Backdraft and Smoke Explosion: Part 8

Smoke Explosion Recognition and Mitigation

Smoke explosions (and backdrafts) are an infrequent occurrence on the fireground. Firefighters and fire officers need to develop their situational awareness by recognizing key fire behavior indicators and reading the fire.

While having a small number of fires is desirable for the community, firefighters have limited opportunities to gain the experience necessary to develop a sound understanding of fire behaviour through experience alone. Compartment fires can lead to various scenarios depending on the fuel type, arrangement and quantity, access to the oxygen, compartment material, and any fire suppression system activation. Being able to anticipate fire and smoke behaviour will help prevent the firefighter injuries and fatalities in fire operations (Rasoulipour, 2022, p 1).

Recognizing Potential Smoke Explosion Conditions

One of the challenging things about smoke explosions is that the only real indicator is the presence of smoke and if there wasn’t any smoke, they likely wouldn’t have called us. That said, the conditions that result in potential for a smoke explosion are an excellent starting point for identifying potential indicators.

Requisite Conditions

Fleischmann, Madrzykowski, and Dow, (2024) identified a consistent cycle in development of conditions necessary for an overpressure event such as a smoke explosion within a combustible fire compartment. This cycle consisted of three phases:

Axisymmetric Plume: An axisymmetric plume is a fire-induced flow where hot gases rise vertically from a heat source, expanding outward in a symmetrical, conical shape. This is normal fire development beginning with a single fuel package. This phenomenon will be observed regardless of occurrence of a smoke explosion or other extreme fire behavior phenomena. This may be where the transition to a ventilation limited fire begins.
Detached Flaming: Where flames detach from the burning fuel package and move through the smoke layer. Detached flames in the smoke layer is also referred to as ghosting flames and is an indication of a ventilation limited fire (Sugawa, Kawagoe, & Oka, 1991; Chen, 2013; & Rasoulipour, 2022). Ghosting flames are an indication of a significantly ventilation limited fire.
Smoldering Phase: If a fire in an enclosure involves a fuel that has a propensity for smoldering combustion such as wood (cellulosic) products, polyurethane foam, etc., when the oxygen concentration is insufficient to sustain flaming combustion, the fire is likely to begin to smolder. Pyrolysis will continue and the concentration of flammable products of pyrolysis and combustion will increase, while temperature is reduced.

As previously discussed, as the ventilation-limited fire enters the decay stage and begins to smolder, the HRR and resulting temperatures will become lower, reducing pressure within the enclosure. As pressure drops, the exhaust of smoke through leakage points will become less pronounced and may cease entirely as the leakage points become air inlets. Intake of air will result in regrowth of the fire with increasing HRR and temperature, returning the leakage points to exhaust openings for smoke. The increased HRR results in increased oxygen consumption, resulting in the cycle repeating itself (Bengtsson, 2001 & Lambert & Baaij, 2011).

With pulsating fire development, there is sufficient temperature is maintained for ongoing pyrolysis of building contents and structural materials, increasing the concentration of flammable pyrolysis products in the smoke. When pyrolysis continues and oxygen concentration (which decreased as the fire became ventilation limited) increases as pulsing air flow brings additional atmospheric oxygen into the compartment, increasing the oxygen concentration and bringing the mixture of smoke and air into the flammable range providing conditions that may result in a smoke explosion.

Indicators of Potential for a Smoke Explosion

Fleischmann, Madrzykowski, and Dow, (2024) identify several interrelated indicators of potential for an overpressure event (OPE) such as a smoke explosion in the fire compartment. It is important to note that some of these are simply indicators of a ventilation limited fire and many of these indicators have a great deal in common with indicators of potential backdraft.

Fire in significantly ventilation limited compartments, such as attics or void spaces, increase the potential for an overpressure event such as a smoke explosion or backdraft.
Detached flames in the smoke layer are not identified as an indicator by Fleischman, Madrzykowski, and Dow, but are specified as a common precursor. However, observation of ghosting flames while operating inside an enclosure is an indicator of a significantly ventilation limited fire.
The potential for an overpressure event is increased once the fire has spread to where large surface areas of smoldering fuel, such as wood, are involved. This indicator may be combined with severely ventilation limited compartments when the fire is in an attic or void space with combustible linings.
Pulsing air flow, with smoke pushing out alternating with air in at ventilation openings may be an indicator of potential for an overpressure event such as a smoke explosion. Note that this is also an indication of potential for a backdraft if there is a change in the ventilation profile.
An overpressure event can occur without any change in ventilation. This is a significant difference between a smoke explosion and backdraft. This significant difference was also identified by Fleischman and Chen (Fleischmann & Chen, 2013).

Multiple overpressure events such as a smoke explosion may occur in the same area if no action is taken to change the conditions. However, an overpressure event may change conditions, by causing failure of windows or changes in the ventilation profile of the building, which can have a significant impact on subsequent fire behavior.

None of the experimental research to date has examined smoke explosions occurring in compartments remote from the fire. However, empirical evidence provided by examination of structure fire incidents where overpressure events occurred points to this other potential smoke explosion scenario. The following two incidents provide an example of overpressure events, concluded to be smoke explosions that occurred remote from the fire area:

On March 26, 2008, Los Angeles City Fire Department Firefighter Brent Lovrien died in the line of duty, and Engineer Anthony Guzman was seriously injured when forcing entry into an electrical room adjacent to a fire in an underground utility vault. Sparks from a composite metal cutting blade on a rotary saw ignited the premixed smoke (products of pyrolysis and combustion) and air within the electrical room, resulting in an explosion. For additional details on this incident read NIOSH Death in the Line of Duty Report 2008-11 (NOSH, 2009a) and the Los Angeles Fire Department news post 15^th Anniversary of the Line-of-Duty Death of Firefighter Brent Lovrien (Prange, 2023).

On February 22, 2008, a deputy chief and eight firefighters were injured during an explosion at a restaurant fire in Durango, Colorado. The fire originated in a ceiling void of a restaurant with smoke pushing through structural openings into multiple ceiling void spaces of two exposures. Flames pushing through structural void openings between the main fire occupancy and exposures resulted in ignition of premixed smoke (products of pyrolysis and combustion) and air within the ceiling voids, resulting in an explosion that significantly damaged the building and injuring the chief and firefighters. For additional details on this incident read NIOSH Death in the line of duty report 2008-11 (NIOSH, 2009b), the Durango Fire Department Investigation Report (Hanks, 2008), and the Fire Behavior Case Study-Durango, CO (Hartin, 2009).

In each of these instances, there was a ventilation limited, smoldering fire remote from where the smoke explosion occurred. The only direct evidence of a potential smoke explosion was the likelihood of a smoldering fire which allowed accumulation of the mixture of smoke and air remote from the fire area. In one of these instances, the source of ignition was independent of the fire and in the second instance, ignition resulted from fire extension into the void spaces containing the flammable mixture of smoke and air.

Mitigating Smoke Explosion Conditions

There are two basic tactics to mitigate or reduce the risk of smoke explosion:

Water Application

Effective application of water into the compartment can prevent an overpressure event such as a backdraft or smoke explosion (Fleischmann, Madrzykowski, & Dow, 2024). This is particularly true when addressing potential for smoke explosion in the fire compartment. While the research on smoke explosions did not specifically involve experiments focused on mitigation, it is likely that appropriate application of water (resulting in vaporization of the water within the fire compartment) will increase the mass fraction of inert products and reduce the mass fraction of fuel within the mixture of smoke and air, moving it out of its flammable range (Gottuk, Williams, and Farley, 1997 & Weng and Fan, 2002)

Tactical Ventilation/Anti-Ventilation

Ventilation of spaces that have accumulated pre-mixed smoke and air can mitigate the potential for occurrence of a smoke explosion in areas remote from the fire. In some cases, this is easily accomplished and in other cases it is complex and challenging. Anti-ventilation, in this case using positive pressure fans to pressurize exposures and prevent smoke infiltration and mixing can be effective in mitigating the potential risk of a smoke explosion in areas remote from the fire.

Practical Approaches

Methods for water application are essentially the same as those used to mitigate backdraft potential. However, it is important to recognize that no change in ventilation is needed for occurrence of a smoke explosion.

Use of one or more piercing nozzles.
Cobra cutting extinguisher (or similar device)
Brief and limited opening of a door and application of water with an attack line.

Tactical ventilation can be performed following mitigation through the application of adequate water into the enclosure.

When addressing potential for smoke explosion in uninvolved compartments and voids remote from the fire area, focus on proactive use of anti-ventilation to prevent smoke infiltration as well as ventilation of smoke logged compartments and possibly anti-ventilation once the smoke has been removed to prevent re-infiltration.

Pressurize uninvolved, attached exposures to prevent smoke infiltration.
Ventilate uninvolved, attached exposures that are smoke logged (use caution here to ensure that there is no significant extension into the exposures prior to ventilation).
Consider pressurization of uninvolved attached exposures, post ventilation to prevent re-infiltration of smoke.

Understanding the Risk

It is essential to maintain a balanced perspective. While backdrafts and smoke explosions are a hazard and present risk to firefighters operating at a structure fire, occurrence of these phenomena is rare. Understanding the mechanisms underlying these fire behavior phenomena, the requisite preconditions, potential indicators of a potential overpressure event, and approaches to mitigate or reduce the risk minimize the potential for firefighters’ injury or death.

References

Chen, Z. (2013). Smoke explosion in severely ventilation limited compartment fires. Retrieved June 16, 2025, from https://bit.ly/4472aUB.

Rasoulipour, S. (2022). Experimental investigation of the smoke explosion phenomenon. Retrieved June 11, 2025, from https://bit.ly/43XccaI.

Fleischmann, C., Madrzykowski, D., & Dow, N. (2024). Exploring overpressure events in compartment fires. Fire Technology, 60, 1867–1889. Retrieved June 26, 2025, https://bit.ly/4kOKlB0.

Sugawa, O., Kawagoe, K., and Oka, Y. (1991). “Burning Behavior in a Poor-Ventilation Compartment Fire – Ghosting Fire.” Nuclear Engineering and Design, 125(3), 347-352

Fleischmann, C. & Chen, Z. (2013). Defining the difference between backdraft and smoke explosions. Procedia Engineering, 62, 324 – 330.

National Institute for Occupational Safety and Health (NIOSH). (2009a). Death in the line of duty report 2008-11 career fire fighter dies and a career engineer is seriously injured investigating smoke resulting from a manhole fire – California. Retrieved July 16, 2025, from https://bit.ly/3TG6lCb.

Prange, N. (2023). 15^th anniversary of the line-of-duty death of Firefighter Brent Lovrien. Retrieved July 16, 2025, from https://bit.ly/3IxgIFU.

Hanks, K. (2008). Durango Fire & Rescue Authority fire investigation (explosion) report Incident #00001-2008-000718-00, 750 Main Avenue, February 22, 2008 @ 1340 Hours. Retrieved July 16, 2025, from https://bit.ly/3IpSygH.

National Institute for Occupational Safety and Health (NIOSH). (2009b). Death in the line of duty report 2008-03 nine fire fighters from a combination department injured in an explosion at a restaurant fire – Colorado. Retrieved July 16, 2025, from https://bit.ly/44QMBR8.

Hartin, E. (2009). Fire behavior case study: commercial fire Durango, CO. Retrieved July 16, 2025, from https://bit.ly/4lqWXhT.

Gottuk, D.; Williams, F.; & Farley, J. (1997). The development and mitigation of backdrafts: a full-scale experimental study. Fire Safety Science, 5, 935-936. doi: 10.3801/IAFSS.FSS.5-935

Weng, W. & Fan, W. (2002). Experimental study on the mitigation of backdraft in compartment fires with water mist, Journal of Fire Sciences, (20)4, 259-278. doi: 0.1106/073490402029761.