In a two-part article, Jane Embury looks at a worrying trend among some contractors
Fire and building regulations are there to minimise loss and save lives in the event of fire.
Specifications on the length of time that an advanced glazing system should withstand fire are also there for the same reasons.
We’ve therefore drawn attention several times to what some contractors are doing. Reducing the specification from 60 minutes to 30 minutes.
All perfectly legal, but a specification change for one reason only. To save money, and maximise profit.
In a sense, nothing wrong with that because every company has to make a profit.
But the underlying calculation being made is that serious fire is a rare occurrence. Despite fire costing many lives every year, the calculation is that a serious fire will probably never happen.
That’s how we are able to design steel glazing systems to provide safe evacuation routes in a fire or terrorist incident.
Providing those safe exits remains fundamental to fire and building safety. But human behaviour in an emergency situation can also be an important factor.
And it’s human behaviour that calls into question any reduction from 60 minutes to 30 minutes.
Evacuation models, based on engineering and computational tools, have been used for some time to estimate the time taken to evacuate a building.
These models, particularly for larger or more complex buildings such as hospitals, are a requirement of fire safety and building approval.
But research at the US National Institute of Standards and Technology (NIST), among others, demonstrates that those computer models don’t necessarily reflect the variable nature of human reaction.
Assumptions built into the evacuation model can be either too optimistic or too conservative. These can lead to additional risk or cost.
In other words, computer modelling can only take us so far in designing in safety. What’s needed is recognition of human psychology in an emergency situation.
By understanding that, a fire safety team can develop a more comprehensive – and predictive – behavior model for a building’s evacuation.
In the perfect world of computer modelling a fire alarm sounds in an office building and everyone reacts promptly.
They use only using designated stairways and exits, and make their way outside in a brisk but orderly manner.
But computers can’t take into consideration what’s termed “exit choice behaviour.” That determines the different exits that people will actually choose to leave by. They could simply be entrances and routes by which they arrive at work.
Nor does it model “pre-movement times.” That’s the golden period immediately following a fire alarm. The fire has been detected but doesn’t yet pose a threat.
While occupants should move to an exit, many won’t. Some members of staff will assume that it’s yet another fire alarm test. Or assume that it’s a false alarm, particularly if they’ve happened before.
Others will choose to ignore it because they’re busy, up against a deadline, or have mobility problems. Others might not want to appear fearful in front of colleagues.
Many will not want to move from their desks until they receive some guidance from their boss. They might not get that if their boss is the person who’s busy or up against a deadline.
The psychology at work is that a fire alarm in itself is not necessarily regarded as an immediate call to action. It may be an alarm, but it’s not alarming.
The alarm may have sounded, but no threat is apparent. There is no visible fire and no detectable smoke.
We know that the chances of it being a real fire are remote and, mentally, we are hot-wired to think logically. Reason tells us that the situation is unlikely to be dangerous. Therefore, there is no need to evacuate.
However, even when the alarm is taken seriously, it’s also a source of confusion. After all, the alarm is simply a loud noise. It doesn’t indicate the location of the fire, or how serious it might be.
Psychologically, that confusion also adds to a delayed flight response. Most of us instinctually delay responding to a threatening situation until the danger is well understood. We don’t want to walk into danger.
It adds up to a building evacuation that may be greatly delayed, or patchy in nature. Some occupants will take the fire alarm more seriously than others.
But research indicates that this “pre-movement time” is a more significant evacuation factor than the length of time taken to reach an exit.
In the second part of this article, I’ll look at other aspects of building evacuation.