We have all heard the saying “put the wet stuff on the red stuff” and as true and basic as it sounds there is a lot more that goes into than that. Every firefighter on the fire ground – from the nozzle man, to the company officer making tactical decisions on how to attack the fire, all the way to the chief officer overseeing and defending these operations – should have a basic understanding of fire flow and ways to determine fire flow requirements based on the building they are operating in.
When determining fire flow our main goal is simple; cool the involved combustibles dropping them below the temperature at which they produce ignitable vapors and heat to support fire growth. This as we all know is done by fire suppression and can be accomplished in 2 ways. Directly attacking the fire and indirectly attacking the fire. Without going in to detail on this it is simply put that direct attack is flowing water directly on burning solid materials and indirect is flowing water onto the overhead smoke layer and thermal layer to disrupt the flow of heat and combustible gases.
So with that being said, why do we need to understand the importance of fire flow?
For starters, a lot has changed in the fire service over the last 15-20 years and let’s begin with defining heat release rate. This is the amount of time needed for a given fuel depending on its mass to produce enough energy, also known as heat, to influence combustion. Fifteen to twenty years ago our fire flow was calculated at 95 & 125 GPM (gallons per minute) for a safe and efficient flow. Nowadays due to changes in society a safe an efficient fire flow is now calculated at 150 & 200 GPM. In those years back fires would reach flashover conditions within an estimated 10 minutes of ignition. Today, they are reaching flashovers in less than 4 minutes.
Without talking building construction and the transition from legacy construction into the development of the modern day lightweight construction (truss) as well as hybrid construction, and we can save that discussion for another day, one other reason fire flow is said to be important is due to more plastic products being developed. These have a combustion rate of 3 times of traditional Class-A combustibles. Plastics are derived from petrochemicals (hydrocarbons) and are found in almost every consumer product on the market today. With the creation and advancements in modern computer aided dispatching systems, fire departments are arriving sooner to alarms and at times making entry the same time the fire is reaching flashover conditions.
To determine your ever so important fire flow, these factors come in to play:
- Size & type of structure (residential/commercial/industrial)
- What and where is your water supply?
- Apparatus tank size and pump capacity
- Hose and nozzle configuration
- What’s your crew size and their average response times?
With that being said remember this, the minimum fire flow must be capable of absorbing the maximum potential heat release rate to immediately prevent the fire from transitioning to the flashover stage.
Until next time; work hard, stay safe and live inspired.
About the Author
NICHOLAS J. HIGGINS is a firefighter with 14 years of service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.