Gavin Parker, Senior Station Officer with Fire Rescue Victoria, looks at Thermal Imaging Cameras for identifying product levels and conditions in containers

The use of thermal imaging cameras (TICs) can greatly enhance our capability for fires and incidents. This includes their use for hazmat response to assist in identifying product levels and energy conditions in containers.

To identify product levels, hazmat responders typically use available resources such as level gauges, sight glasses, or probes to physically measure the volume or depth of the material. Firefighters can also use the TIC without direct contact to determine product levels, temperature conditions and changes. This can assist in determining the appropriate response and containment measures from a distance.

The product levels that may be identified can be either solids such as powders or grains, liquids stored at atmospheric pressure or liquefied gases stored under pressure or refrigeration. TICs are not reliable for measuring gas levels. Gases cannot be detected in the same manner as liquids because the impact of any energy transferred to the surface may be equal throughout the entire container. Therefore, gas-filled containers, regardless of product quantity unless liquefied, may appear as one consistent shade.

We may be able to identify product levels in containers of all shapes and sizes. Thermal imagers cannot “see through” the container, the product in contact with the outer surface of a container conducts energy through its wall at a different rate than the air space above. If thermal contrast exists, the TIC may indicate a product level as a variation in screen shades between the contents and the air space.

Limitations and considerations

Limitations of the cameras use for hazmat use include, but are not limited to the following:

• Intrinsic safety – Not all thermal imagers are intrinsically safe and those that are not shouldn’t be used in areas that require the elimination of ignition sources.
• Emissivity of surfaces – A measure of the viewed surface’s ability to radiate thermal energy compared to a perfect emitter of energy. These can vary between low emissivity surfaces that are shiny, polished, and gloss painted and those that have high emissivity, for example, a rough or matt finish, or ones that are tarnished, oxidised, or have contaminants such as dirt and grime on the surface.
• Container construction – Insulated or double skinned containers may hide the thermal signature of the contents.
• Background radiation – Absorbed or reflected energy from the sun, cold celestial radiation from clear sky or other background objects may produce a false indication of product levels or other anomalies.
• Environmental factors – Wind, rain, ambient air temperature and other environmental factors that may provide inaccuracies.
• Thermal equilibrium – If the container, product, and the airspace are all equal in temperature, producing a thermal image with an even shade with no thermal contrast of the product level.
• Thermal capacitance – The airspace at the top of the container may warm up and cool down much faster than the product in the container. This allows us to identify the product level if thermal contrast exists.The thermal capacitance of the container and products, particularly between liquids and solids such a grains or powders may vary.
• Equipment limitations – Sensor resolution, camera features and functions, distance to spot ratio (D:S), temperature range and Direct Temperature measurement (DTM), most cameras are limited to a display in whole numbers only, also reducing accuracy.

There are many factors affecting the image produced, and any apparent or measured temperature accuracy. It is important to remember that the information presented may not always be definitive.

We need to consider the construction, shape, surface, and finish of the container that you are going to inspect. Containers with a smooth, shiny finish may have low emissivity and reflect energy from the surroundings. This can give an inaccurate indication of the actual surface temperatures and energy.

If a container appears as one shade of grey or colour on the viewing screen, it could be full, empty, or partially filled and in thermal equilibrium, with the product, air space and container at or near the same temperature. In that case, regardless of the product level it may indicate as a single screen shade.

Throughout a 24-hour cycle of warming and cooling from ambient temperature or energy from the sun, the product and air space may cycle through thermal equilibrium at different times. Containers stored in an even temperature environment and shaded from the sun are more likely to have the product and airspace in thermal equilibrium. If appropriate and safe to do so, cooling a section of the cylinder with a water spray may cool the airspace and provide some thermal contrast of the product level.

In other examples, the insulating properties of containers, background energy from the sun, cold energy from the sky, partial shade or other environmental factors may prevent indication of the product level or provide indications of incorrect levels and other anomalies. In some situations, the camera operator may be able to use other similar containers on site with the same construction as a reference or as a comparison.

Experience with the camera, products and containers is key to understanding and working within any limitations.

The use of the TIC should be done in conjunction with appropriate PPE/PPC, a risk assessment, correct operational procedures and other equipment and practices such as air monitoring that would normally be used.

The camera may enable assessment from a safe distance reducing exposure, without direct contact of the container(s) or products. If required, the cameras digital zoom feature can also be used if available.

Use appropriate camera modes and compare to standard mode (TI Basic) as a benchmark. Where possible and if safe to do so, inspect containers from several sides. With horizontally mounted cylinders and tanks, check each side, each end as well as an angle to take in two sides at once. With upright mounted tanks, if possible, check from several angles.  For all containers consider the impact of sunshine for radiant energy, reflections, shadows and if the sky is clear, for cold celestial reflections.

Compare with what can be seen visually with any anomaly identified or the product levels detected for the potential influence of background energy and/or the emissivity of the surface. These can be because of direct sunshine, shade, painted surfaces, or other factors that can affect the thermal view.

DTM can also be done at several points; at, above and below the product level, this can also verify what has been identified on the screen display.

Chemical or processing temperature reactions may also be identified and monitored. For any application and ongoing assessment, record the DTM of the product and airspace as needed and capture images or record video if required.

Inspection results

Information gained will assist in determining product levels, the potential of any leaks, and the possible requirements for containment or decanting of containers.

Identify if any anomalies exist and verify them if possible. Some large liquid storage containers may have a “sludge” build-up that can settle as an uneven level or have two or more liquid products that may have separated due to their specific gravity that may indicate multiple product levels. Solid materials such a grain or powders may have product levels that also appear uneven.

Conclusion

In all cases standard hazmat procedures must be utilised to identify product levels at hazmat incidents, a TIC should only be used as an additional aid to those standard procedures. Ensure that you are familiar with the TIC that you are using and any additional features or functions that can assist.

It is important to remember that the information provided may not always be accurate.

The interpretation of thermal imaging results can be complex and may require specialised training or expertise. Understanding the characteristics of different containers, materials and being able to recognise potential hazards based on experience, training, and a solid understanding of image interpretation are critical in the effective and successful use of thermal imaging in Hazmat situations.

This exclusive article was originally published in the June 2023 issue of International Fire & Safety Journal. To read your FREE digital copy, click here.