Have you ever walked through an urban area and noticed you’re stepping on glass? We don’t mean a smashed beer bottle after a night out, but rather the glassy parts of the pavement itself. You may have never stopped to wonder why they exist, but they’re actually one of the most important elements of fire protection when it comes to basements and other underground constructions.
These fixtures are common around London and other UK cities, and are called pavement smoke outlets. As their name suggests, they allow smoke out from a basement in the event of a fire. They don’t even have to be made out of glass — but we’ll touch on that in a second. So, how do pavement smoke vents work? Let’s find out.
Before we get down to brass tacks, we need to understand why basements require a special ventilation system in the first place. These below ground level rooms are becoming more and more sought after due to property space being limited in the UK. However, whether you’re in the process of a conversion or building a dwelling from scratch, it’s vital to note how to adhere to best practices.
Because substructures of this sort are located underground, there is a specific requirement for them to feature smoke outlets that are directly connected to the open air or in some cases to be mechanically vented. This is true for every basement storey, unless its floor area is smaller than 200m2 and is no more than three metres below the adjacent ground level.
The easiest way to do this, as you can imagine, is carve holes into the ceilings of the basement. Unfortunately, though, this isn’t feasible, as it will make walking on the pavement hazardous for pedestrians — we can’t have random gaps in the streets.
That’s where pavement smoke outlets come in. They allow us to comply with the regulations and provide a safe environment in the basement, while avoiding the risk of injury for passersby. These are a requirement where a basement has smoke ventilation that terminates underneath a pavement, as detailed in Approved Document B, Volume 1, section 16.
Pavement light smoke outlets, also known as break-out outlets, are glass vents that are placed strategically on the pavement above a basement. They’re called pavement lights because the material allows sunshine into the basement, practically working as a two-for-one. These vents look just like part of the pavement, however, firefighters can use tools like a hammer or pick-axe to smash the glass when needed, enabling the smoke to leave the basement into the outside world.
If you’re looking for a less invasive type of pavement smoke vent, lift-out panels are very similar in nature to pavement light outlets. However, instead of shattering the glass, rescue personnel simply lift the panels as necessary. The boards can be made of various materials, but glass and concrete are the most common. It goes without saying that if your basement lacks light, glass is your best bet. Regardless, the panels must be easily identifiable, so a small brass plaque is usually attached to them.
When designed and installed correctly, pavement smoke outlets can be incredibly effective at venting smoke out of a basement. However, some considerations have to be made. For example, you shouldn’t place these outlets in locations that would impede people from safely evacuating the building. That’s why they are almost never situated near doorways.
Panels should also be resistant to rain, as water must not enter the building. Other elements that should be thought about when installing these outlets are property usage and footfall, as well as the potential future shrinkage or expansion due to structural movements of properties or the weather.
In 2004, a government literature review regarding firefighting in under-ventilated compartments was released. Drawing on a study for the Department of the Environment by the Fire Research Station, it found that pavement smoke outlets didn’t lead to much improvement in basement ventilation.
However, evidence from the Fire Experimental Unit indicated that, on the contrary, these could have a significant beneficial effect for the firefighting environment. It was also found that, when combined with PPV (Positive Pressure Ventilation) fans to help force the smoke out of these vents, pavement outlets are even more effective.
Based on this information, the Home Office recommended that “the existing provisions for basement ventilation should remain within the revised Approved Documents as an interim measure”. That said, the operation of pavement lights is uncontrolled, so their operation potentially places firefighters in the path of unpredictable fire developments.
If you’re in the process of building or restructuring a basement and require assistance with smoke ventilation, get in touch with us so that our team of experienced experts can help you.