Posts tagged: thermal imaging

Gavin Parker, Senior Station Officer with Fire Rescue Victoria, discusses Identifying hazmat spills, leaks and reactions using the Thermal Imaging Cameras (TIC)

An application for the use of Thermal Imaging Camera (TIC) during hazmat incidents along other uses can include the detection and monitoring of spills, leaks, material energy variations, and reactions.

There are many factors to consider for interpretation of the image, including the apparent and measured temperature.

Assessment methods

The camera allows “non-contact” assessment. This can allow some investigations to be done from a safe distance and location, increasing the safety of responders, and includes information that may not otherwise be available visually.  

During scene evaluation, we can use quantitative and/or qualitative assessment.

Qualitative thermography refers to obtaining visual representation of apparent temperature variations of surfaces, rather than precise temperature measurements.

It compares the contrast or thermal appearance of objects and requires an understanding of the effects of heat transfer, reflections, emissivity, and other factors affecting image interpretation and the variables and limitations of the image produced.

This includes greyscale shades and/or colours referenced against the screen temperature scale that represent different energy levels, allowing for a quick and intuitive interpretation of the image.

Quantitative thermography includes Direct Temperature Measurement (DTM) with actual temperature values within the thermal image and requires an understanding of variables and limitations of IR temperature measurement.

Qualitative assessment may be adequate for most tasks. The assessment of challenging or changing conditions and temperatures can be achieved with both qualitative and quantitate assessment using one or a combination of methods, including:

• A baseline is used to establish a reference point of the product, equipment or process operating under normal conditions and in good condition, a baseline is a good starting point to identify anomalies.
• Trending inspections can be used to compare how energy is distributed in the same component or material over time. This can help detect ongoing changes.
• Comparative assessment is a process that is used to compare similar components or products under similar conditions to assess the condition of the object being viewed. 

Methods of identifying and monitoring changes and reactions

There may be a need to identify or monitor temperature changes and reactions in products or processes. Energy variations may be identified using the apparent temperature of the displayed image. DTM can be useful in hazmat situations and may allow the operator to determine or monitor energy levels.

Some examples include:

• Identify and monitor adiabatic expansion from a gas flow or leak resulting in a decrease in temperature
• Exothermic or endothermic reactions that may result in an increase or decrease in temperature
• Identifying a change of state that may produce a change in temperature
• Chemical reactions and energy changes within a container or in the open air
• Determining high energy levels that may indicate potential for a container or component failure
• The effectiveness of cooling or correcting a reaction

Identifying gas leaks

The TIC can be used in conjunction with traditional equipment and other sensory inputs, this includes signs of damage, condensation, icing, vapour haze, and what can be determined audibly with the sound of leaks.

While there are some gasses that can be seen, most gasses released into the atmosphere will be transparent visually.

Each type of gas absorbs and emits infrared radiation at specific wavelengths. Fire service cameras operate in the long-wave IR (LWIR) region.

When a gas is leaking into the atmosphere, most will not be able to be identified with a fire service TIC.

The selection of IR equipment and wavelength depends on the gas being detected.

For industrial applications, identification, and detection can be achieved with specialist fixed or portable equipment and sensors for the specific substance or range of products that they are designed to detect, such as Optical Gas Imaging (OGI) equipment with most operating in a very narrow spectral range of Mid-Wave infrared (MWIR, 3-5 microns) and some in LWIR.

In some cases, for example, a leaking liquefied gas such as Liquefied Petroleum Gas (LPG), when it’s between a liquid and gas state, may be identified at the point of the leak as a vapour, either or both visually and in LWIR until it transitions to a gas state.

When a liquefied or high-pressure gas is leaking it may create an adiabatic expansion reaction.

This is a result of a change from the equilibrium of pressure within the system due to the rapid expansion of the escaping gas that may present itself on surfaces in IR as it cools the cylinder, plumbing, or objects in contact.

This can occur at the point of the leak or within the system itself. Factors that will affect this are the quantity of gas, pressure difference, and insulation of the object.

Another consideration is the cooling effect the escaping gas may have on the surface of objects in the vicinity of the leak such as walls, floors, ceilings, or other objects.

This may also depend on the quantity and pressure as well as if the product is heavier or lighter than air.

Leaks from pressurised underground pipes may indicate as surface cooling at the point of surface release.

Determining the rate of gas leaks

We may have no way of measuring the quantity of pressurised gas leaking using a fire service TIC, we may, however, be able to determine the extent of the leak and if the leak is decreasing, consistent, or increasing, by examining the effect of cooling using a combination of image indicators or DTM of the scene over time.

Liquid leaks, spills, and factors affecting surface moisture detection

The camera can assist hazmat crews to determine the levels of liquids and solids in storage containers as well as spills and leaks of liquids on the ground.

It can also identify spills of some liquids that are lighter than water and may be identified in rivers and other bodies of water.

Leaks into waterways

The camera may assist in determining the point at which the leak originated and for liquids the spread, shape, and size, as well as the point of entry and exit to and from drainage and water courses.

It may also provide us with information on the effectiveness of containment devices such as absorbents and booms.

A spill into a waterway can only be identified if the product floats on the surface. A thermal imager cannot detect a material below the surface.

Background reflections on flat water surfaces from objects such as clouds and trees, for example, may be mistaken as the outline of a leak because of how they appear thermally.

Surface leaks and spills

IR detects surface temperatures and as liquids evaporate energy is exchanged. This evaporation cools the surface.

Factors such as the surface area, the type of surface, air flow, temperature & Relative Humidity (RH), vapour pressure, and volatility of the product will affect evaporation rates.

The volatility or evaporation rate of the liquid is a factor to consider in evaporation. Volatility describes how easily a substance will vaporize (turn into a gas or vapour).

At a given temperature, substances with higher vapor pressure will vaporize more readily than substances with lower vapor pressure.

A volatile substance can be defined as a substance that evaporates readily at normal temperatures and/or one that has a measurable vapour pressure.

Identifying liquid leaks and spills on solid surfaces

While some liquid spills may be invisible to the naked eye, many hazardous materials can also be seen with a thermal imager because of the differences in temperature between the material and the ground’s surface.

Factors influencing detection include the amount of product present, its properties, background energy, evaporation rate, ground vegetation, and type of ground surface.

Limitations

Not all TICs are intrinsically safe. In all cases, thermal contrast, environmental factors, background radiation and emissivity of surfaces, equipment limitations with image quality, and the range and accuracy of temperature measurement may also impact our ability to identify objects with the TIC.

Conclusion

The use of TICs can greatly enhance our capability for fires and incidents, this includes their use in hazmat incidents. It’s also important to consider that the information presented may not always be conclusive or accurate.

TICs are a valuable tool and when utilised correctly can assist in making operations safer, effective and increase efficiency.

In all cases standard hazmat procedures and the use of appropriate PPE/PPC should be followed, a TIC should only be used as an additional aid to those standard procedures.

Author’s note

The procedures and views expressed are that of the author and not necessarily those of any agency or organisation.

This article was originally published in the April 2024 issue of International Fire & Safety Journal. To read your FREE digital copy, click here.