“If I had asked people what they wanted, they’d have said a faster horse.” — Henry Ford
Today’s firefighters face many challenges that had not previously been on the fire service’s radar, including:
- Residential structure fires burn 800 percent faster than legacy homes built before 1970 (when lightweight construction materials first came into widespread use).
- Those same fires produce more heat and more toxic smoke – smoke that’s laden with toxic chemicals, chemical compounds and carcinogens – than legacy homes, due to the widespread use of synthetic materials and fibers – many of which are petrochemical-based – for everything from the sheetrock and beyond.
- A growing body of knowledge links firefighter exposures to that toxic smoke with a much greater risk of developing cancer than that of the public.
- Water is becoming a valuable commodity in many communities, especially in western U.S. states due to ongoing drought, and increased housing and business development. Rapid extinguishment, using less water, has become a critical component of the fire suppression strategy for many fire departments.
- Better building and fire codes have significantly reduced the threat of a major conflagration (other than wildfire) for many communities. Yet many of the fire departments protecting those communities still cling to the concept of “massive force” when it comes to fire suppression (e.g., 1000 to 1500 GPM pumps on fire apparatus carrying 1000 gallons of water or more responding to residential and light commercial structure fires where the water used to effect fire suppression is typically less than a couple hundred gallons.
Better options for fire suppression pumps
The idea that water is not a perfect tool for fire extinguishment has been long noted, as by former fire chief and fire protection SME, W. E. Clark; “The process of extinguishing fire by water is cumbersome and generally costly … the cost of installing water mains large enough for required flow; the installation and maintenance of fire hydrants; and the acquisition and maintenance of fire department pumpers, fire hose and nozzles, make water a fairly expensive extinguishing agent … the use of water is hardly the ideal way to extinguish fire … there must be a better method waiting to be discovered.”
CAFS
The first recognized compressed air foam systems (CAFS) was developed by a Texas Forest Service employee in the mid-1970s. That employee, Mark Cummins, developed a water expansion system to make better use of available water for fighting wildfires. The system developed by Cummins – which became known as CAFS – received U.S. Patent No. 4318443 in 1982.
Ultra-high-pressure fire pumps
A conventional low-pressure fire apparatus pump delivers between 20 gpm and 2000 gpm at discharge pressures that range from 120 psi to 300 psi. NFPA 1901: Standard for Automotive Fire Apparatus defines ultra-high-pressure pumps (UHP) as those pumps that have a minimum rated capacity of 6 gpm (25 L/min) and that have a rated discharge pressure greater than or equal to 1100 psi (7600 kPa).
The UHP pump produces incredibly small water droplets with four times the surface area of water droplets found in fire streams produced by conventional low-pressure fire pumps. And smaller sized water droplets – because smaller is better in this case –convert to steam more quickly.
When firefighters use a UHP pump, 90 percent of the water either arrives at the burning fuel or converts to steam. And as we know from basic fire science classes, steam conversion is the critical factor in using water for fire suppression. Steam is what takes energy out of a fire, while at the same time, displacing the oxygen the fire needs to continue burning.
Testing various fire suppression agents and delivery systems
The National Defence and the Canadian Armed Forces engaged the services of Canada’s National Research Council (NRC) to evaluate the effectiveness of commonly available fire suppression agents and technology. The NRC conducted fire suppression tests using a variety of agents and pump technologies: plain water, water with foam solution, CAF and UHP.
Researchers built test compartments using wood stud walls and gypsum wallboard for interior wall coverings to represent a residential or small business space. Each test “room” measured 14 ft. (4.26 m) by 12 ft. (3.65 m) with an 8 ft (2.44 m) ceiling height. The total volume for each room was 1,344 cu./ft. (38 m3).
To better represent a residential or small business space, each room had an access door with a dimension of 3 ft. (0.86 m) x 6 ft. 8 in. (2.03 m), with a short corridor (hallway), measuring 7.5 ft. (2.3 m) wide and 12 ft. (3.65 m) long, just outside of the door. The purpose of this corridor was to provide a more realistic fire behavior scenario since residential rooms or business offices usually have a corridor outside the door.
During the test fires, this corridor also acted as a target area for measuring the migration of smoke, fire gases and heat from the fire room to other parts of the building during the fire tests.
Each test space had an identical fire load consisting of two wood cribs, a mock-up sofa and several OSB boards, that were used to line the lower half of the compartment walls. Each wood crib was constructed with 48 pieces of 1.5 in. (3.8 cm) x 3.5 inch (9 cm) x 31.5 in. (80 cm) pine studs, which would produce a 3.5 million BTU (1 MW) fire.
Fire burn test procedures
For each test, the data collection system was activated at time zero. After 45 seconds of data system activation, two wood cribs were ignited using four small pans containing methyl hydrate located underneath the cribs.
Approximately 3 minutes from the ignition of the wood crib, flashover occurred in the compartment and the mock-up sofa and lower wall and floor of the compartment caught fire. At this point, flames were coming out of the compartment through the upper portion of the doorway. Approximately two minutes was given beyond the flashover point to allow development of a deep-seated wood crib fire and an intense fire in the compartment.
A firefighter then initiated fire attack using CAFS, medium pressure water (MPW) or UHP applications. A total of 16 fire tests were conducted using identical test compartments and procedures.
Legacy fire pressure test results
Both CAFS and UHP provided more effective and efficient fire suppression capabilities than that of the legacy low pressure fire pumps on today’s fire apparatus as shown in Table 1 (MPW represents medium pressure water only).
The firefighter provided a hand signal when the fire was knocked down; the time and the amount of water used to that point was recorded. When complete fire extinguishment was achieved, the time and total amount of water used for fire suppression were recorded and the data system was turned off.
Efficient, effective tools for fire suppression
The days are numbered for the conventional low-pressure pump found on most fire apparatus today. Both CAFS and UHP pumps are more efficient and effective tools for fire suppression. Beyond that, they can be force multipliers that provide fire departments struggling with reduced staffing with big time fire suppression capability.
