Should You Flow Water On Smoke?

October 2026

For years, many firefighters were taught a simple rule: don’t open the nozzle until you see fire.

That idea was usually based on two concerns. First, applying water too early could upset the “thermal balance,” pushing heat and steam down onto victims and firefighters. Second, flowing water before reaching the seat of the fire could cause unnecessary water damage.

Fire behavior research has given us a much better understanding of what actually happens when water is introduced into a hot fire environment. This article will reference a study conducted by the UL Fire Safety Research Institute (UL-FSRI), Impact of Fire Attack Utilizing Interior and Exterior Streams on Firefighter Safety and Occupant Survival: Full Scale Experiments. Their findings challenge both of these traditional concerns.

So the question becomes: If we have hot, turbulent smoke in front of us, do we really need to wait until we can see flames before opening the nozzle?

Remember, smoke is fuel. It contains unburned products of combustion that, given the right mixture of heat and oxygen, can ignite. Rapidly moving, dark, turbulent smoke should get our attention. It tells us that the environment contains a large amount of heat and potentially flammable gases.

Cooling that environment removes one of the key ingredients needed for continued fire growth: heat.

But let’s be clear: this does not mean blindly opening the nozzle every time we see smoke. It means recognizing that the reach of our stream can be used to cool a dangerous environment while we continue advancing toward the fire.

The research gives us some important reasons why.

Myth #1: Water Will Push Heat and Steam Onto Victims

One of the biggest arguments against flowing water before seeing fire was the concern that doing so would upset the “thermal balance.” Firefighters were taught that water introduced into the hot gas layer would turn to steam, pushing heat downward and potentially burning trapped occupants.

We know water expands significantly when it changes from liquid to vapor. In the fire service, we commonly teach that water expands approximately 1,700 times when converted to steam. On its own, that sounds like a good reason to be cautious.

But that is only part of what is happening.

When water absorbs heat, the gases around it cool rapidly. As those gases cool, they contract. During one UL-FSRI experiment, temperatures dropped from more than 1,500°F to below 300°F after water was applied. Although some of the water expanded as it became steam, the hot gases contracted by an even greater amount resulting in a net effect of contraction.

Researchers could see this effect at the openings of the structure. As temperatures dropped, gas flow at the window and doorway briefly changed from an outward flow to an inward flow. In other words, cooling the compartment caused the gases inside to contract.

UL-FSRI also measured moisture levels to determine whether suppression water was creating dangerous steam conditions for trapped occupants. In a bedroom outside the flow path, researchers found no significant increase in moisture near the one-foot level after suppression began. It is also important to remember that the fire itself is already producing water vapor as part of the combustion process.

This does not mean steam does not exist or that nozzle technique does not matter. It means properly applied water is not simply creating a wave of heat and steam that gets pushed down onto victims.

In fact, the bigger effect is the opposite:

Water absorbs energy.
Temperatures drop.
Hot gases contract.
Conditions improve.

For both trapped occupants and firefighters operating inside, removing heat from the environment is a good thing.