Reducing the Risk of Fire on Your Farm - Preventing Fire Spread
Table of Contents
Design Codes and/or standards are minimum requirements established to protect the lives of people and the contents in farm buildings. Codes describe correct farm building materials to use to reduce the number of ignition sources, reduce the rate fire spreads within buildings and establish separation distances for fire spread to other buildings. These Codes are in place because barn layout and construction materials greatly influence the fire risk associated with a given site.
When discussing fire safety, prevention, precautions and procedures are often included. Prevention, as highlighted in this section, deals with ways to prevent the initial source of ignition from spreading and prevent fire from starting in adjacent areas.
One of the key concepts of fire safety in all buildings, including farm buildings, is to limit the spread of fire throughout a building with a physical barrier, known as a fire separation. A fire separation can be a wall, ceiling or floor of a building (Figure 3.1). Several fire separations are often used in combination to surround a given space and contain fire within it; this space is termed a fire compartment.
Figure 3.1. Example of a fire separation that served its purpose in a swine complex, preventing the fire from spreading to the rest of the barn. (Photo credit: R. Drysdale, Farm Mutual Reinsurance Plan)
A wall, when put together or constructed in a building, is known as a wall assembly. Similarly, ceilings and floors, once built, are referred to as ceiling and floor assemblies.
Wall, floor and ceiling assemblies of buildings are built in different ways using a variety of construction materials. The way these assemblies are constructed determines how long it will take a fire to burn through the assembly and penetrate from one fire compartment to another. Wall, floor and ceiling assemblies built as required fire separations are usually given a specific fire-resistance rating to meet.
A fire-resistance rating is a measure of the length of time a properly constructed and maintained assembly can withstand fire conditions. In the case of a fire separation, a fire-resistance rating identifies the time for a fire to burn through from one compartment to another (30 minutes, 1 hour, 2 hours, etc.).
Examples of common wall assemblies used as fire separations in farm buildings are shown in Table 3.1. It is important to note that the fire-resistance rating of a construction assembly is for a specific configuration of structural elements. A similar wall component may behave differently if it is located in a ceiling.
1Additional information on fire-resistance ratings for assemblies is given in Ontario's Building Code.
2Interior walls are rated from both sides, whereas floors and roofs are rated from below.
3Use gypsum wallboard in farm buildings only in specific locations.
Source: National Farm Building Code of Canada, 1995
*2006 Building Code Supplementary Standards SB-3, page 2
Fire separations must be continuous. Except for openings in the outside face of a building, provide openings in fire separations around a fire compartment with properly rated closures. Use appropriate construction materials to ensure all gaps are fire stopped. In a number of situations where it is not practical to avoid openings, special measures are taken to limit the spread of fire through these openings. See the section on Protection or Closure of Openings in Fire Separations.
Figure 3.2. Example of a common one hour fire separation. Where drywall is used in high moisture areas, provide a vapour barrier in an appropriate location that protects the drywall.
Containing the electrical/mechanical room in farm buildings is an example of a fire separation that provides a valuable compartment to prevent the spread of fire. Equipment such as standby generators or compressors for refrigeration units can overheat and start a fire. Having a continuous fire separation around this equipment often provides enough time to extinguish the fire before it spreads to the rest of the building causing a total loss of the structure.
With the exception of specific heating and cooling equipment, the NFBCC further requires a fire separation with a minimum rating of 30 minutes between fuel-fired appliances, crop drying and equipment repair rooms, and the remainder of the building. The Technical Advisory Committee on Farm Fires (TACFF) recommends increasing these fire separations to one hour for buildings containing liquid fuel storage or highly combustible materials such as hay or straw.
To reduce fire losses and as a best management practice, TACFF recommends paying increased attention to the construction and maintenance of fire separations.
A fire compartment is a usable, enclosed space in a building that is separated from all other parts of the building. Many Codes specify maximum compartment sizes, to contain a specific fire risk within an area and protect people in the rest of the building. For the concept to work, compartment boundaries must have an adequate level of fire-resistance. All openings and penetrations through these boundaries require protection with rated closures or fire stops. The level of fire-resistance required depends on many things including the building size and type of occupancy.
The NFBCC does not limit the building size of farm buildings, but specifies that where the floor area exceeds the maximum size (Table 3.2), the building be separated into fire compartments.
Source: National Farm Building Code of Canada, 1995.
Review existing farm buildings to assess the practicality of reducing fire compartment sizes to conform with building area limits established in Table 3.2.
Consider these sizes when designing new buildings. For a one storey barn, the NFBCC allows a maximum compartment size of 4,800 m2 (51,600 ft2). If the building footprint is larger than 4,800 m2, the designer's challenge is to maximize the overall efficiency of the layout and achieve all the safety objectives for compartmentalization.
For example, dividing a large free stall dairy barn, 33 m (110 ft) wide x 198 m (650 ft) long, into two compartments to meet the compartment size requirement would involve erecting a fire separation wall near the midpoint of the 198 m (650 ft) length. Since the cow alleyways and the central feed alleyway run on the long axis of the building, this would result in five large door openings in the fire separation equipped with closure devices (fire doors). This layout could negatively impact equipment and cow traffic, and air movement in the barn (Figure 3.3).
Figure 3.3. A large free stall dairy barn with fire separation wall at the midpoint.
From a fire separation stand point, it is more effective to erect several free stall barns that each measure less than 4,800 m2 (51,600 ft2). These barns could be spaced at least 30 m (100 ft) apart and interconnected with hallways to house the animals. One closure device (fire door) located in the middle of each connecting hallway enables the design to meet the fire compartment size requirements, and minimize flow issues associated with cow and equipment traffic, and air movement (Figure 3.4).
Figure 3.4. The fire compartments formed by several fire separations will slow the spread of fire and provide a better opportunity to fight a fire in this large building complex.
To reduce fire losses, and as a best management practice, TACFF recommends using smaller compartment sizes in farm buildings with properly constructed fire walls and separation distances.
Fire stopping is another key concept for fire safety in all buildings, including farm buildings. Fire stops are used to limit the spread of fire throughout a building with a physical barrier in concealed spaces.
Fire stops are usually located within walls, floors, ceilings and in attic spaces. Fire stops are commonly constructed with solid lumber not less than 38 mm thick (1 ½ in.). Fire stops in concealed spaces should conform to the provisions in the NFBCC. As noted in the Ontario Construction Guide for Farm Buildings 2003, fire stops in farm buildings reduce the spread of smoke and flames within concealed spaces, giving people time to escape in the event of fire. Properly installed fire stops also prevent rodents and birds from easy access throughout the same concealed spaces, making the buildings more durable while increasing fire safety. Figure 3.5 shows a typical two storey barn cross-section.
Figure 3.5. A two storey barn cross-section showing fire stopping locations.
Attic fire stops limit fire from moving quickly through the attic space of a building. The NFBCC requires fire stops in attic spaces be constructed at intervals no greater than 30 m (100 ft) in either direction. Construct fire stops to ensure there are no openings to allow fire to move quickly to the next space. Fire stops are commonly constructed using the following sheathing materials:
The sheathing materials are often mounted on one side of the roof trusses in the attic space (Figure 3.6). The truss manufacturer can provide specific guidance if required. In all cases, the joints must be backed with similar material and sealed to create a draft-tight barrier to restrict the passage of smoke and flame.
Figure 3.6. Example of an attic fire stop under construction in a new calf barn.
Attic fire stops are one of the most neglected construction details in farm buildings. Pay particular attention to the tightness of the construction since it provides the critical function of reducing the rate of fire spread. If the fire stop is pierced with wiring, plumbing or ductwork, the space between the stopping material and the object piercing must be sealed and caulked with fire-rated material. A fire stop is expected to slow the progress of a fire by at least 15 minutes.
Unfortunately, the lack of proper attic fire stops, or breached fire stops in the attic, has contributed to the rapid progression of fires in several Ontario swine barns. Figure 3.7 shows a fire stop that has been breached by an opening, and would allow a fire to jump into the next attic compartment without slowing down.
Figure 3.7. This attic fire stop has an opening cut into it (arrow), removing its effectiveness in containing a fire. (Photo credit: Randy Drysdale, Farm Mutual Reinsurance Plan)
Protection or closure of openings in fire separations
Ontario's Building Code and the NFBCC requires any permanent opening through a fire separation, like a doorway, window, etc., be equipped with a closure device. Closure means a device or assembly for closing an opening a door, shutter, wired glass or glass block and includes all components, such as hardware, closing devices, frames and anchors.
These closure devices close automatically during a fire to seal the opening (e.g. a metal roll-up door with a fusible link). Figure 3.8 shows a roll-up fire door controlled by a fusible link. When a higher temperature is encountered, as in a fire, the fusible link melts and the door closes to protect the adjoining compartment. Inspect all fusible links annually to identify signs of premature deterioration. Ensure this inspection is completed by a qualified individual.
Figure 3.8. This roll-up door protects an adjoining compartment by automatically closing in a fire. (Photo credit: Cornell Iron Works Inc., Pennsylvania)
Ventilation openings in naturally ventilated farm buildings present a challenge for designers looking to maximize a building's fire safety characteristics. These buildings have large openings in the sidewalls to allow the required air flow into the barn, providing a comfortable environment for livestock during warm weather conditions. During a fire, these large openings perform the same function, allowing large volumes of air to enter the building and provide oxygen to feed the fire. These unrestricted wall openings also present challenges where two buildings meet, providing a location for a fire to "jump" from one building to the other.
Proper location of fire separations in these buildings is critical to prevent fire spread. Construct the wall immediately adjacent to the fire separation as a solid wall without ventilation openings, to help stop a fire from jumping the fire separation. Another way to avoid this problem is to locate fire separations in hallways between buildings at a sufficient distance from other openings (Figures 3.9 and 3.10).
Figure 3.9. Unacceptable location of fire separation doors. This door location is unacceptable since a fire can easily jump past it.
Figure 3.10. Acceptable location of fire separation doors. This door location is acceptable since a fire cannot easily jump past it.
To reduce fire losses, and as a best management practice, TACFF recommends increased attention to fire stopping.
Fire spreads by convection, conduction, radiation and/or direct flame contact. Spatial separation is a concept that reduces the chance of a fire spreading by radiation to adjacent buildings.
Radiation is the transfer of heat from flames and hot surfaces to solid objects that are in the direct path of the heat source. The hotter the source and the greater its ability to emit heat, the better the radiant heat transfer to objects in its path. On a smaller scale, radiation in everyday life is one way gas fireplaces transfer heat throughout houses.
Fire spreads by radiation to neighbouring buildings when nearby materials absorb enough heat and begin to smolder and then burn. Providing enough distance between all buildings helps minimize heat gain between the source of the fire and the surfaces of adjacent buildings. This distance gives firefighters the opportunity to apply water to the nearby building surfaces in an effort to reduce the temperature of each surface.
It is more efficient and practical to incorporate the recommended spatial separations for farm buildings at the design and siting stage, before construction begins (Table 3.3).
As a best management practice, TACFF recommends that new buildings are set back from lot lines a minimum of 30 m (100 ft) to protect buildings on neighboring properties.
It is important to understand how fire spreads. Compartments contain fire within a certain area, but designers also strive to reduce the rate at which flames and smoke spread within each compartment. Slowing down the development of a fire within a compartment provides more time for people to escape, and increases the chance that the fire is manageable when the fire department arrives. Selection of interior sheathing materials significantly impact the rate fire spreads within each compartment.
The availability of new materials for barn construction provides designers, builders and operators with more cladding options than ever before. Choose interior finish materials with low flame spread ratings that do not support combustion, for example, concrete or tile surfaces and to a lesser extent steel sheathing. When steel is subjected to high heat, it buckles and air gaps may open at the sheet overlap joints, allowing the fire to penetrate into the wall or ceiling cavity. Noxious gases and smoke are given off by most building materials in varying quantities. While many plastic and vinyl materials show low flame/spread ratings, they melt very quickly when ignited. If used on the walls and ceiling without any backing materials like drywall, the melted product leaves openings where fire can spread quickly into wall and attic spaces (Figure 3.11).
Figure 3.11. Melted vinyl sheathing on ceiling. Note the lack of backing behind the vinyl leaving the attic space exposed. (Photo credit: R. Drysdale, Farm Mutual Reinsurance Plan)
Specific sheathing materials contribute to the spread of flames at varying rates. Materials give off varying amounts of smoke as they burn. Table 3.4 provides a guide to the characteristics of some common interior sheathing materials.
1FSR values relate to a classification system for various substrates that indicate how far flames will spread in a given amount of time.
2SDC values are related to the smoke concentrations given off from burning materials.
Note: The NFBCC requires that foamed plastic insulation materials are protected or covered. There must be no foamed plastic exposed to the spaces occupied by people and livestock as many foamed plastic insulations can be accidentally ignited by sparks and other ignition sources. Once these foams are ignited, people and livestock are at risk because the foams quickly produce flames and toxic smoke. Two suitable covering materials are exterior-grade plywood and galvanized sheet steel since they have acceptable levels of fire protection, durability and moisture resistance.
Plastics create very noxious gases when burned. At very high temperatures, the gases that develop may suddenly cause flashover of the entire room and increase the rate of fire spread.
Installation of drywall in a high moisture area, like a livestock barn, is not recommended due to the high humidity levels in the housing area. Where drywall is used, provide a vapour barrier in an appropriate location that protects the drywall from the high moisture environment.
Drywall can be used in dry environment areas of the barn that do not house livestock. For example, use two layers of fire-rated drywall to line the interior of the mechanical electrical room to provide a fire separation. A fire that starts in this area will take longer to spread to the rest of the building, providing more time for evacuation and extinguishing.
For harsh environments (humid and corrosive), choose durable sheathing materials that often have a higher fire-resistance rating (i.e. concrete board, sandwich wall construction, fiberglass-coated plywood).
There are nine key recommendations to reduce the effects of the corrosive atmosphere in the livestock or poultry housing area of the building.
Figure 3.12. Wet-rated cord caps. Cap is a term the electrical industry uses to describe either male or female cord ends or plugs. (Photo credit: Electrical Safety Authority)
Figure 3.13. The heat lamp is connected directly to a wet-rated electrical box and includes a wet-rated cord cap connection so the lamp fixture can be removed. When the lamp is removed, the cover is placed on the female cap end to protect it from corrosion.
The TSSA Fuels Safety Program administers the fuel-related safety services associated with the safe transportation, storage, handling and use of hydrocarbon fuels (i.e. gasoline, diesel, propane and natural gas in Ontario).
Figure 3.14. A box heater properly suspended on four jack chains. Note that a faulty gas valve resulted in charring of the electrical conduit. (Photo credit: R. Drysdale, Farm Mutual Reinsurance Plan)
As a best management practice, TACFF recommends constructing a one hour fire separation wall between the dedicated room housing the fuel-fired appliance from the rest of the building.
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