Understanding Time to Occupation and its Effect on Victim Survivability
By: Jake Hoffman
As the modern firefighter has more information at their fingertips than ever before, the spread of new (or tried and true) techniques and ideas is extremely fast. However, with a constant stream of print and social media articles, videos, and research projects, it is quite easy for anyone to become overwhelmed with information. While understanding terms and concepts such as heat flux and heat release rate are important for firefighters to comprehend as they relate to modern fire behavior, this knowledge must not come at the expense of basic firefighting concepts such as friction loss and forcible entry techniques.
In our fast-moving society, people have a thirst for new information lest they be left behind. Too often however, many in the fire service are quick to embrace the shiny, new concept while discarding tactics that have been proven through decades of experience.
Whether your department chooses to employ transitional attack or relies on placing the first line on the interior between the fire and potential victims, one thing is clear, no one has ever been saved from the bushes. If you choose to employ an exterior stream prior to making entry to the structure, it is imperative that you transition to the interior as quickly as possible to give any trapped victims the greatest chance of survival.
The recent UL Firefighter Safety Research Institute project “Study of the Impact of Fire Attack Utilizing Interior and Exterior Streams on Firefighter Safety and Occupant Survival” (UL Study) evaluated how air entrainment, water mapping, and various techniques affect conditions on the interior.
Regardless of staffing, rapidly gaining entry to the structure should be the highest priority of the first arriving unit at a building fire whether in rural or urban America. Regardless of the attack method chosen, firefighters must minimize time to occupation to maximize victim survivability.
“Although survivable spaces exist at the time of fire department arrival, the survivability
potential decreases as the time of exposure increases.” – UL Study pg. 180
“Time to occupation” is defined as the time between arrival of the first fire apparatus and when that crew crosses the threshold of the door. Necessary tasks such as 360, forcible entry, and deploying the attack line must occur prior to entry, but by completing these tasks as expediently as possible, the attack crew gives any potential victims the greatest chance of survival. While transitional attack maylower temperatures inside the structure, smoke inhalation, not burns, is responsible for the majority of fire deaths in the United States.
The study of victim survivability is relatively new and itsterminology may be foreign and confusing to many firefighters. Fractional Effective Dose (FED) is defined as “the dose received in a given time divided by the effective dose required for a desired endpoint, whether it be incapacitation or death.” For purposes of the UL study, anFED of 1 was considered the amount of heat flux that would kill approximately half of the population (LD50). Referencing gas concentrations, an FED of 1 represented a dose that would cause incapacitation (unconsciousness) and a FED of 3 described a dose that would kill approximately half the population (LC50). Removing a victim from the IDLH as soon as possible after arrival is essential to minimizing the FED, therefore increasing their chance of survival. As the Fractional Effective Dose is a function of the time a victim is exposed to the hazard (whether it be heat flux or fire gases), the earlier into an incident that the victim is removed from the IDLH, the less FED they have been exposed to and the greater their chances for survival.
After a victim has been located inside a fire building, their presence will typically be announced via radio and removal begin. Removal methods will differ based on variables such as heat and smoke conditions, victim size, staffing, etc. Depending on where a victim is found inside a structure fire, consideration should be given to removing the victim through a window or even sheltering the victim in place behind a closed door in lieu of exposing them to additional heat and smoke during a lengthy removal. These techniques have been used with great success in departments large and small across the country, however some in the fire service will discredit their effectiveness as they are not in basic firefighter curriculum and textbooks. By removing the victim as quickly as possible and without exposing them to additional heat, smoke, and fire gases on the exit, we are limiting the FED that the victim is exposed to, thereby increasing their chances of survival.
As explained in UL Study Tactical Consideration 7.5 – Fire Attack and Search & Rescue Can Occur Simultaneously, “Finding them (victims) is the first step to removing them, and therefore searches need to start as soon as possible.”
At the end of the day, the fire department has been called to do what civilians cannot, and that is place a handline on the interior of the structure to effect and support searches for and rescue of trapped victims. Regardless of your initial attack method, the time to occupation MUST be minimized to maximize the chance of victim survivability.
Jake Hoffman is a Private with the Toledo Fire Department. He served as a panel member for the UL Study of the Impact of Fire Attack Utilizing Interior and Exterior Streams on Firefighter Safety and Occupant Survival.