How safe from fire are high rise buildings?

London’s Grenfell Tower fire shows what can go wrong when a high rise building is not designed or retrofitted in accordance with fire and safety needs. But the fire safety engineer for Wilshire Grand says US towers are generally safe.

The death toll in last week’s Grenfell Tower fire has reached 79 people. The exact cause of the blaze that consumed the retrofitted tower in London’s Borough of Kensington is not yet known — the flammable new cladding has been widely reported along with the lack of sprinklers and exits — but the findings will be closely watched by fire safety experts, designers and builders worldwide.

That includes in Los Angeles where new high-rise towers are under construction, and some older towers are being retrofitted.

Nathan B. Wittasek worked as a firefighter before becoming a fire protection engineer.

But the design of towers differs according to their age and the culture of the country they are in, and the US has a pretty good record of fire safety in high rise buildings, says Nathan B. Wittasek, a former firefighter, and now a fire protection engineer with the firm of Simpson Gumpertz & Heger.

That is because designers have applied lessons learned from past disasters — such as the collapse of the World Trade Center — and developed a “belt and suspenders” approach with multiple redundancies built in.

Wittasek has consulted on the design of many towers including Wilshire Grand, the tallest building in the West scheduled to open this Friday. His office is in the AT&T Center, formerly the Transamerica Building, a 1960s building designed by William Pereira that was renovated by Gensler a few years back.

We talked to him about lessons learned from past fires, the multi-tiered approach that makes towers safer than many low-rise buildings, and the challenges of retrofitting older towers with new technologies and materials.

Nathan B. Wittasek: The first thing to keep in mind about high rises is that they’re actually one of the more safe building types because they have such a large number of features that are designed to both detect and control fires. . . everything from fire pumps, fire detection systems, and in high rises here in Los Angeles we have smoke control systems that are designed specifically to limit how heat and smoke will migrate through the building. Not to mention the backbone of these buildings which is the passive compartmentation.

Because of that, the actual history of high rise buildings is actually quite good with respect to fire and safety. Every once in a while you have an event like what we’ve seen in London and it reminds you that you really have to think about how these features go together. But on the whole we are very fortunate because this country has spent a great deal of time and effort really developing the standards that are used around the world.

DnA: Can you explain passive compartmentation?

NBW: That’s the inherent ability of the building structure — through its floor ceiling membranes, through the floors, the walls in the building including the exterior walls — to resist the spread of fire. And that’s a really important aspect for high rise.

One thing we’ve learned over the years is that you really want to have a belt and suspenders approach on these types of buildings because [fires in] high rise buildings are very challenging to fight simply using manual suppression.

In other words, you really need the systems to help you fight the fires and contain them in these buildings so we rely upon more or less a system of redundant approaches. And one of the most basic approaches is to have walls and floors and ceilings that will resist fire for a certain amount of time.

DnA: And what we saw in London was that the fire spread rapidly between floors. One of the notions that’s being floated is that there was this cladding system that didn’t provide for the compartmentation.

NBW: Correct. That is what we’re hearing at this time. And we don’t know the specifics. As is common we’ll hear quite a number of reports about potential causes and we have to be very careful. What we’ve learned over the years is that very often the first reports, while they are educational, they just represent a part of the story. Now in the case of the fire in London we have quite a lot of anecdotal evidence. We have video evidence, we have a lot of information that points to what looks like clearly an unintended and uncontrolled spread of fire up through the building and we are also hearing that the cladding had something to do with that.

DnA: Can you explain the role that cladding plays?

NBW: In these types of buildings we often have a skin for various reasons, whether it’s energy conservation or just simply the need to have something that’s rather lightweight. You’ve heard probably that the materials are plastic-based or they have a type of foam insulation. And that cladding is often encapsulated with noncombustible materials that are specifically designed to slow the spread of fire.

Now in the United States we have codes that for example will say when you’re above a certain height — say 75 feet — you really have to have automatic sprinklers. It’s a very old type of fire protection but we’ve found that in high rise buildings it really buys us the time and the ability to control the fire whether it originates from within the building or from a source outside.

Cladding can catch on fire, whether or not it’s fire resistive or fire retardant or not. And then what tends to happen is that fire can quickly spread because fire likes to move up and that can spread the entire way up the building if we’re not careful. One of the reasons we have sprinklers is to allow for the interior of the building to remain protected in the event that we have a fire that goes up the exterior of the building, creating potential exposure for the inside.

Wilshire Grand has an exit exclusively for use by firefighters, based on lessons learned from the World Trade Center collapse (photo courtesy Wikicommons)

DnA: So in terms of a checklist of protections you need fire retardant or resistant cladding, sprinkler systems, passive compartmentation and then there’s also the issue of exits? 

NBW: Sure. This is in part a cultural issue. Here in the United States we rely upon multiple exits in these types of buildings. For example, in [Wilshire Grand] we have an additional exit that’s [exclusively] for the use of the firefighters who would be coming up to suppress the fire.

Now in the UK there has been a longstanding history of high rise buildings that have in some cases just a single exit. And this in part goes back to the culture of how they will exit people. Whereas in the United States we tend to self-evacuate, in the UK they will actually stay put. They will stay in place and allow the fire service — or the fire brigade, as they would say — to come in and assist them and evacuate them from the structure. And that’s a cultural difference.

It’s similar to this notion that in a high rise building here in the United States one of the most common things you’ll see is a sign that says in case of fire, do not use elevator. Well, now we’re starting to use systems that that rely upon enhanced elevators for evacuation. And we realize that we can actually evacuate these buildings very safely and as much as 50 percent faster by relying on these technological advances.

DnA: When you talk about the enhanced technologies of the elevators does that mean the elevator shafts themselves are becoming more fireproof?

NBW: Yes, we do have aspects of the design that are specifically intended to keep smoke and heat from entering the elevator shafts. But beyond that we protect these elevator shafts from the effects of water and even from the effects of power loss. So we could simply lose power in the whole neighborhood and these elevator shafts and the elevators within them would remain operational and the fire department could continue to use these elevators to evacuate people safely.

DnA: The Grenfell Tower fire reminds us that there are a whole number of high rises built in the 1960s and 70s that are now being retrofitted and re-clad. What does that entail?

NBW: You raise a very important point and that is that over time we have to consider compatibility issues. When you take a building that was designed in the 1960s or constructed in the ’70s and then you apply modern materials to it you have to be cognizant of how that building system has a system of fire and life safety features that will respond to that new material or new arrangement of materials. And the codes have given us tools to do that both here and in the UK.

But certainly it’s correct to be concerned about a new material that’s of a high level of combustibility that’s being introduced into an old masonry or concrete building type. And that for example is why here in the United States we would typically require the use of fire sprinkler systems to add to the level of safety when these newer, combustible, composite materials are being used.

In the United States we’ve developed a number of standards that have really helped us address the unique aspects of these types of assemblies, whether they’re installed in new construction or in existing towers. We rely a lot on full scale testing, not only upon a code or some prescriptive requirement.

Very often these incidents are moments that allow us to come together as an industry and re-evaluate what we thought was working. I think that with respect to the use of these materials in existing buildings this incident will raise a lot of questions and it will create discussion around the topic of whether or not we’re doing the right thing.

DnA: So among people in your field and the design and building profession in general this incident is going to be a bit of a clarion call?

NBW: It is, in the same way that the World Trade Center [collapse] spurned research and development of new requirements that to this very day are being implemented in some of the buildings that we’re seeing come up in Los Angeles and around the country.

DnA: Like what?

NBW: For example, I mentioned the third stair that we’ve provided in the Wilshire Grand; that was specifically based upon feedback that came out of studies conducted by the National Institute of Standards and Technology where they interviewed firefighters and they learned what some of the challenges were.

We have enhanced radio systems, we have enhanced elevator systems that are all coming out of these studies and discussions with various groups of professionals, code officials and the firefighters themselves.

And so a number of these features have been implemented in our current codes.

We are very much the state of the art and sometimes it adds quite a bit of cost. But I think everyone would argue that in the face of losing your family or losing your own life it really doesn’t make a difference and it’s not such a great cost.

DnA: This awful event in London illustrates how important fire considerations are as part of the design of a building. Generally we don’t talk about it very much except when there’s a massive fire.

NBW: I’m unfortunately one of those people who, wherever I go, I tend to talk about it to my friends. So sometimes I think I fail to get invited to parties for that very reason.

But we have an expectation that buildings, places where we work, especially where we sleep, are supposed to be the safest places that we have in our life. And even though statistics bear out that the chance of losing your life [to fire] is quite small relative to the other types of hazards that we face in our life, the fact remains that there is an expectation that we should be safe in these buildings where we put our children to sleep. And I think that’s why it’s particularly shocking when you hear about a fire and you see the images and hear the stories of how people had to cope with a tremendous tragedy and a threat to that sense of safety.

DnA: What brought you to fire protection engineering?

NBW: I have a structural engineering background, but I also was a firefighter and spent many hours riding in both the front and the back of a truck back in Auburn, Massachusetts. That came together with a real love for architecture and I came out to Los Angeles and saw a way to combine the two and that’s how I ended up doing what I do.

DnA: How would you say your experience as a firefighter informs you?

NBW:  I think the most important thing that I learned was, number one, how fast these fires can evolve and how dangerous they can become in a very short duration. The other thing that came out of the firefighting was just the human component, that there are real faces and I remember the faces of people that were not so fortunate.