Last Friday, a major fire broke out in student accommodation in Bolton. It was tackled by 200 firefighters and took more than nine hours to put out.
Worse, the fire started in the late evening and, according to media reports, the fire alarm may not have activated correctly. Those who did hear the alarm weren’t sure whether to take it seriously. There had been several false alarms in the recent past.
The top floor of The Cube, which houses students from the University of Bolton, was gutted and damage was caused to the fourth and fifth floors of the six-storey building.
But, thankfully, there were no fatalities, and only two people required medical attention. However, a major source of concern is that the fire spread very quickly.
An investigation has been launched and, while we can’t prejudge that enquiry, once again cladding is to be one focus.
While the cladding was not of the same type as that on Grenfell Tower, initial reports suggest that it did not inhibit the vertical spread of the blaze.
But what is certain is that, whatever the reason, there was a major failure of containment.
Tackling a fire generally involves the removal of heat, in most cases using water to soak up heat generated by the fire.
Without energy in the form of heat, the fire cannot heat unburned fuel to ignition temperature and the fire will eventually go out. In addition, water acts to smother the flames and suffocate the fire.
But what is needed is containment – to prevent the fire spreading from its original location. Those protective barriers are often external curtain walling or internal glass screens. They must also provide escape routes for the building’s occupants.
That’s where fire resistant glass and glazing systems are so important. Modern steel systems are so technically advanced that they have overcome the limitations inherent in the glass itself.
The biggest limitation is that glass softens over a range of 500˚c to 1500˚c. To put that in perspective, a candle flame burns at between 800˚c and 1200˚c. In a flashover blaze inside a building, temperatures can reach between 1000˚c and 1400˚c.
These temperatures can disrupt the integrity of conventional panes of glass, which can crack and break because of thermal shock and temperature differentials across the exposed face. This will compromise the compartmentation of the building’s interior allowing fire to spread from room to room.
That can, incidentally, be a problem that a sprinkler system actually causes. There have been several notable cases where cold water has caused the glass to break and allow more oxygen to the seat of the fire.
To make things worse, due to thermal expansion, flammable gases are able to pass through relatively small holes and gaps in ducts and walls, spreading the fire to other parts of the building. Heat will also be transmitted through internal walls by conduction.
An unchecked fire can spread with devastating speed, as it did in Bolton last week and the best means of survival is usually escape.
When a modern building is designed, assessing risk is the starting point. In particular the need to build in compartmentation throughout the building.
That means looking at the whole building’s capacity to withstand a fire or other threats. For the glazed components, that means analysing the level of containment the glass will provide.
Importantly, that analysis must also examine the compatibility of the glass with its framing system. One is an important at the other. If one fails, the other fails.
To put that into perspective, modern steel systems can deliver 120 minutes of fire resistance. That’s more than enough time to evacuate a building and isolate the blaze.
The Bolton fire is an example of a complete failure of compartmentation. It’s also an example of why containment is so important.