September 11th may have been the worst day we will ever live through. Since then we have poured out our emotions with patriotism in defiance of the terrorists that killed over 3,000 civilians and caused the massive destruction of the World Trade Center.
There were 3 reasons that nobody talks about why so few people died that day.
– The NY Giants had a Monday Night Football Game that ended at 1:00 a.m. the night before.
– It was the first day of school on September 11th for Manhattan, Brooklyn, Queens, Long Island, Staten Island and the Bronx.
– There was a democratic primary election going on that morning in Manhattan where people were voting.
Why did they collapse? We know all about the two planes that struck the WTC 1 & 2. They were 767's with hundreds of gallons of jet fuel that caused the massive fire ball and utter collapse.
As fire protection engineers are we to agree with the FEMA study that said it was REMARKABLE that the buildings stood so long and then collapsed. Remarkable should never be a word used to describe that day, event, or how those buildings performed! It is obviously the easier path to say that the buildings performed as designed. But were the designs flawed? Do you ever wonder what would have happened if the Trade Centers were constructed with reinforced concrete such as the Empire State Building or the Chrysler Building?
Why did the local codes change the construction of buildings from reinforced concrete to protected steel? And was the steel in the Trade Centers really protected? The WTC's were designed to sway ~15 – 25 ft. during windy days. Was the fire proofing designed to withstand that movement? We were told that the WTC was designed to take on the impact of a 707. The 707 was the largest airplane at the time the building was being constructed. Was a fire protection engineer ever consulted during the initial design about the fire that would ensue after the 707 hit the building and the jet fuel poured through the building? Or maybe the 707 was a glider and had no fuel and we didn't have to worry about a fire!
Why did the local codes change the construction of buildings from reinforced concrete or steel encased in concrete columns to protected steel (cementitious fire proofing sprayed on steel columns)? And was the steel in the Trade Centers really protected? The WTC's were designed to sway ~15 – 25 ft. during windy days. Was the fire proofing designed to withstand that movement? We were told that the WTC was designed to take on the impact of a 707. The 707 was the largest airplane at the time the building was being constructed. Was a fire protection engineer ever consulted during the initial design about the fire that would ensue after the 707 hit the building and the jet fuel that would pour through the building? Or maybe the 707 was a glider and had no fuel and we didn't have to worry about a fire!
Lets Go back in History to July 28, 1945 when a US Army B 25 Bomber crashed into the 79th floor of the Empire State Building in 1945 killing 14 people but leaving the building relatively unscathed. (See picture below)
Look at the damage. Look at the thickness of the concrete in the exterior wall and floor. The Boeing 767 planes, which hit the towers on September 11th, were almost fully laden with fuel, which on impact triggered explosions and fire. The architects and engineers claimed when the building was designed it could withstand the force of a Boeing 707; the largest commercial airline at the time the building was erected. The 707 has a take off weight of 258,000 lbs., and can cruise at 615 mph and is 130 ft. x 145 ft. The 767 has a take off weight of 312,000 lbs., and can cruise at 550 mph and is 156 ft. x 159 ft. Bottom line the 767 weighs 21% more and is 32% bigger, but the 707 can fly 65 mph faster. Did the size of the plane make that much of a difference? Probably not.
Now the WTC did not have to conform to the NYC Building Code. They had to conform only to the NY / NJ Port Authority codes. Several building officials have been on record to say that if the building had to conform to the NYC Building Code and not the Port Authority Code it probably wouldn't have been built. It was the lightest weight constructed building in NYC. Most people thought it was a NYC Code Building. It was not! NYC building code includes Local Law 5, which states that sprinklers can be omitted in an area of a building if that area has 2 hour fire rated walls and compartmentalized in 7,500 sq. ft. sections. When the Trade Center was built it was an open landscaped office with each floor being 1 acre (52,000 sq. ft.). The floors were not compartmentalized and not protected by automatic sprinklers.
There are three features that go into the design of a properly protected high-rise building:
3. Preventive Maintenance for the Construction & Protection
Let's start with Construction. Where has all the concrete gone? A steel beam encased in concrete will outlive the use of the building, requires no maintenance and will withstand fire at a much greater rate than a protected steel building.
Each floor on the Trade Center was a metal deck with four inches of concrete per floor supported by 59 tubular metal columns on each side. Each tube had four bolts at upper stories and six bolts at lower stories connecting to the metal deck holding the four inches of concrete. The bolts were not fire proofed. The outer shell was a structural support and the next structural support was all the way on the inside of the building by the core. What happened to all of the columns every 25 ft.? We all know the answer but no one has the guts to stand up to the real estate lobbyists and code consultants and scream. The open landscape office offers more useable space per floor. What a joy to be able to see all the way around a floor without any columns. How about the stairwells in the corners of the floors? "No, you can't put stairwells in the corner of a floor! The CEO needs that space as his corner office." This way on one side of his office he can see up the Hudson River and on the other side of the office he can see the Verrazano Bridge. Let's put the stairwell out of the way so Mr. CEO can have his view. How about putting the stairwells by the elevators in the middle of the building. How does egress effectively work if all the exits are in the same area? What if that is the fire area? Didn't it make sense in older buildings where the egress area was located in the four corners of the building?
What is two hour construction anyway? Would you feel safer walking down 100 flights of stairs in a fire with a double layer of 5/8 inch gypsum board on metal stud walls or concrete block walls? They both have the same fire rating but the gypsum board is cheaper and quicker to install – Cheaper. Are you getting the theme of these new buildings? Around 1970 the real estate lobbyists were able to remove a small yet significant part of the building code, which stated all walls within a stairwell had to withstand 150 psi, which is about the pressure from a hose stream from a fire fighter. This small section was removed and in the early 70's exterior walls of stairwells started to become constructed with two layers of 5/8 inch gypsum board and metal studs. Gone were stairwells that had concrete block walls like in the Empire State Building. Isn't the timing ironic that the WTC was constructed around the time the code was changed? Some say it was changed for the construction of the WTC. Imagine what the code consultants would do if paper mache could have a 2 hour fire rating. Isn't the construction integrity of a stairwell so important for egress issues as well as protecting the sprinkler riser, which is located in most high rise stairwells?
Protection – The only reason the WTC had sprinkler protection installed throughout the buildings was because there was a fire in the 70's and the Port Authority decided after the fire it was a good idea to install it. The decision was a Reactive situation. Of course it is better than being Inactive. What ever happened to Proactive management and engineering! Isn't that the best technique to offer the best form of success over the long term?
Fire protection designs in New York City in most cases are under designed. The standard 0.10 gpm / sq. ft. over the most remote 1,500 sq. ft. is the bare bones minimum design for a Light Hazard occupancy on a well compartmentalized floor. It is the cheapest sprinkler system.
A Light Hazard office occupancy is definitely not your typical NYC office. A light hazard office would include a metal desk, tile floors and minimal combustibles. With all the books, papers, files, wood desks, plastic chairs, carpet etc…. Factory Mutual decided many years ago to design all office occupancies for a 0.15 gpm / sq. ft. over 2,000 sq. ft. based on the open landscape environment. This is based on occupancy classification, Ordinary Hazard Group 1, which suits the combustible loading and the lack of compartmentalization of a typical NYC office. In the late 90's Factory Mutual reassessed their design and determined that a well compartmentalized light hazard office occupancy could be properly protected for 0.10 gpm / sq. ft. over 1,500 sq. ft. design.
General Electric (GE) is an example of a proactive company. Did GE conform to the minimum basics of the NYC codes and go with the 0.10 over 1,500 for all their buildings in NYC including all the Rockefeller buildings at Rockefeller Center? Of course they went above the minimum. GE is quality like everyone knows.
Preventive Maintenance for Construction & Protection is one of our favorite topics. Remember the Meridian Fire in Philadelphia where they had the Italian PRV's that were improperly set? The sprinkler water dribbled out of the sprinklers because the PRV's were choking off all of the water pressure to the floor. Well what about NYC? When was the last time a PRV was tested? Was it set properly? Are there gauges before and after the PRV to check the pressures? No, No, No and No! How do you know if you will have adequate fire protection water for your sprinkler system on the 87th floor of a building? NFPA 25 recommends monthly flow tests of the PRV's. The monthly test should compare the original manufacturer's performance curves with the monthly test to determine if they are operating in a satisfactory manner.
One mile away, as the crow flies, from NYC is Jersey City, NJ. A pump test is conducted for company ABC in NJ on their 40 story building every year according to NFPA 25 guidelines. The results of the test are usually satisfactory because the weekly preventive maintenance on the pump is excellent. ABC Company also has a 40 story building in NYC. In NYC that pump is rarely tested. Fire pumps can be the most important piece of equipment in a building. About 40% of all pump flow tests fail for some reason. The two most important tests are the weekly churn test (automatically starting the pump by pressure drop) and the annual full flow pump test. Why can fire pumps be tested in New Jersey but not in NYC?! NFPA 25 is the Maintenance and Testing Standard for Fire Protection Systems. Most states across the Unites States have adopted the standard as part of the building code. This includes New York State with the exception of New York City! Why? It costs too much money to run fire hoses out of the basement of the building to test the four – six fire pumps in the building each year. Unbelievable but true!
Does fire proofing need a preventive maintenance program? There have been rumors circulating that the fire proofing on the core of the WTC had bare spots exposing the steel. Steel starts to fail and deform at 1,250°F. The fire on 9/11 was not a traditional fire. With the jet fuel being involved, temperatures soared quickly to well over the failure point for exposed steel.
The NYC fire department is the best and bravest in the world. They rushed into the WTC on 9/11 never imagining the buildings would collapse. Their bravery is a testimony to the heart of NYC. What about all of the other high-rise fires in NYC? Several FDNY captains have gone on record stating that a fire above the reach of a ladder truck, which is usually the 10 – 12th floor, would grow uncontrolled to the roof of the building. The only way the fire may be controlled would be an adequately designed sprinkler system, proper reinforced concrete construction and a preventive maintenance program.
A prominent fire protection magazine publication from the Midwest always harps on the fact that more people have died from snakebites in Montana (or somewhere in middle America) than fire in the USA. Looking at the data gathered by NFPA, the statistics over the past 20 years support his statement. Most fire protection engineers would argue that the primary purpose of a sprinkler system in a warehouse or 1 story commercial building would be to protect the assets (building, machinery & equipment) and minimize potential business downtime. It's pretty easy to run out of a 1 story building in a fire. A high-rise building is a totally different scenario. High-rise buildings in NYC can span three football fields up into the clouds. A high-rise in Montana is a 30 ft. high grain silo. At the WTC you were able to see the prop planes fly down the Hudson River at the 100th floor, helicopters at the 80th floor and blimps somewhere in between.
The fire protection community needs to wake up! We need to battle the real estate lobbyists and code consultants so we can offer proper protection, construction and preventative maintenance for high-rise buildings. We need to be proactive. Can we design a building to protect against terrorist acts? Probably not. But a fire in a high-rise building above the reach of the fire department will happen someday and we need to act now to save potential loss of life. Improving protection, construction and preventive maintenance of these systems for high-rise buildings is imperative.
Knowing all of this information about the WTC, do you still think it was "Remarkable" for WTC 2 to collapse in less than 1 hour?
If you have any questions regarding upgrading your high-rise facility please contact Risk Logic.