Sauna Fires Susceptible to Backdraft Explosion
April 27, 2016
Two recent fires involving saunas in Toronto serve as a reminder to the fire service that this type of fire has the potential to result in significant injury to firefighters due to the increased risk of backdraft explosions.
Backdrafts usually occur when a shortage of oxygen in an enclosed area has reduced the fire to a smouldering state. The high temperatures in an environment starved of oxygen can result in pyrolysis, that is, the chemical decomposition of nearby combustible materials brought about by heat. In the case of saunas, the cedar walls and ceiling can thermally degrade and result in emissions of combustible gases. When such a compartment is opened, the oxygen concentration increases to the point that an explosive mixture may develop as a result. Because of the high temperature created by the fire initially and subsequently when it becomes a smouldering fire, ignition of this explosive mixture can occur without any additional ignition source and may lead to a backdraft explosion that poses serious risks to firefighters responding to the fire.
Analysis of information about past sauna fires revealed that certain circumstances are frequently factors in the ignition of such fires, as outlined in a few examples below:
- improper installation, including not adhering to the minimum clearances to combustibles recommended by the manufacturer;
- tampering or disconnection of critical fail-safe components, such as heat sensors, high limit switches, timing switches, and thermostats; and
- combustible materials, such as towels, left on the heater.
The research clearly showed the importance of having fail-safe components on sauna heaters installed according to appropriate standards. It is also crucial that these components be inspected, tested and maintained in order to prevent conditions that could lead to pyrolysis of the wood and subsequent ignition in the sauna.
Fire departments are encouraged to become familiar with potential fire safety risks associated with fires in saunas, especially the potential for the development of backdraft conditions. Strategies to mitigate these risks are outlined below.
Prevention of Sauna Fires
In regard to buildings that require a fire safety plan and that contain saunas, fire hazards associated with saunas should be taken into account when preparing the fire safety plan. Fire safety plans should provide for the inspection, testing and maintenance of saunas and their heaters. Key considerations also include the following:
- the proper installation of the heater so that it is shielded and properly positioned away from combustibles;
- checks on safety controls, such as automatic high heat shut-offs and timer shut-offs, to ensure disconnection has not occurred; and
- in addition to frequent inspections throughout the day when the sauna is in operation, at a minimum, a mandatory walk-through inspection of the sauna at the end of the operation of the sauna for the day, to make sure the sauna heater is turned off and that no combustible material has been left in the sauna.
Owners should be encouraged to install signage to remind people to keep combustibles away from the heater.
Response to fire or smoke in sauna
In regard to fires involving saunas, fire departments should be aware of the possibility of backdraft and adopt appropriate procedural measures to mitigate risks.
Firefighters must know how to use personal protective equipment (PPE) and self-contained breathing apparatus (SCBA) properly and have a good understanding of their limitations.
In accordance with Ontario Fire Service Section 21 Advisory Committee guidance note #6-6 and Ontario Fire Service Section 21 Advisory Committee guidance note #7-6, fire departments should provide firefighters with appropriate training, information and supervision so that they may understand the various fire conditions they may encounter and the controls required to protect themselves. Fire suppression staff should have a thorough understanding of fire behaviour, rapid fire progression, and hazardous fire conditions such as backdraft.
Enquiries regarding fire risks related to saunas and measures for the prevention of fires in saunas should be directed to Technical Services, Office of the Fire Marshal and Emergency Management; staff members can be reached by e-mail at FireSafetyStandards@ontario.ca. For further information on the Ontario Fire Service Section 21 Advisory Committee, visit the Ontario Association of Fire Chiefs Web site.