Can Thermal Imagers Help During a Flashover

Jul 14, 2022

Flashovers are extremely dangerous and have claimed the lives of too many firefighters over the years. Many articles and training programs have been produced to help firefighters understand a flashover situation and how to escape safely. In a flashover, fire conditions progress rapidly from a hot fire to what becomes fire that is inescapable.


As an instructor, I have heard firefighters say that a thermal imager can help you during a flashover. This is not true. A thermal imager is a tool to help detect a flashover, but it cannot help you if you are caught in one. Think about the amount of time or lack of time, you have in a flashover. You only have a few seconds to get out of that situation and must move quickly. In this type of scenario, you don’t have time to look at your thermal imager.

A preflashover situation is where a thermal imager can help. The thermal imager can give you a visual indication of warning signs that you would otherwise not see. Without the use of a thermal imager, the thick smoke acts as a visual barrier to what is going on above you. Convective velocity, thermal layering, and even rollovers are often hidden inside the smoke and are difficult or impossible to detect. The thermal imager can help you visualize these events. The thermal imager can help you identify how rapidly the fire gases are moving across the ceiling, indicating that the gases have someplace to go other than the room you are in. Thermal layering is also visible to the thermal imager. When any of these two visuals change (convective velocity slows or thermal layers descend), it can serve as an early indicator of potential flashover conditions.

The key part to staying safe when entering a burning building is to always have your thermal imager with you to scan a room prior to entry. This is so important when avoiding a flashover. Scanning with your thermal imager enables you to look for signs of excessive heat buildup, particularly near the ceiling, or levels of high heat closer to the floor where you might not otherwise expect it. The thermal imager will also help you locate potential vertical or horizontal vent points in case you need them and where the secondary means of egress are located. In a flashover situation, these tactics are lifesaving.

The thermal imager is there to help you recognize the danger that you may encounter before it happens so you can avoid the danger and go home safely. Simply put, if you have no other means of control such as ventilation or a hose stream, you must get out quickly. If you wait until the flashover is taking place, it is too late for the thermal imager to help you escape this extremely dangerous occurrence.

1. The importance of conducting flashover training to recognize the signs.


2. Recognizing the preflashover signs is important; this is “the calm before the storm.”


3. Understanding fire behavior.


4. A fully developed fire.


It is important to note that the temperature-sensing feature or Relative Heat Indicator (RHI), as it is often called on your thermal imager, is not a reliable indicator of flashover or preflashover conditions. It cannot accurately detect the temperatures of gases, which is where the greatest threat usually lies in the growth stage of a fire. The thermal imager is designed to detect surfaces, not gases. RHI is best used when evaluating the temperature differences in the same or similar materials. For instance, when performing overhaul, you might use the RHI feature to tell you what portion of drywall is hotter than another portion of drywall. When comparing like materials, the actual temperature displayed does not matter as much as the difference between the temperatures.

Fortunately, a flashover is not a routine occurrence but a culmination of successive, prior events that can lead to a potentially catastrophic outcome for firefighters. It is these preflashover events that you must be aware of. In the same way that you use a thermal imager to size up a building prior to entry, you must constantly size up the interior conditions of a fire environment and be observant of change. Once you see the changes coming, you can find a path out of harm’s way.

Many fire departments have training facilities that include flashover or live fire simulators. However, not all departments have that luxury. Training as a firefighter is paramount to understanding fire behavior, stages, and dangerous conditions. If training facilities are not available, there are training props available such as “wooden dollhouses” you can build, or you can use a Max Fire Box, which can enhance your department’s knowledge of these conditions.


This article by Manfred Kihn was published in Fire Apparatus Magazine in the March issue of 2022.