A typical apartment building within a jurisdiction is three stories high with eight units on each floor. There is an open, unprotected stairway from the first to the third floor (see floor plan).
How hazardous is this building from the aspect of life safety, property protection, and value to the community?
In most cases, the answer is subjective. It depends on the experience of the fire service manager, the size of the jurisdiction in which the building resides, the regional location of the building in the country, and other factors (such as population density, exposures, accessibility, building construction, water supply, fire loads, etc.).
Every fire department has a fire protection system—whether it’s a good or bad system, however, is another matter. The fire protection system doesn’t eliminate risk, rather, it reduces or minimizes the risk to the public it serves. The system includes all bureaus, divisions, agencies, etc., involved in keeping loss of life and property and the community consequences to a minimum, acceptable level that the community can afford.
In general, the broader your base of interacting agencies, the more successful your fire protection system will become. There must be an interrelationship between what your fire protection system should be accomplishing and the people who should be operating it. By studying your district’s fire protection system and breaking it down into separate components, we can analyze and determine where its strengths and weaknesses lie.
Fire risk analysis, a course developed by the National Fire Academy, gives the fire service manager a simple measurement tool that can be used to objectively measure fire risk, life risk, and the value of a building to the community. Risk analysis allows the fire officer to determine his fire suppression capabilities for a particular building and the unprotected risk within that structure.
The unprotected risk is the difference between the amount of pre-planned resources needed to protect a building minus the actual resources available through the fire protection service assigned.
With risk analysis, the fire service manager is in a position to objectively measure both the fire risk in any building and the suppression capability of his department. This objective data can be used to identify and list the needs of that department; the need to reevaluate fire protection codes; or the need to additionally retrofit fire protection systems in a particular building. As the unprotected risk is eliminated, an accepted risk can actually be determined for a community.
Although the concepts involved are not new, the simplicity of this system and the ease of understanding it are.
FIRE RISK DETERMINATION
Fire risk is determined by calculating two fire flows in gallons per minute on the building, the initial attack flow and the sustained attack flow. These flow determinations act as a yardstick to measure the fire risk within the building and give the incident commander an idea of his department’s fire suppression capabilities and ability to protect target hazards.
Initial attack flow determination can be compared to an offensive interior attack strategy. This determination is made by finding the largest open area within a building where a fire could spread in its initial phase before flashover occurs. This area is calculated in cubic feet. Using our three-story building as an example, we could deduce that the worst case situation would be the involvement of one apartment plus the corridor. Although the fire is still at its original location (in one section of an apartment), the calculated area is charged with smoke and heated gases. To determine the amount of water needed to effectively neutralize this calculated area, the following formula may be used:
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cubic feet of area/100 = gpm needed/ delivered for 30 seconds
In our building illustration, we see that the apartments are 1,200 square feet (40 feet long X 30 feet wide) with 8-foot ceilings; the corridors are 100 feet long, 8 feet wide, and 8 feet high. Therefore:
((1,200 * 8)+(100 * 8 * 8))/100 = gpm/30 sec.
(9,600 + 6,400)/100 =gpm/30 sec.
16,000/100 = gpm/30 sec.
160 = gpm/30 sec.
The initial attack analysis must be calculated before a fire occurs. This fire risk measurement tool can be used for two purposes: as a guide by incident commanders for firefighting purposes, and as a yardstick by fire service managers to determine the fire risk of a particular structure.
The second fire risk measuring tool is the sustained attack flow. If the initial attack flow is not made within about 10 to 15 minutes from the fire’s onset, or if an insufficient initial attack is made, then a sustained attack will be necessary. A sustained attack is a defensive exterior attack provided within 30 minutes of receiving the alarm.
The sustained fire flow is based on the:
- Square footage of the building
- Determined number of stories
- Construction of the building
- Occupancy use
During pre-planning, a fire flow estimate form (see example on opposite page) may be used to determine your department’s sustained attack capabilities. Using the basic information from our Apex Apartment House, most of Block A on the form can be filled in. The fire management area (FMA) is the sector designation of the particular fire protection district involved. By dividing a district into smaller designated areas or sectors, the management of an incident within that district is greatly assisted.
The types of construction of the involved structure need to be identified and included in Block B. The building official of the jurisdiction may have to be consulted to make this determination.
The largest expected fire area is calculated in Block C. Multiplying 70 feet * 160 feet (width * length) will give an area of 11,200 square feet for one floor. Using variable “a” in Block C (add 50% of all other floor areas) because the structure is not constructed of fire resistive materials, an additional total of 11,200 square feet will be added for the other two floors of the building (5,600 square feet for the second floor + 5,600 square feet for the third floor). Adding this figure and the 11,200 square feet for the largest floor area, we get a total of 22,400 total square feet.
The base fire flow (Block D) is determined by the total square footage from Block C and the construction type (Block B) and applying them to the base fire flow table (see table in next column). Looking down the wood frame column on the base fire flow table, you can see that 22,400 is between 20,600 and 23,300. When determining the base fire flow calculation, always choose the larger number. Now, looking horizontally back across the columns to base fire flow, you can see that for a wood frame structure with a total square foot area of 22,400 it is 4,000 gpm. However, this “working figure” will be further adjusted as we work through the form.
Block E allows for fire loading adjustments based on occupancy of the structure. To determine these adjustments, use the table at the bottom of this page.
For residential occupancies, the fire load adjustment factor (15%) is first multiplied by the base fire flow determined in Block D (4,000 gpm) yielding 600 gpm. This 600 gpm is then deducted from the 4,000 gpm basic fire flow, leaving 3,400 gpm as the fire load adjustment factor.
The fire flow for the sustained attack is further influenced by the demands of the surrounding exposures. Block F allows us to determine these needed flow adjustments. Let’s say that our size-up of the Apex Apartment House showed that it has the following exposures:
- North side—one-story office building, 65 feet distance.
- East side—one-story building, 20 feet distance.
- South side—ten-story office building, 55 feet distance.
- West side—two-story residential building, 10 feet distance.
The one-story office building 65 feet to the north of the fire building would require a minimum exposure adjustment of 5%. The one-story building 20 feet to the east of the fire building would be a medium risk exposure and receive an adjustment of 15%. The ten-story office building 55 feet to the south would be a medium risk exposure and receive an adjustment of 15%. The two-story residential building 10 feet to the west would be a very high risk and receive an adjustment of 25%. The total exposure adjustment would total 60%. This percentage is multiplied by the calculated fire load adjustment (3,400 gpm), yielding 2,040 gpm. This figure is then added to the fire load adjustment (2,040 gpm + 3,400 gpm), making the exposure adjustment gpm 5,440.
Block G is a guide for rounding off our calculated figures for flow. Using the chart, we can figure the final sustained fire flow for the Apex Apartment House at 5,500 gpm.
This process is not intended to address buildings protected by automatic sprinkler systems. If a properly designed and maintained sprinkler system is provided, there would be minimal demand for manual fire suppression efforts. Reductions of up to 50% in the determined fire flow have been common practice in many parts of the country.
LIFE RISK ANALYSIS
Life safety is much more dependent on the characteristics of a building and its built-in safety features than on the capabilities of a fire department’s search and rescue operations. To understand all the factors influencing life safety would be to undertake a complex study in building construction, occupancy, human behavior, and built-in fire protection.
In the risk analysis approach, buildings are classified into one of five potential risk levels based on interior or exterior exiting; inadequate exiting; code compliance; the type of auxiliary fire protection provided, i.e., sprinkler systems, automatic fire alarms, detection systems; and manual fire alarms (see life risk matrix).
Another major consideration in life risk analysis is the number of occupants and their ability to safely exit from the building without assistance. The very young or elderly would indicate a higher life risk than other age groups; and those with physical or mental impairments would present a greater risk. Crowded occupancies place more people in danger, increasing the total life risk.
COMMUNITY RISK ANALYSIS
The final risk analysis to be determined for the structure is its value to the community and the consequences of losing that structure due to fire. Community risk is measured from very low to very high (see community risk analysis table) and in terms of the community where the building is located. The community impact will vary depending on the size and character oRhe community. The same type structure fire in two different communities often has vastly different impacts.
Community Risk Analysis
Veg low risk
The community would feel no loss. Damage would be insignificant and localized.
Other than the fire department and those directly involved with the fire, no community impact would be anticipated.
The fire would receive public attention. Some of the people would be temporarily out of work and some tax revenue might be lost.
The entire community would know of the fire. Jobs might be lost permanently and the loss of tax revenue could be significant. A general feeling of remorse would be expected.
Very high risk
The community expresses shock or outrage. The loss of jobs and tax revenue would cause major problems. A major portion of any investigation would seek out “those who allowed this to happen,” Indicators would be large numbers of deaths. jobs lost permanently, bankrupt businesses, etc.
A building that employs 150 people in a small community would have important economic value. Put that building in a large community and its economic value would become less important. The loss of 150 jobs in a large community usually would not cause as significant an impact as it would in a very small community.
Whether a building is occupied predominently by young, old, gifted, or handicapped persons could also affect the value that a community puts on it, as could a building’s historical value. Any building whose loss would emotionally or economically affect most of the inhabitants of the community has a very high community value.
The Apex Apartment House (within these guidelines) would be considered a low risk to the community. However, if it housed handicapped or elderly people, it would be a high risk structure. If Apex was a historical building, it would fall into the very high risk category.
The above information should be entered on a fire risk rating summary form, which will highlight all the necessary building data on one page. This will make filing easier and data retrieval faster, whether the information is stored by a computer, micro-fiche system, or a hard-copy file drawer.
If the incident commander has pre-planned a fire analysis, he now knows what a particular building would require for an initial attack and for a sustained attack. The commander now needs to determine what fire suppression resources (equipment and firefighters) will be needed to meet these suppression demands within specific time frames.
Fire suppression forces are never called in the best of times. So, when the alarm sounds, there has already been some measure of loss. With the ever-present threat of cutbacks in fire service resources and funding, perhaps risk analysis is a way of measuring what the full extent of the loss would be if all of us didn’t show up.