9. Fire protection measures selection
9.6 Benefit/cost analysis
One of the most common risk-based economic analysis is a benefit/cost analysis. This analysis is calculated using Equation (1):
benefit is the value associated with lost revenue, operation, and building replacements that are avoided if a major fire is prevented (benefit of avoided loss)
cost is the cost to protect against damage due to major fire e(RM) is the effectiveness of remedial measure
LR is the lost revenue (in $) due to fire (lost load × mill rate)
OC is the operating cost associated with manning the station due to fire damage of
supervisory equipment or additional testing and switching costs associated with restoring service
p(F) is the probability of major fire (probability of an outage due to a fire) RC is the replacement cost of facility and equipment lost due to fire RM is the cost of remedial measure
SB is the societal benefit (in $) lost due to customer outages created by fire
Once the potential financial loss due to a fire has been calculated, the designer should input costs and effectiveness of any proposed fire protection measure into the benefit/cost equation and determine the B/C ratio. If the B/C ratio is less than 1, then the provision of the fire protection measure is not an acceptable investment.
Normally, the B/C ratio should be greater than 1 and preferably greater than 2. A B/C ratio of 2 means that the avoided fire loss cost or benefit is twice that of the cost of the fire protection measure. Therefore it is a good investment.
Any fire insurance coverage can also be included in this type of calculation. The insurance premiums can be included as a fire protection cost, and an insurance payout will reduce the fire costs.
It should be noted that insurers will generally reduce the insurance costs for specific types of fire protection installed. Companies should review the possible premium savings with their insurers and factor any savings into the calculation.
Refer to C.6 for additional information and an example calculation.
Annex A (normative)
Additional information to main body clauses
A.1 Purpose
This clause provides additional information to 1.2.
Fire protection measures reduce the fire risks to the public in the vicinity of the substation and to emergency response personnel. These measures can also decrease the risk to operating personnel.
Fire protection should be integral to the planning, design, and operation of substations. In many instances, fire protection is not considered. Too often, fire protection decisions are made after the planning and design of the substation, which can lead to costly changes late in the project.
Although common cause events are considered, substation fires generally have not been considered in assessing the reliability of the electric system. However, substation fire events have occurred, with significant challenges to system reliability.
Careful consideration of the consequences of a substation fire, and alleviating those consequences throughout the planning and design process, will help to mitigate the consequences of a fire in a substation.
Properly designed substation fire protection can minimize the effect of component failure during a fire on overall reliability of the system supply. Having fire protection systems and processes will minimize the asset and revenue losses from any fire.
A.2 Fire hazards
This clause provides additional information to Clause 4.
Identifying fire hazards can be a complex process. The fire hazard analysis process should be used for planned, new, or existing substations to determine the appropriate level of fire protection necessary to mitigate the consequence of fire. The fire hazard analysis process should be done by a team consisting of substation designers, fire protection specialists, and substation operating staff so that all perspectives are included in the process. The probability of fire and potential magnitude of its consequences should be quantified to help justify the need for fire protection. For further information regarding the process for evaluating industrial fire hazards, refer to Chapter 2, “Industrial Fire Hazard Assessment,” of the ANSI/NFPA Industrial Fire Hazards Handbook, 3rd ed. [B46].
Historical information on substation fires can help with fire hazard analysis. There have been a wide range of types and causes of fires experienced in substations. The types of fires are based on the equipment and systems used in the substations. Fires involving dc valves, outdoor or indoor mineral-oil-insulated equipment, mineral-oil-insulated cable, hydrogen-cooled synchronous condensers, or equipment with fluids containing polychlorinated biphenyls (PCBs) are usually well documented. Therefore, these types of equipment are easily recognized as a fire hazard. There are a number of other substation fire types that are not as well documented. Factory Mutual Data Sheets 5-4 [B57], 5-19 [B58], and 5-31 [B59]; NFPA 851;
and CIGRE TF 14.01.04-1999 [B54] provide guidance on these types of fires.
Clause D.6 covers a study done by a major utility of reported substation fires listed by types.
A.3 Fire protection considerations for substation sites
This clause provides additional information to Clause 5 and 6.8.
A fire risk evaluation should be initiated as early in the design process as practical so that, in addition to other applicable codes and/or regulations, the fire prevention and fire protection recommendations of this document may be evaluated in view of the specific considerations regarding design, layout, and anticipated operating requirements. The evaluation should result in a list of recommended fire prevention features to be provided based on acceptable means for separation or control of common and special hazards, the control or elimination of ignition sources, and the suppression of fires.
Fire Safety Decision Trees is a methodology commonly used to determine the most appropriate strategy for fire protection. It can also be applied to the various hazards that are found in electrical substations. Refer to NFPA 550-2012 [B40] for details on how to use this methodology.
A.4 Forested or grassland areas
This clause provides additional information to 5.2.1.
A fall hazard should be carried out on trees and other vertical vegetation around a substation. Fallen trees should be a minimum of 9 m (30 ft) away from all critical substation assets. NFPA 1144-2013 [B44]
provides a method for evaluating this type of hazard under specific site conditions.
A.5 Prevailing winds
This clause provides additional information to 5.4.
Prevailing wind direction data are available from many national weather organizations, local weather stations, national forest organizations, and airports.
The Society of Fire Protection Engineers publishes several documents that present methodologies for calculating the impact of wind-tilted fire plumes. Both the SFPE Handbook [B79] and the SFPE Engineering Guide for Assessing Flame Radiation to External Targets from Pool Fires [B77] provide examples of methodologies.
A.6 Fire emergency response capability
This clause provides additional information to 5.5.
When designing a new substation or changing an existing substation, the substation designer should review the capabilities of the fire service in the area of the station. If no public fire service or fire brigade is available to fight a fire in the station, then the substation designer should not rely on any manual means of fire protection but incorporate other specific safeguards. The designer could look at incorporating specific design measures into the substation design.
If the local fire brigade or fire department can provide manual fire protection services to the substation, then the designer should work with these groups to determine their specific capabilities. The ranges of fire department or fire brigade capabilities can vary considerably.
Large, well-organized fire departments in major cities can provide significant resources in terms of equipment and work force in a short time to deal with a major fire. Rural volunteer fire departments on the
other hand may not have the same level of equipment and personnel to deal with large-scale fires.
Discussions with the fire departments should be held to determine the following:
⎯ The maximum number of personnel the fire department has available
⎯ The type of equipment available such as pumper trucks, tanker trucks, aerial ladder trucks, foam supplies, and other special equipment
⎯ The number and type of equipment and personnel that would be dispatched to a fire at the substation
⎯ The expected response time
The designer could then review probable types of fires (design fires) that would be expected at the substation and work with the emergency services to determine whether they have sufficient resources to deal with a specific incident. If the local fire department does not have sufficient resources to deal with the design fires at the station, then the designer should work with the local fire department and determine whether there are adjacent fire departments or fire resources that could be used during an incident. Several high-profile substation fires have been successfully suppressed using crash rescue firefighting vehicles from adjacent airports. If such resources are not available, then consideration should be given to including increased substation fire protection features or the possible purchase of required resources for the local fire department.
If the substation designer finds that the local fire emergency resources and water supply are inadequate for manual firefighting, then passive or active automatic fire protection measures should be considered as part of the overall substation fire protection scheme. Some examples of passive measures that could be used in the substation design are providing adequate spacing between oil-filled equipment, provision of firewalls between closely spaced equipment, the use of noncombustible construction for the control building, and the provision of stone-filled pits or other oil containment means around all oil-filled equipment. Possible active automatic fire protection measures include water spray, sprinkler, and inert gas systems.
Fire department personnel responding to substation fires can be exposed to significant fire and electrical safety hazards that they may not be trained to deal with. The types of fire hazards found in indoor and outdoor substations are significantly different from the typical hazards to which public firefighters are normally exposed. As such, they may be putting their own safety at risk.
The most significant hazards that fire department personnel are exposed to are the electrical safety hazards of the substation. Fire department personnel are trained to take an active role and aggressively suppress fires. In the case of a fire in an electrical substation, there may be long delays until substation operating personnel can arrive onsite and make the station electrically safe. In some cases, it may take up to an hour for operating personnel to arrive onsite to make the station electrically safe. Therefore, the fire department personnel want to enter the facility and suppress the fire, before it is safe to do so.
Delays of this type create additional pressures on the responding fire departments because they are concerned that while they are waiting to gain access to the substation fire, they cannot respond to other alarms received. These tensions can create situations where responding personnel take serious risks of electrical contacts and exposures.
The type of equipment and facilities found in the substation are foreign to most of the operating environments to which the fire department personnel are exposed. Therefore, the installation of fire protection in a substation will help control or suppress fires and allow the fire department to access the facility safely.
A.7 Available firefighting water supplies This clause provides additional information to 5.6.
In the event of a fire in the station buildings or mineral-oil-insulated equipment, water is the most commonly used fire extinguishing agent both directly and as part of fire extinguishing agent mixtures such as foam. As part of the design process, the available firefighting water supplies should be reviewed for any station that has a responding fire department or fire brigade. If there is no responding fire department or fire brigade, then the designer may incorporate passive measures (i.e., greater spacing of mineral-oil-insulated electrical equipment) into the station’s design.
The designer should also determine the requirement for firefighting water supplies, based on governing codes, regulations, and bylaws. The following are some of the common standards for firefighting water supplies:
a) Piped municipal supplies
1) Fire Underwriter Survey Water Supply requirements guide 2) Insurance Advisory Organization
3) American Water Works Association b) Rural water supplies
1) ANSI/NFPA 1142-2012 [B43]
2) Various NFPA fire protection application standards such as ANSI/NFPA 13-2011 [B14], ANSI/NFPA 14-2010 [B15], ANSI/NFPA 15-2012 [B16], and ANSI/NFPA 24-2013 [B21]
During the water supply review, the substation designer should look at all possible sources of water adjacent to the station such as lakes, streams and rivers, swamps, and so on. The designer should also be cognizant of the relatively large quantity of water required for multiple hours of firefighting during major substation fires, such as fully involved mineral-oil-insulated transformer fires.
If there is an insufficient water supply available for manual firefighting, then the designer should work with the local fire department to determine whether they have adequate tanker capabilities to bring water to the substation during the fire.
Where a local municipal water supply is not available, responding fire department personnel should be consulted on their needs for fighting all probable fire scenarios. Water tanker trucks, onsite water storage tanks, ponds, lakes, and streams are all possible sources of firefighting water. Passive fire protection measures such as containment, spatial separation, and/or fire barriers are of particular importance where sufficient firefighting water may not be available.
Hydrant systems intended for use by fire department personnel should have suitable grounding clamps and cables available within the station to ground any firefighting vehicles operating within the station.
If the substation designer finds that the local fire emergency resources and water supply are inadequate for manual firefighting, then passive or active automatic fire protection should be considered. Some examples of passive measures that could be used in the substation design are providing adequate spacing between oil-filled equipment, provision of firewalls between closely spaced equipment, the use of noncombustible construction for the control building, and the provision of stone ground cover adjacent to all oil-filled equipment.
A.8 Emergency access to the substation This clause provides additional information to 5.7.
When the substation designer is laying out the station or changing an existing station, he or she may consider emergency vehicle access to all major buildings or major banks of oil-insulated equipment.
In most cases, the normal operating access for bucket trucks and crane trucks will be quite similar to that required by the emergency services. Normally, fire department vehicles do not need to get within 150 m (500 ft) of major risk areas. If the distances are greater than 150 m (500 ft), then consideration should be made to ensuring adequate access is available.
When laying out the overall site plan, the designer should make provisions for emergency access at a minimum of two locations around the switchyard.
Typically, the emergency services vehicles require access roads with a minimum width of 6.1 m (20 ft), centerline minimum turning radius of 12 m (40 ft), overhead clearances of 5 m, and roadbeds that will support the expected load imposed by firefighting vehicles in the various seasonal conditions.
The access points to the station should have a minimum width of 6.1 m (20 ft). These access points should not be located should beneath overhead power lines or adjacent to critical fire hazards that could cause them to be blocked during an incident. The access points should also be remotely located such that the minimum distance between them is no less than 1/2 the overall diagonal distance of the switchyard.
If the access roads throughout the station yard are dead-ended, then provision should be made for a suitable turnaround facility.
A.9 Substation buildings
This clause provides additional information to 6.2 through 6.5 and 7.2.3.
The types of fires created by mineral-oil-insulated equipment or cable can create catastrophic risks to indoor substations. The application of these types of equipment should be analyzed using fire performance-based methods because guidelines may not recommend suitable levels of fire protection for indoor substations. A performance-based method will be able to model more accurately the fire conditions and the impacts to the building occupants, the structure, and other equipment.
The fire conditions can be reviewed based on some of the following types of criteria:
⎯ The blast pressure created by an explosion and the ability of the building to withstand the blast pressures
⎯ The heat release rate and flame height of the fire
⎯ The activation time for fire detection devices and fire protection systems and the ability of fire protection systems (i.e., sprinklers or water spray systems) to suppress the fire
⎯ The available safe egress time for building occupants (including detection time, egress time, and smoke exposure time)
⎯ Volume of smoke being released during the fire
⎯ The temperature exposure conditions of building structural elements and predicted failure time
⎯ Time to allow the fire to burn out
⎯ Fire conditions that the fire department will be exposed to
⎯ Smoke and fire damage to other areas and equipment of the substation
The various performance fire modeling (zone or computational fluid dynamics) techniques provide varying degrees of fire details and simulation results. For an indoor mineral-oil-insulated transformer, target criteria can be as simple as preventing a fire from taking out of service a second transformer, or it can be as complex as radiant heat flux to the building structure or carbon monoxide exposures to building occupants.
The following are some of the recognized performance-based fire safety and protection documents that can be used for a performance-based analysis:
⎯ SFPE Engineering Guide to Performance-Based Fire Protection [B78]
⎯ SFPE Handbook of Fire Protection Engineering [B79]
⎯ British Standards Institute, Fire Safety Engineering in buildings (Part 1 Guide to the application of fire safety engineering principles) [B51]
⎯ Australian Building Codes Board, Fire Safety Engineering Guidelines [B49]
⎯ The Canadian National Building Code (objective-based) [B73]
⎯ AICHE Guidelines for Chemical Process Quantitative Risk Analysis [B2]
⎯ EPRI TR-100443-1992 [B56]
⎯ U.S. Nuclear Regulatory Commission (NUREG) documents A.10 Construction
This clause provides additional information to 6.6.
See NFPA 850 for further discussion on construction requirements. When exploring the additional information available in NFPA 850, keep in mind that the information and requirements presented may be overly conservative for direct application to substations because they are developed for generation facilities, which involve different hazards and threats.
A.11 Fire separation
This clause provides additional information to 6.6.2.
Fire separations are a form of compartmentalization to limit fire spread by isolating a room or space containing a fire hazard. The fire separation compartment will be formed by fire-rated assemblies of the floor, walls, and ceiling of the room. In the absence of applicable building code requirements, the following are suggested fire-resistance ratings for separating substation areas from one another:
⎯ Control rooms, 2 h
⎯ Battery rooms, 2 h
⎯ Switchgear rooms, 2 h
⎯ Cable spreading rooms or tunnels, 2 h
⎯ Telecommunications rooms, 2 h
⎯ Shops, 2 h
⎯ Offices, 2 h
⎯ Warehouse areas, 2 h
⎯ Emergency diesel generator, 2 h
⎯ Flammable and combustible storage, 2 h
⎯ Transformer vaults, 3 h7
⎯ Indoor oil circuit breaker vaults, 3 h (see footnote 7) A.12 Floor and roof
This clause provides additional information to 6.6.3.
ANSI/NFPA 256-2003 [B38] outlines a method to measure the relative fire characteristics of roof coverings. Class A (ANSI/NFPA 256-2003 [B38]) rated roof coverings are effective against severe test exposure, which give a high degree of fire protection to the roof deck, which do not slip from position, and which do not present a flying brand hazard.
A.13 Building openings
This clause provides additional information to 6.6.6.
Most building codes permit opening protective systems (rated doors, windows, and shutter assemblies) to have a slightly reduced rating due to the fact that combustible loading is typically substantially less in front of openings when they are used as functional attributes of a compartment (windows for viewing or doors
Most building codes permit opening protective systems (rated doors, windows, and shutter assemblies) to have a slightly reduced rating due to the fact that combustible loading is typically substantially less in front of openings when they are used as functional attributes of a compartment (windows for viewing or doors