In high-rise fires, we are racing against time

IN a previous column, I wrote about how the World Trade Center tragedy on September 11, 2001, was not merely the story of two skyscrapers collapsing.

It became an enormously costly engineering case study, teaching us about structural robustness, impact damage, loss of fireproofing, multi-storey fires, redundancy and, ultimately, how resilient a building remains when several layers of defence fail simultaneously.

But there is another lesson from the tragedy that is particularly relevant to fire safety engineering and high-rise buildings.

It can be summarised by a simple equation: ASET > RSET.

Behind that equation is something fundamental to survival during a fire: time.

ASET, or Available Safe Egress Time, is the period available before conditions inside a building become unsafe for occupants. RSET, or Required Safe Egress Time, is the time occupants need to recognise an emergency, understand the warning, decide what to do, move towards an exit and eventually reach safety.

Put simply, ASET is how much time the building gives us. RSET is how much time people need to escape.

For occupants to remain safe, ASET must be greater than RSET, with an adequate safety margin between the two.

The events of September 11 illustrate why this matters. After the aircraft struck the World Trade Center towers, structural damage occurred, portions of fireproofing were dislodged, fire protection systems were affected and fires spread across multiple floors. Some evacuation routes were also damaged or severed.

Each failure reduced the amount of time potentially available to occupants. ASET was shrinking.

At the same time, thousands of people needed time to evacuate. People do not immediately appear at the ground floor when an alarm sounds. They must recognise what is happening, understand instructions, decide how to respond, reach the staircases and descend potentially dozens of floors.

Some move quickly while others may have mobility limitations. Some help colleagues. Others hesitate or wonder whether evacuation is really necessary. All these factors contribute to RSET.

High-rise emergencies are further complicated because firefighters are moving in the opposite direction. Occupants descend while firefighters ascend, sometimes sharing portions of the same circulation routes during rescue and firefighting operations.

That is why evacuating a 50- or 70-storey building cannot be approached in the same way as evacuating a two-storey house.

Understanding ASET and RSET also helps us understand why every layer of fire protection exists.

Sprinklers control fire growth. Compartmentation slows the spread of fire and smoke. Smoke-control systems help protect evacuation routes, while structural fire protection allows structural components to retain their load-bearing capacity longer under fire exposure.

These measures increase ASET.

On the other side of the equation, early detection and alarm systems allow occupants to respond sooner. Clear emergency communications reduce hesitation. Protected staircases allow more efficient evacuation, while fire drills and emergency preparedness help people understand what to do.

These measures reduce RSET.

The philosophy is straightforward: extend ASET, shorten RSET and preserve the safety margin between them.

This is particularly relevant to Malaysia, where we sometimes become too comfortable with a checklist mentality.

Sprinklers, wet risers, fire alarms, smoke control, fire doors, protected staircases, emergency power and a Fire Command Centre may all be present. Everything appears to have been provided, so we assume the building is safe.

But we should ask one more question: Will these systems actually perform when they are needed?

A sprinkler system with an unreliable water supply reduces ASET. So does failed smoke control, a fire door wedged open or compartment walls breached by unsealed service penetrations.

An unclear or delayed alarm increases RSET. So do obstructed escape routes, inadequate emergency preparedness and occupants who have never participated in an evacuation drill.

What should concern us most, however, is not necessarily one isolated failure. Buildings have layers of protection and redundancy precisely because individual systems can fail. The greater danger arises when several weaknesses converge during the same emergency.

Imagine unreliable sprinklers, malfunctioning fire doors, compromised compartmentation, problems with smoke control and occupants unfamiliar with emergency procedures.

ASET is shrinking while RSET is expanding. Between them is a rapidly disappearing safety margin. This is why defects discovered during inspections should never be viewed in isolation. 

A defective fire door may appear to be an ordinary maintenance problem, while an unsealed penetration above a ceiling may look minor. Risk-based thinking requires us to ask what each defect does to ASET or RSET and what happens when several failures occur simultaneously.

In a high-rise building, the building itself is the first line of defence.

When a fire breaks out on the 40th floor, firefighters are not there immediately. But detection systems, sprinklers, compartmentation, smoke control, wet risers and protected staircases are already in place.

Before the first fire engine arrives, the building must begin protecting its occupants.

The taller and more complex the building, the more we depend on these built-in layers of protection. That is why maintenance cannot be reduced to fulfilling a contract. Inspections must be more than checklist exercises. Fire drills must be more than calendar obligations. And a Fire Certificate must never be treated as simply another document on the wall.

The mindset must move beyond compliance towards reliability, redundancy and resilience.

Compliance tells us that requirements have been met. Reliability asks whether systems can be trusted to perform when needed. Redundancy ensures that one failure does not become catastrophic. Resilience determines whether a building can continue protecting lives when an emergency does not unfold as expected.

This responsibility does not rest solely with fire and rescue authorities or fire safety professionals. Total fire safety requires all five critical components — authorities, designers, builders, inspectorates and occupants — to understand their roles and work together.

Every stage matters, from planning and design to construction, inspection, maintenance and everyday occupation. A weakness at any point can affect how a building performs when lives are at risk.

If Sarawak can embrace this approach collectively, Sarawakians can help build a stronger and more responsible fire safety culture. Ultimately, safety is a shared responsibility.

And at the heart of it all is the most valuable commodity in a fire: time.

Time to detect, warn, decide and move. Time for sprinklers to control the fire and compartmentation to contain flames and smoke. Time for occupants to evacuate and firefighters to intervene.

Perhaps the most important question arising from September 11 is not simply why the Twin Towers collapsed, but how much time a building can give its occupants when its layers of defence begin failing one by one.

When a real fire occurs, a building will not be judged by the beauty of its approved drawings, the thickness of its maintenance files or the certificate on the wall.

It will be judged by whether its systems perform when lives depend on them.

The formula is simple: ASET > RSET — give people more time than they need to reach safety.

Because in a high-rise fire, we are not merely fighting fire.

We are racing against time.

The views expressed here are those of the writer and do not necessarily represent the views of Sarawak Tribune. The writer can be reached at khirudindrahman@sslborneo.com.my