It may seem counterintuitive, but fire can be a serious danger in hydropower plants. In some respects, the danger is even greater than in thermal power stations. Most U.S. hydro plants are 30 to 70 years old but can deliver another 20 or 30 years of service with upgrades — including state-of-the-art fire protection systems. The design options outlined here also apply in large part to other generating stations.
Unlike fossil fuel – powered generating stations, hydroelectric projects consume a noncombustible "fuel" that also happens to be the most common and effective fire suppression agent — water (Figure 1). Our favorite fire suppression agent may be readily available in unlimited quantities, and often already under pressure, but don’t let that fact lull you into believing that hydroelectric stations are "fireproof."
1. One of a kind. An aerial photo shows the Wells hydrocombine dam, owned and operated by PUD #1 of Douglas County, located on the Columbia River in the state of Washington.The first unit began commercial service in 1967. The generating units, spillways, switchyard, and fish passage facilities are combined in a single structure, or hydrocombine. Courtesy: PUD #1 of Douglas County, Wash.
It is true that hydro plants have perhaps the lowest fire risk among electric generating facilities, but that’s only because, generally speaking, the likelihood of a fire is lower than in a fossil-fueled power station. Hydro plants are not without fire risk, and history reminds us that large-loss fires have occurred (see table).
Sample of large-loss fires at hydroelectric generating facilities. Source:Starr Technical Risks Agency Inc.
Hydroelectric stations share many of the same fire hazards as their fossil-fueled cousins and, thus, share many of the same equipment and personnel policies. For example, common hazards include oil-filled transformers, electrical cables and switchgear, air-cooled generators, and large quantities of combustible hydraulic oil. Common fire hazards include hot work, smoking, general storage, and temporary construction/overhaul materials.
What differentiates hydro facilities from thermal power plants is that hydro plants are typically an underground/underwater windowless structure. In many ways, a hydro plant poses more extreme safety issues and rescue risks because of limited building access, lack of natural lighting, and embedded structures — all of which increase the potential of trapping workers on a lower level by a fire on a higher level.
The purpose of this article is to present the design basics of state-of-the-art fire protection systems for both life safety and equipment protection in a modernized hydroelectric facility. Many of the design approaches described also apply to other power generation facilities, so much of the discussion should be interesting to operators of a wide range of power plants. Many design options are clearly delineated in industry design standards, although several gray areas remain.
Life Safety Comes First
The number and type of life safety fire protection features at a facility — both active (such as fire alarms or fire suppression) and passive (including compartmentation or stairwells) — vary widely and normally depend on who designed the plant years ago and the design standards that were in place when the plant was originally constructed. However, the life safety design requirements for all structures share the same goal: Get the occupants out of the building in a safe and orderly fashion in case of emergency before conditions in the building become dangerous.
National Fire Protection Association (NFPA) 101 Life Safety Code (LSC) is the most comprehensive fire protection standard published and the foundation of egress and safety requirements in model building codes. The Occupational Safety and Health Administration generally recognizes compliance with the 2000 edition of the LSC and other applicable NFPA standards as sufficient to meet its General Duty Clause, which requires employers to "furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees."
The LSC has a similar requirement applicable to the protection of fire hazards at hydroelectric facilities: "Every water-surrounded structure... shall have automatic, manual, or other protection that is appropriate to the particular hazard and that is designed to minimize danger to occupants in case of fire or other emergency."
Note that the LSC applies to both new and existing facilities, although the requirements for older, existing facilities are in some sections less restrictive. These two key code provisions guide much of the fire protection design or modernization of a hydroelectric powerhouse.
A life safety evaluation of a facility is a relatively complex project that requires one or more fire protection professionals with specialized knowledge, and this article isn’t a substitute for such expertise. However, there are several key design issues you should have knowledge of if you are involved in the refurbishment of a hydroelectric plant.
Exit and Maximum Distances. The LSC gives requirements on exit, maximum travel distance, maximum common path of travel, and maximum dead-end corridor distance. An exit is more than just a door out of the powerhouse; it’s also an entrance to a space within the building where occupants are supposed to be "safe" until they are able to leave the building. For most powerhouses, this is one or more suitably enclosed stair towers that lead occupants outside the building.
The maximum travel distance is the actual distance that a person must walk from the most remote portion of the plant to reach the exit. The LSC does assume that the occupant is in the same compartment as the fire and must get to an exit. This distance is not always a straight line. The common path is the portion of exit access that must be traversed before two separate and distinct exit path options become available: If one exit is blocked, an alternate choice of exits must be available while minimizing exposure to the fire.
A travel path dead end occurs in a corridor when that corridor continues past an exit, creating a pocket with no escape path except by retracing steps. Common paths and dead-end distances are always less than the maximum travel distance. For example, in a typical hydro powerhouse, the maximum travel distance is 300 feet, the common path is 50 feet, and a dead end is 50 feet.
Escape Stairs. Unless an exit can be accessed within the permitted common path distance, at least two means of egress must be provided from every plant level with at least one exit reachable without going through another level. The LSC permits fire escape ladders and alternating tread devices as means of egress. If the powerhouse has a level located more than 30 feet below the lowest level of exit discharge (that is, a safe location outside the building), or has more than one level located below the lowest level of exit discharge, exits must be of fire-rated construction.
Powerhouses, other than small ones with only one or two levels, generally require two enclosed stair towers with a two-hour fire rating. Grated steel stairs and landings are acceptable, but stair exits must have provisions to vent smoke, typically with a dedicated fan designed to produce a minimum pressure difference of 0.10 inch of water column and a maximum force of 30 pounds to open the doors, among other requirements.
Spaces not subject to human occupancy are exempt from egress capacity requirements. These spaces include scroll cases, generators, inspection access tunnels, draft tubes, and penstocks, according to NFPA 851.
Fire Doors. Fire doors leading to the stairwells must be kept closed at all times; using wedges or fusible links to hold the doors open is not permitted. However, the LSC permits the provision of automatic devices that allow the door to remain open but to close automatically in case of fire. If the entire powerhouse is provided with automatic smoke detection, then the electromagnets can be interlocked to automatically close the door(s) if smoke is detected in the powerhouse. As an alternative, consider using interlocking integral smoke detector/door closer assemblies. The LSC requires interlocking all automatic-closing doors in a stair enclosure so that the automatic actuation of one door closure device results in the closure of all automatic-closing doors.
Administrative Areas. Most powerhouses contain an administrative area that may be classified either as either an ancillary space or as business occupancy. As a rule of thumb, small offices used by operators or the shift supervisor, or as a break room, are considered to be ancillary and do not need to be classified as separate occupancy.
Conversely, a typical office setting with multiple offices, a reception area, and the presence of persons not intimately familiar with the hydroelectric facility (such as secretaries, accountants, and human resources staff) would qualify as separate business occupancy. In this case, the administrative portion of the powerhouse cannot exit into an industrial portion of the powerhouse. The office area must have its own exit arrangement, such as exit corridors and/or direct access to a stair tower.
Fire Alarms. The LSC requires the presence of a fire alarm system if the powerhouse occupancy is 100 or more persons and 25 or more of these occupants are above or below the level of exit discharge. In effect, just about all powerhouses will require a fire alarm system designed to meet NFPA 72. The proper design and installation of fire alarm systems is a separate topic that is outside the scope of this article.
Lighting. Emergency lighting in the event of power loss is required. The only exception is for powerhouses that are not "routinely inhabited," meaning unmanned powerhouses where operators only perform occasional checks and testing. Emergency lighting is not necessarily required throughout the powerhouse, but it is required in stairs, aisles, corridors, ramps, and passageways. Refer to NFPA 110, Standard for Emergency and Standby Power Systems, for specific requirements.
Some facilities require operators to carry a flashlight at all times. In one recent situation, a supervisor with a flashlight likely prevented multiple fatalities during a facility fire.
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