source of the leak.

Many thermal imagers are equipped with temperature gauges, which can help at hazmat incidents as well. Remember, these indicators measure surface temperatures, and they are accurate only under very specific conditions. Firefighters should never make “life or death” decisions based solely on the temperature indicated by the TI. However, if firefighters remember these indicators are “relatively” accurate, they can use them to help make decisions in certain situations. Imagine, for example, a propane container impinged upon by fire. On arrival, the incident commander uses his temperature indicator to determine that the propane container has a surface temperature reading of 100ºF (38ºC). This does not indicate the temperature of the contents, nor is it an accurate temperature reading. The accuracy is lowered significantly because the container is metal; metals generally give artificially cold signals to the TI.

After evaluating the scene, the IC orders hoselines aimed at the container to keep it cool. Ten minutes later, the IC checks the temperature again. If the surface temperature has increased, then his cooling efforts are not effective; his companies are “losing the battle.” He needs to increase the amount of water pouring on the container, or consider a new strategy because his current strategy is not working. If the surface temperature reads 100ºF (38ºC) or lower, then the cooling efforts are effective; they are “winning.”

As mentioned in the Firehouse article, do not forget a TI is not intrinsically safe. There may be certain situations in which it is inadvisable to use the TI as an assessment tool. However, there are a number of ways in which a TI can be used to bring additional information to the incident commander. This information should help firefighters make safer, more informed and more effective decisions.