In everyday parlance, people speak of risks, taking risks, unnecessary risks, and avoiding risks. Certainly, a layman’s definition of risk is widely accepted. But, what about in fire suppression and special hazard applications? Risk has a discrete definition in fire protection engineering, as:
Risk = (Probability of Fire) x (Consequence of Fire)
Probability is expressed in dimensionless units, as one fire in fifty years can be expected; therefore, the yearly probability of a fire is 1/50, 0.02, or a 2% chance of fire in any given year. The probability of fires can be estimated using historical data, the potential hazards involved, and the given use or purpose of the special application being considered.
Consequence can be expressed in several units, but is most commonly expressed in financial damages, or dollars. Consequence can also be expressed by number of fatalities, number of days of lost work, or a higher risk to another system or group of people. Considering the last example, an engine fire within a naval vessel could result in the vessel being immobilized for several days, which would expose the vessel and its occupants to a higher risk of attack or a risk of compromising the mission of the fleet.
Here is an example of several high risk applications that are normally good candidates for fire suppression:
1. Main Switchboard Room in Marine Applications
2. Motor Control Rooms in Buildings
3. Remote Pump House Buildings
The first hazard is risky because main switchboards control high voltage electricity that may arc or fault in such a way to cause a hazard. Also, the conductors may become overloaded and may overheat, resulting in a fire. Thus, there is a recognizable probability of fire. Next, the consequence of an unprotected fire in the main switchboard room is high, because the main switchboard room supplies the main power for the ship. Without main power, the ship would lose all electricity in the ship that is not powered by a back up generator, or, in some cases, all electrical power. This lack of electricity would cause critical navigational systems and communication systems to fail, which would put the ship at an even higher risk of damage by severe weather or other ships. Expressing consequence in dollars, and estimating the probability of fire as once in 30 years, a calculation of risk can be obtained. This risk can be compared to the life cycle cost of a fire suppression system, and can be given as a justification for purchasing the fire suppression system:
Probability = 1/30 = 0.0333 per year
Consequence = $10,000,000 per occurrence
Risk = (1/30) x ($10,000,000) = $333,333.33 per year
This risk is understated because it only factors in the cost of repairing the switchgear and not the danger of having an unpowered vessel.
The relative risk of having the switchgear protected by fire suppression can also be estimated:
Probability = 1/30 (the presence of a fire suppression system does not make it less likely to happen)
Consequence = $100,000 (the damage from a fire and its clean up is much less with a fire suppression system than without)
Risk = $3,333.33 per year
The difference in risk is the value of the fire suppression system, $330,000 per year. If the life cycle cost of a fire suppression system is less than this, it should be installed. Again, only the damage to the ship was factored into the consequence of this risk analysis, as it cannot be easily quantified. However, all consequences of a potential risk should be considered in making risk management decisions.
Motor control rooms and remote pump houses present similar risks; however, they are lower than marine risks. Marine risks, in general, are higher than those of land, because, at land, there are emergency responders available to assist with fire emergencies. At sea, this is not the case, and a fire within a ship is one of its biggest hazards.
The risk of a motor control room experiencing a fire at land would be based on what motors are being controlled within those rooms. In other words, the more important the motor, the higher the fire risk. If a motor control room was controlling and powering the motor of a fire pump, then its loss would represent a general loss of fire protection to the facility being served by the fire pump.
The probability element of the motor control room experiencing a fire that contributes to the highest consequence would actually be lower than the first example, because an initial fire would have to develop in either the control room or the building, and then a fire would have to develop in either the control room or the building. In other words, there would be a need for general fire protection that is supplied by the fire pump, and the motor control room would simultaneously be on fire, unable to provide the necessary fire protection. For two independent events, the total probability is the product of the individual probabilities:
Probability of Dual Fires = (Probability of General Fire) x (Probability of Motor Control Room Fire)
Probability of Dual Fires = (1/50 per year) x (1/50 per year) = 0.0004 per year
Consequence = Total Building Loss + Potential Loss of Life = $10,000,000 + potential fatalities
Risk = 0.0004 x 10,000,000 = $4,000 per year + potential fatalities
While the risk dollar amount is low, expressing the lower probability of the risk event, the chance of fatalities would direct the owner to install fire suppression within the motor control room.
The risk analysis for the remote pump house is similar to those presented above; however, its specificity would depend on the purpose of the pump house, the fluids it is pumping, For example, pumps that are supplying a city with potable water would be considered high risk, because, without them, the residents of the city would be without potable water. For that reason alone, they should be protected with fire suppression, as a fire would represent a health hazard or crisis.