Jane Embury’s second article on learning containment lessons
In my last article I described a 2004 fire in Paraguay. In that tragic fire hundreds died because of a lack of containment and adequate escape routes.
But sometimes we can learn about the dynamics of fire from a residential context. The second fire I’d like to look at is a well-documented fire that took place in Washington DC in 1999.
It again underlines the importance of compartmentation in a fire situation.
At the centre of the tragedy was the House of Pain, the fire station for Engine Company 10 and Truck Company 13.
Theirs is the busiest fire station in the United States, serving a large residential area in the northeast of the city. It gained its nickname in 1991, when fire crews were called out 9,947 times.
Early on May 30th, the District of Columbia Fire and Emergency Medical Services Communications Center received a 911 telephone call. This reported a fire at 3150 Cherry Road.
The residents of the property had been woken by their smoke alarm. They had gone downstairs to the first floor, and found smoke and heat. Wisely, they left the house through the front door, leaving the front door open.
After arriving, and within two minutes, the front window on the first floor was taken out by the fire fighters. This was to provide additional ventilation. The window was removed from the inside, due to obstructions from security bars on the outside. Fire fighters also opened windows on the second storey at the front of the house.
Another fire team positioned by sliding glass doors at the basement level reported that the basement was full of smoke. However, there seemed to be very little fire. A decision was taken to break out the basement’s sliding glass doors.
This was achieved in two stages. First the right half was removed, then the left side approximately 20 seconds later. Once again, there were obstructions from security bars. After the sliding glass doors were broken out, fire fighters entered the basement to conduct a search.
They reported that there were a number of small fires on the floor of the basement. However, these rapidly increased in size after the sliding glass door was opened. The fire fighters were ordered out of the basement as the fire quickly intensified.
Luckily, the team saw a tunnel through the smoke and it was that safe pathway that allowed them to find their way out of the basement. The fire quickly became a fully-fledged inferno. Seconds later, from upstairs, came the first report of a fire fighter down.
It was worse. District of Columbia Fire Fighter Anthony Phillips was pronounced dead on arrival at hospital. He became the 96th fire fighter to die in the line of duty. F/F Louis Mathews, the 97th, died the following day as a result of his injuries. This was the first double line-of-duty deaths in almost 90 years for the city’s fire service.
Two other fire fighters sustained minor injuries but a third, Fire Sergeant Joe Morgan, spent 180 days in hospital. He underwent over 21 surgical procedures for 60% burns.
It was the very routine nature of the fire and its tragic outcome that prompted the District of Columbia Fire and Emergency Medical Services Department Reconstruction Committee to request a full investigation into the fire dynamics of the incident.
This was carried out by the Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology (NIST). Their mission is to conduct basic and applied fire research, including fire investigations. This is aimed at better understanding fundamental fire behaviour to reduce loss of life.
The investigation made use of the NIST Fire Dynamics Simulator (FDS). This is a computer modelling programme that looked at data from three sources. The District of Columbia Fire and Emergency Medical Services Department Reconstruction Committee, and photographs and measurements taken by NIST staff. It also looked at material properties taken from the FDS database.
The investigating team wanted to know how the opening of windows and doors had affected the dynamics of the fire. By using sophisticated modelling techniques, the investigators were able to run different scenarios and see different computer predictions. They could then match what the simulator showed with information they had collected from the scene and from witnesses.
Next, investigators identified what is referred to as the fuel package or fuel load that was involved in the fire. In other words, the total quantity of combustible contents in the space. NIST’s simulator was then plugged into a database of the heat release rates of different types of furniture and furnishings. This is expressed as British Thermal Units (BTUs) or Kilowatts (kW) per second.
The model divided the space involved in the fire into thousands of “cells.” In the Cherry Road simulations, the cells measured just eight inches by four inches high. Once the physical data was entered into the computer, it was able to model the conditions for each cell. It then combined them together to provide an overall simulation of the fire.
Investigators determined that the fire started near an electrical fixture in the ceiling of the basement. The actual fire may have taken several hours to develop to a flaming stage. As the fire spread from the ignition source, first along the ceiling and then to other items in the basement, it first developed quickly but then depleted the supply of oxygen necessary for combustion.
This lack of oxygen had the effect of rapidly decreasing the heat release rate or energy being produced by the fire. It was at this point, when the fire’s heat release rate was being constrained, that fire fighters made their entry on the first floor of the building.
However, and against some expectations, opening windows on the front of the townhouse on the first and second floors seemed to have had no noticeable impact on the fire development.
It was the breaking open of the basement door that created the firestorm. The FDS calculations were that the opening of the basement sliding glass doors provided outside air into a pre-heated but under ventilated fire compartment. This then developed into a post-flashover fire within 60 seconds.
Some of the resulting fire gases flowed up the basement stairwell with a high velocity. They collected in a pre-heated, oxygen depleted first floor living room with limited ventilation.
More precisely, the model showed that the superheated gases moved up the stairs at approximately 18 miles per hour. As the townhouse was only 33 feet high, it meant that the hot gases moved through the townhouse in less than two seconds.
What makes the Cherry Road fire so important is that it was a catastrophic fire that took place in a relatively small area. Its fire dynamics were capable of analysis, using techniques at the forefront of forensic science. Two facts were immediately clear.
First, it underlined how a relatively insignificant fire can become an inferno in a matter of seconds. When it does, flashover can engulf a whole building in a few moments. Many of the lessons of the Cherry Road fire are now part of US fire training programmes.
Second, the inferno was caused by breaking open the compartment within which the fire was contained. In other words fatally compromising compartmentation.
The main lesson for designers is to look at the whole building’s capacity to withstand a fire. For the glazed components, that should mean analysing the level of containment the glass will provide and its compatibility with its framing system.
In many instances, untested combinations of glass and frame are specified separately. However, in a fire situation, the glass will only be as good as its framing system, and vice versa. Insisting on tested, and therefore proven, compatibility, and specifying it as a requirement of the tendering process, should be a matter of course.
As the Cherry Road fire showed, failure to contain fire can have very human consequences. In larger multi-storey buildings, the stakes are higher, and the responsibility on the designer much greater.
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