Basic Fire Protection Strategies
Put yourself in the role of the fire protection designer. The building plans sitting on your desk show one of several different building types: a large convention facility, a small office building, a chemical manufacturing plant, or maybe a high-piled storage warehouse. Your job is to decide the best approach to provide fire protection in this building. As you begin your task, one major question comes to mind: What steps can you take to evaluate the building for the fire protection needed?
Whether it is new or existing construction, an entire building, or only a portion of a building, both prescriptive and performance-based approaches can be taken to determine the fire protection required. You may be involved in designing a single fire protection system or in the entire design of the building, this article will give a brief overview of basic elements of fire protection and provide an outline of prescriptive and performance-based methodologies.
Passive fire protectionAll the elements for basic fire protection can be broken down into two categories: passive elements and active fire protection systems. Both rely on good design and installation techniques to provide the appropriate level of protection each system is expected to provide.
Passive fire protection measures are those that control the likelihood of ignition and fire growth and spread through material control or by providing physical barriers to the movement of flame or smoke. Passive fire protection systems are most often fixed in walls, floors, ceilings, beams, columns, and shaft enclosures that are built to a prescribed fire resistance rating. Fire alarm systems can be part of the passive fire protection used to initiate the closing of fire doors and dampers that may be otherwise held open to allow normal building function.
Passive fire protection systems are intended to maintain the following:
- Provide structural integrity of floor, wall, and ceiling assemblies during a fire for a specified time period.
- Compartmentalize the fire room or space to control the fire spread.
- Provide exiting systems for occupants to evacuate the building safely.
The goal of fire-resistive construction is to contain the fire in a small area and hold the fire in the room or area for the time given by the fire resistance specified in the construction. Fire-resistive construction provides protection to building occupants for the time period before building occupants are made aware of the fire, for the time period when occupants evacuate the building, and for firefighters performing an aggressive attack on extinguishing a fire.
Active fire protectionActive fire protection measures are those that take direct physical action to reduce the growth rate of fire or the migration of smoke. Active fire protection systems are most often fire sprinkler and smoke control systems that receive signals, both manual and automatic, to perform their intended function. Fire alarm systems are part of active fire protection used for activation of extinguishing systems or the notification of building occupants and the fire department.
Fire sprinkler and other extinguishing systems are intended to extinguish or control the fire. Smoke control systems are typically designed to limit the spread of smoke to perhaps maintain egress routes passable for a given period of time. The fire alarm, through both activation of the fire sprinkler system and manual or automatic detection devices, provides warning to the occupants of the building as well as notification to emergency personnel responding to the alarm.
Active vs. passiveNeither an active nor a passive fire protection systems are "better" than the other. Active fire protection systems should be provided in conjunction with the passive systems to provide a higher level of protection for both the structure and occupants than that provided by either of the general types of systems alone. An example of a joint use of systems would be a special "water wash" sprinkler design. This system would provide a fire-resistance rating on a glass wall assembly that exceeds the allowable design for fire-resistance rating that is necessary to the designer for function or visual effect. This is both an example of how active and passive systems can work together to provide adequate fire protection.
Installation and maintenanceFire protection systems are only as good as the design, installation, and maintenance of the systems. Passive systems do not have the same testing and inspection requirements or standards as active fire protection systems. Once the passive system is installed, inspected, and accepted by the building official and the certificate of occupancy is issued, the system is generally not re-inspected unless changes to the structure affecting the passive system occur. The only components of passive systems that may receive routine testing and inspection are the fire-rated doors or assemblies normally visible to the inspector. The parts of passive systems often overlooked for maintenance and testing are smoke and fire dampers. These devices require maintenance a minimum of every four years.
A passive fire-rated wall assembly can be voided with a simple hole that is cut through the wall by the TV cable installer. This hole may seem insignificant to the casual observer. Many unprotected openings in spaces above the ceilings, such as those for computer cables, additional duct penetrations, and electrical services routinely are added to the building after the certificate of occupancy has been issued and often are not repaired by the installer and are not inspected routinely.
Active fire protection systems, in addition to being inspected and tested upon installation, are required to be tested and maintained routinely after the building is occupied. The NFPA standards contain maintenance and testing schedules for various types of fire protection systems. The use of these schedules, or a modified version, is often mandated by the local authority having jurisdiction. It is important these systems be properly tested and maintained to ensure their proper operation, which is essential in providing effective fire protection in the building in which they are installed.
Prescriptive fire protection approachThe prescriptive fire protection approach entails the use of model building and fire codes to determine the appropriate fire protection for a given building or space.
Building codesThe new 2003 International Building Code (IBC); and each model building code, as published by Building Officials Code Administrators (BOCA), Southern Building Code Congress International (SBCCI), International Conference of Building Officials (ICBO), and the Life Safety Code and NFPA 5000 by the National Fire Protection Association, consider basic fire protection of structures in the fixed (passive) fire protection first. These codes then look to active (suppression or alarm) fire protection for the following reasons:
- The structure being considered exceeds a given size or height (depending on the occupancy type or piece of land where the building is to be located).
- The building has special features (for example, an atrium, covered mall, etc.).
- The occupancy is considered hazardous.
- The number of occupants is high.
The building codes prescribe fire resistance ratings for floor, wall, and ceiling assemblies. Shafts and special areas also are considered in the basic passive systems. Each model building code has tables and codes to provide guidance for fire ratings of the structures based on the size and occupancy of the building to be constructed.
The fire-resistance ratings of the floors, walls, and ceilings subsequently dictate the fire ratings of doors, windows, and fire/smoke dampers that penetrate the assemblies. The codes also specify the fire-resistance ratings for the structural columns and beams that will support the structure.
Active fire-protection systems come into play in the building codes when the building planned has exceeded the allowable area "footprint," allowable building height, or when special designs are planned. In addition, the building codes dictate active systems for specific occupancies. Active fire-protection systems (sprinklers) are allowed to replace passive fire-resistance ratings under special conditions. Special fire sprinkler designs are used in conjunction with passive systems to decrease the fire-resistive ratings as allowed by the building code.
Fire codes and design standardsThe designer should be aware that basic fire-protection designs also are found in each model fire code. When the design or use of the building is not specified in the building codes, the fire codes should be referenced for potential additional designs. Fire codes often dictate the basic fire-protection designs for many special-use areas. These areas would include flammable liquid storage and mixing rooms, high-piled storage areas, aerosol storage rooms, hazardous chemical use, storage areas, etc.
Both the building and fire codes refer to design standards for the design and installation of fire-protection systems such as sprinklers and fire alarms. Those fire-protection system design standards most often referred to are found in the NFPA National Fire Codes.
Performance fire-protection approachPassive and active fire-protection principles apply also when a performance-based approach is taken to the development of overall fire protection for a building. Rather than follow a rigid set of guidelines, this approach is based on evaluating the hazard presented and the development of the most appropriate method to protect this given hazard.
Different occupancies require different levels of fire protection. However, regardless of the type and proposed use of the building being evaluated, the same key considerations can be used to evaluate the amount and type of fire protection needed:
- Assess risks;
- Evaluate hazards;
- Manage fire impact; and
- Determine appropriate fire protection tools.
Assess risksThe amount and type of risk involved in certain occupancies, certain building contents, and who is in a position of accepting that risk can help determine the level of fire protection needed in a building or space. Ask yourself the following regarding the building you are reviewing:
- Do fires occur often in this type of building use? If fires occur often, an automatic suppression system may be the most appropriate protection.
- When a fire occurs, what are the most likely causes of the fire? Is a special fire-protection system needed at this source of ignition, or does this area need to be further separated from the rest of the building by fire-resistance-rated construction to contain the fire? The best example of this is special industrial occupancies.
- Is there a high risk to life safety when a fire event occurs? Can the occupants evacuate themselves, as at an arena or similar assembly building, or do the occupants depend on other people for evacuation, such as at a hospital?
- Does the building contain equipment that is highly susceptible to damage by smoke, water, or fire (e.g., a Web-hosting center)? If so, early detection of a fire and use of special extinguishing agents may be required.
- If a fire would result in significant downtime for the business, what are the implications? Do a large number of people go jobless, is business interrupted for an extended period of time?
- Does the loss of a product impact other operations? The reduction of business interruption depends on the quick activation of suppression systems, compartmentalization of the fire area, and rapid notification of the fire department.
The answers to these questions can help determine how much fire protection is needed in a building. For example, if there is a high risk to life safety in the building, the structure and exit paths should provide several hours of fire protection to facilitate evacuation and rescue. The building also should have a sprinkler system for additional protection of the occupants, and a complete smoke detection and fire alarm system for early occupant notification.
Evaluate hazardsIndividual hazards should be evaluated rather than the overall occupancy. The prescriptive building and fire codes lump similar occupancy types into a single method of fire protection. Using a performance-based approach identifies the hazards, needs, and key elements of the individual spaces to determine the appropriate fire protection. Consider the following:
- What size fires are anticipated? In some cases, with known combustible fire loads, fire dynamics can be used to evaluate the fire protection proposed. This can be effective in determining the time period necessary for fire-resistance rating of structural elements based on the size and length of the fire expected, as well as considering possible building fire-suppression system interventions.
- Is protection by only a sprinkler system acceptable?
- Is early warning needed for occupant evacuation or early suppression? The answers must consider the risk assessment and the acceptable amount of exposure to building occupants and fire damage.
- Will sprinklers be effective on the type of fire anticipated or is a special extinguishing agent needed for fire suppression?
- Is it necessary for emergency power to be turned off before firefighting operations are conducted?
Manage fire impactThe intent of specified fire protection systems is to manage the fire and limit (to an acceptable level) the exposed elements. The key is to set goals for the fire protection system, such as minimizing business downtime after an incident or protecting occupants not in the room of the fire's origin. Determine what amount of damage is acceptable if a fire occurs.
Fire protection toolsBoth passive and active fire protection systems are acceptable fire protection tools to be used in building and occupancy protection. The fire protection chosen depends on the answers to questions such as those above. Properly coordinated fire-protection systems to match the key considerations are the foundation of a well-designed building for fire protection and life safety purposes.
If early occupant notification is needed for immediate evacuation or early fire department notification is needed to conduct adequate fire fighting operations, a partial or complete smoke detection and fire alarm system is appropriate with automatic notification of the fire department. If fire damage is to be minimized, it is important that adequate compartmentalization is provided in the building to reduce fire and smoke spread and extinguishing systems are provided to limit the size of the fire.
SummaryProperly coordinated, designed, installed, and maintained fire- protection systems have and will continue to protect property and save lives. Passive and active fire protection systems working together complement one another and protect against "flaws" in a single system design during the life of the building they protect. The approach to determine the appropriate fire protection systems in a building can be either prescriptive (using building and fire codes) or performance-based (evaluating the specific hazards of a use and determining the appropriate fire protection), or both. ES
Rolf Jensen & Associates, Inc. is a national engineering consulting firm providing fire protection and code consulting services. To learn more about RJA visit their website at www.rjagroup.com.