If you’ve ever seen firefighters respond to a blaze, particularly in the United States, there’s a good chance that you’ve seen them head up on to the roof of a structure to cut a hole in it before tackling the fire itself. Why do they do this?
Firefighters cut holes in roofs to ventilate the smoke and superheated gases to allow firefighters inside to more easily extinguish the fire. This also provides more survivable conditions for victims inside. Not every fire department agrees this is best practice, but the techniques can be productive.
So, let’s take a look at the practice of ventilation and why it’s used in firefighting before we look at some of the evidence in favor and against vertical ventilation as a practice in firefighting.
Why Do Firefighters Cut Holes In Roofs?
When you see a firefighter cutting a hole in the roof of a building, it’s to effect “ventilation” and, in fact, it’s referred to as “venting the roof” by most firefighters because of this.
What is Ventilation in the Fire Service?
The idea of ventilation is part of a host of structural firefighting techniques. Its purpose is to clear the heat and smoke that are trapped within a burning structure so that firefighters are able to see more clearly and locate any trapped people inside as well as tackle the fire in the most effective manner possible.
When big fires suffer from a lack of appropriate ventilation there is a risk that the fire becomes much more difficult to tackle and even more seriously, it’s possible that a build-up of partially burned smoke can eventually lead to a backdraft (different from a smoke explosion). Or, there might be so much heat buildup that it creates a flashover (a simultaneous ignition of everything combustible in a space at once).
Note: Ventilating at the wrong time or when not coordinated with the firefighters inside can actually cause a flashover, rather than preventing it. This depends on whether the fire is ventilation-controlled or fuel-controlled.
A flashover can raise the temperature inside a structure to 1100 degrees Fahrenheit (600 Celsius) or more! This is not a survivable environment, even with all the proper firefighting protective gear.
The Two Types of Firefighter Ventilation
There are two forms of ventilation:
- Vertical ventilation. As the name suggests this deals with ventilation on the vertical plane and when you see firefighters cutting holes in a roof – this is the kind of ventilation that they are doing. This type of ventilation usually works quicker as heat rises, but also requires more time and work to make it happen.
- Horizontal ventilation. As you’d expect this deals with ventilation on the horizontal or lateral plane. If you see firefighters kicking in doors or smashing windows to a burning building, they are trying to effect horizontal ventilation, but there other methods and tools that can be used for effective horizontal ventilation.
They both have similar objectives – to increase visibility, make the interior environment more tenable for firefighters and victims, reduce the chances of extreme fire behavior, etc. They both require very effective timing and coordination to achieve these objectives.
Here is Fresno FD Truck 9, in California, performing vertical ventilation at an apartment fire:
Firefighting Ventilation Tactics
While making holes in buildings can help to begin ventilation processes, often the natural airflow is not enough, and mechanical fans may be brought in to aid the flow of air to the appropriate parts of the burning structure. This is called positive pressure ventilation or PPV.
In high-rise buildings, there may already be a network of fans in place in the stairwells. This can be utilized by firefighters to achieve a similar effect.
There is also a process known as “hydraulic ventilation” where a fog-pattern hose-stream is focused on an opening. This can boost the exhaust rate of smoke, as the water pulls air and smoke along with it.
On small structures, hydraulic ventilation can often reduce the amount of smoke damage that is suffered to the building. On large structures, the technique is usually applied to improve visibility within the structure.
Finally, you may hear of “self-ventilation” that’s what it’s called when a window explodes, or the roof is burned through.
Here is a video showing an example of both positive pressure and hydraulic ventilation combined:
Pros and Cons of Vertical Ventilation
Mark J Cotter writing in the Fire Engineering Training Community in 2018, was highly critical of the practice of vertical ventilation.
He says that recent research has demonstrated that this form of ventilation (except when it occurs via openings that were already present such as skylights or bulkhead doors) could worsen the conditions inside the burning structure.
He says that vertical ventilation is not useful in controlling a fire and exposes firefighters to unnecessary risks and that this danger is no longer justifiable in the face of current firefighting research.
He notes that while many in the North American fire service still advocate for ventilation – the practice is much less common elsewhere and that the reason for this disparity is that training in American fire services has always emphasized the benefits of using vertical ventilation.
He works through a number of examples of fires and demonstrates why they are not suited to using vertical ventilation even though this is the most common practice.
Criticism of Vertical Ventilation (Cons)
Mark Cotter is not along in criticizing the practice of vertical ventilation. In the UK, for example, while lateral/horizontal ventilation is a common practice – vertical ventilation of fires is almost never used.
“USA firefighters ventilate at the top by accessing the roof and making holes to allow the heat and smoke to escape, in theory, that then allows access to the building at ground level which is clear of smoke. I joined Liverpool FB in 1966 and was never trained to do that as it is obviously too dangerous. There are many videos available on YouTube with similar falls through a roof by American firefighters. Yes, health and safety comes more into it now, but we never did that even before HASAWA.”
Many other firefighters on the same thread acknowledge that British firefighters simply don’t use vertical ventilation and they allude to astonishing differences in the death rates between British and American firefighters.
The Number of UK Firefighter Deaths
The UK government no longer keeps a record of the deaths of firefighters on duty. However, it did until the year 2008 and between 1978 and 2008 in the UK, 122 firefighters died while on duty. That is an average of approximately 4 firefighters a year.
There is some dispute as to the accuracy of these figures, however, there’s no suggestion that they are wildly inaccurate, and they serve as a reasonable level of guidance as to fatalities in the UK fire service.
The Number of US Firefighter Deaths
Figures from the United States certainly show that being a firefighter in the US is far riskier than being a firefighter in the UK. In 2018, alone, 64 firefighters died in the United States and on average over the last 30 years or so, more than 100 firefighters die a year in the United States.
Now, even taking into account that there is a huge difference in population between the US and the UK, it is clearly safer to be a fireman in the UK than in the USA.
However, there is nothing in this data that supports the idea that vertical ventilation is to blame for this. In fact, there are major differences in construction and typical structures between the UK and the US and many other differing practices. It’s impossible, without further research, to make any reasonable conclusion as to why firefighters are more likely to die in the USA than in the UK.
Support of Vertical Ventilation (Pros)
Vertical ventilation, when used properly (at the right time, in conditions that have been properly evaluated for firefighter safety, and in coordination with firefighters inside the structure) can be very effective at improving conditions and allowing for more effective and efficient fire suppression. There is no question about whether these tactics work, just about whether they are part of good risk vs. reward decision making.
I, as well as a large percentage of firefighters in the American fire service, believe that vertical ventilation is a very useful tool, when applied properly. That doesn’t mean that it should be used on every fire without question, but it is another tool in the toolbox that can have a dramatic effect on firefighting efforts in the right situations.
“When I first started in the fire service in 1964, we had a lot of 5 story tenements where there were numerous fires over the years. In one case I recall watching a fire as a young fellow before I started as a firefighter. The gas meters were burning and the shut off could not be found (later the gas company found it buried). The building was evacuated and pretty much left to burn until the gas company was able to shut it off.
The fire entered the pipe shaft which carried the plumbing and electrical services to the different floors, reached the ceiling of the 5th floor and mushroomed out. Next was the 4th floor and so on down to the first floor before the gas was shut off. This impressed upon me the strategy and tactics used in dealing with these types of fires. Ventilation early at the pipe shaft with a 10 X 10 sq. ft. hole and aggressive attack with interior lines.
So, let’s go into a fire, it is hot. So hot you are trying to crawl as low as possible. It is dark, you see nothing, even when placing your hand on your face mask it is not visible. You work toward the heat and when you get close enough you might see the glow. Now there are 2 dangers and they are almost the same. First, there is the possibility that the fire is low on oxygen and if it suddenly gets oxygen there will be an explosion called a backdraft. The other is a flashover which is when the room gets so hot that things just ignite all at once. In this case, the first possibility is likely to happen.
All of a sudden, the smoke disappears, the temperature drops by a couple hundred degrees, you can see and extinguish the fire. The truck company just opened up a hundred square feet of the roof, right over your head and the smoke and heat have gone into the atmosphere. The possibility of a backdraft or flashover has been virtually eliminated and you can stand up and stop moving along the floor like a snake. Get the picture?”
Why do firefighters cut holes in roofs? The idea is to ensure adequate ventilation of the fire to reduce the risk of accidents and injury while fighting the blaze. However, as you’ve seen the practice of ventilating fires is not without its critics and it’s much less likely to happen in places like the UK than it is in the US.
While some will argue that mortality rates between the two countries suggest that the UK has the right of this practice – we’d note that there are enough practices that differ between the two nations in firefighting techniques, that isolating a single cause is very difficult without further research.
What we can say for certain is that the practice is likely to continue for the foreseeable future in the USA and other countries where it is favored.