Contributed by William Eppich
Such a terrible, unforgettable sight – in the blink of an eye, fire can destroy a barn structure and all its occupants while humans stand back and watch helplessly. It follows that the largest fire and most spectacular incident that many small community and rural fire departments face is the common barn fire. Yet, in the mindset of owners of these structures they cannot believe it would happen to them, so any means of fire detection/prevention is often overlooked, and they leave fire protection entirely to chance. However, the fact remains that annually more than 1,200 barn fires, most of them preventable, occur each year in the United States and result in nearly $33 million dollars in property damage. To date, only a few states have mandated fire codes for their agricultural community and barn structures, and the science of fire protection still remains as a necessary evil for too many owners of barns who think “it can’t happen to me.”
Protecting a barn is more difficult than common residential structures in view of the large open areas without sectioned areas to confine a fire, construction mostly of combustible building materials, large open doors and loft windows to accelerate air flow along with a heavy fuel load, and the harsh barn environment and housing requirements for hay, feed, and maintenance equipment. However, the main cause of 90% of un-intentional barn fires result from carelessness with smoking, electrical equipment malfunctions, arson and natural causes from lightning. Because barns typically consist of large floor areas occupied by only a few personnel, a fire may go undetected for a long period of time after it starts. In most cases, when flames are seen, it is probably too late since the damage caused by fire grows exponentially with the amount of time it has burned. It would seem logical that most barn fires occur in the winter at a time when forage and bedding storage is greatest, electrical usage is high, and equipment repairs and upgrades are typically high. Preparation and planning, therefore, is the greatest asset in fire prevention.
In terms of fire detection for barn applications, many types of residential or commercial devices are available that would seem to be applicable to a barn installation, however, residential design criteria do not take into account the harsch, somewhat aggressive environment found in a typical barn, such as dust, dirt, chemical presence from droppings and urine, vibrations from electrical equipment and animal movement, and seasonal temperature variations. These applications would be best served by devices specifically designed for industrial applications and more suited to the barn environment. An overview of fire detection devices normally used for similar industrial applications would require a brief overview of the more typical devices that may be applied to a barn fire detection system.
Fire Detection Devices and Principles
Smoke consists of particulates as well as gasses. The particulate matter is mostly carbon based by-products of combustion and bits of unburned material. Smoke will seep out of small gaps even if the fire is mostly confined. Several technologies are available for sensing smoke, including detectors based on ionization and electrostatic phenomena as well as photoelectric opacity sensing and emissivity techniques. New technology in aspirated smoke detection technology has emerged which can measure finite particles of smoke emission by continuously sampling the surrounding air with laser smoke chambers and result in greater sensitivity to smoke particles than conventional ionization and photoelectric smoke detection devices. In practice, however, all of these devices for sensing smoke can be vulnerable to false alarms from fumes, dirt, dust, moisture, and sometimes electrical interference. While smoke will develop previous to a fire, one would hope to detect the combustion cycle at the ignition stage during a slow development of heat, eventually to developing smoke, since heat must be developed before smoke can develop. Logically, then, smoke detection would be applicable to non-aggressive areas of the barn in offices, equipment room, tack rooms, or other areas where fast raising combustion may occur from burning paper or cartons.
Radiation (Flame) Detection
The characteristic of radiation from a flame can be sensed before significant heat is released. The specific wavelengths of radiation released depend on the specific substance undergoing oxidation, though the fire spectrum will generally be in the same band. Radiation of a fire occurs in the infrared (IR) bands and ultraviolet (UV) bands. The primary sensing technology of interest is those measuring UV and IR radiation. Since any type of fire will develop radiation depending on the ignition source of the flame, this type of detection technology is the fastest available, with detection times instantaneously in milliseconds once the detector “sees the fire.” Once again, however, detection before ignition is a primary consideration to consider when designing a fire detection system. The drawback when considering flame detection in a barn environment is the maintenance required to assure that the detector lens is clear of dust, dirt and other airborne particles, including moisture, that dry on the quartz lens of the detector. The cost of flame detectors unquestionably places them quite above conventional detection means despite their superior detection to a flame.
Heat detectors are generally used where other types of detectors would be unsuitable in aggressive or harsh environments. While heat detectors may appear to be slower to detect the by-products of fire, they still remain the most reliable detection devices available in view of their reliabilty, robust construction, low maintenance and proven response times. Heat detectors are available with a variety of operating principles as either area type (rate compensated, rate-of-rise, spot) or linear type (thermo resistive, fiber optic). Unlike conventional heat detectors, which are typically placed on ceilings far above sources of ignition, linear heat detectors are typically used as proximity detectors, that is, they are placed in direct contact to the suspected source of overheat on motor and generator casings, cable trays, electrical lines, and in hay piles where sources of ignition from spontaneous combustion occur. The advantage of a linear heat detector for specific applications is their response to overheat development long before smoke and ignition development. Linear heat detectors are capable of monitoring long lengths, typically 5,000 feet continuously where every infinite point along the length is an alarm point, thus they may be placed in concealed areas or locations where other types of detectors would be unsuitable, such as around the perimeter of stalls at the floor level, and inside electrical panels. Compared to a conventional heat detector whose sensitivity is maximum in the vicinity of the detector, linear heat detectors have no loss in sensitivity since the alarm points are infinite continuously. The advantage of a linear heat detector for specific applications is their response to overheat development long before smoke and ignition development. The low cost and high reliability make this type of aggressive detection the choice of engineers and designers based on its use in similar applications for over 70 years.
Sprinkler systems are an effective device for controlling fires but are seldom found in barns. One reason for the scarcity is the installation expense. Retrofitting a barn or stable with a sprinkler system costs perhaps as $2.00 per square foot depending on the structural circumstances and available water supply. However, a sprinkler system can suppress a fire with the activation of a few sprinkler heads and is effective at controlling fires before they spread and get out of hand. Yet, in order to be effective, an adequate supply of water must be available at all times through seasons of a year. Unfortunately, it is difficult for many rural barns to meet these criteria. Typically, one sprinkler head will require 25 gallons of water per minute to extinguish a fire. As more sprinklers are activated, more water must be available to maintain proper pressure in the line. If primary water supply is a problem, an underground or standby water tank may be utilized for the supply.
Geographical location of the facility will determine the type of sprinkler system used. In warm climates a wet system is installed which has water in the sprinkler pipes at all times available for immediate release upon sprinkler head activation. In colder climates, where the danger of sub-zero temperatures will exist, a dry pipe or pre-action sprinkler system is required to prevent accidental valve release and water flow. These systems continually have an air pressure supplied by a pump in the sprinkler piping to keep the piping dry during low ambient temperatures. Upon an overheat or alarm detected by a control panel and detection device, the sprinkler operating valve will open and allow water to flow once the air pressure is exhausted from the piping from a sprinkler head opening due to the fixed temperature setting of the sprinkler head. Pre-action and double interlocked pre-action systems are typically used for cold storage and refrigeration facilities where sub-zero temperature is the normal ambient temperature and their use is well proven at these ambient temperatures. Unquestionably, the safest barns would be protected by an automatic sprinkler system and associated detection devices monitored by a control panel. Unfortunately, until barns become mandated to include an automatic fire detection system, the risk of total destruction will remain. For detailed design information on protecting barns and animal housing facitlities, the National Fire Protection Association has established NFPA 150 Standart on Fire and Life Safety in Animal Housing Facilities as a guide for protecting these valuable structures.
An example of the intuitiveness of a large horse barn owner may be illustrated by a complete automatic fire detection system recently installed in a horse barn at the Stillwater Farm located in Pembroke, Massachusetts. The owner, Andrew Sullivan, considered the importance of installing the appropriate detection devices in various sections of the barn which required each type of detector to serve the appropriate hazard. After an evaluation of the potential combustible materials and storage areas, the following areas included the following technologies:
- Linear heat detection is installed in all concealed areas including electrical raceways, overhead beams, stall areas, hay storage and electrical panels
- Conventional heat detectors installed in wash rooms, fee preparation area, and tack rooms
- Aspirated smoke detection (air sampling) installed in second story personnel area, main walkway in main barn
- Flame detection (radiation) installed in hay storage areas
- Manual pull stations installed at entry/exit doors
- Automatic sprinkler system installed throughout main barn area, equipment rooms, and hay storage
- Horn/strobes installed externally
All detection devices terminate in a master control panel for monitoring multiple zone areas and connected to a digital phone dialer for annunciating to the local fire service.
Recognizing that fire prevention will never be 100 percent successful, it is necessary to plan and design so as to reduce property loss when fire occurs. The various strategies to accomplish this constitute what is usually referred to as fire protection. It is important to understand that fire protection requires the development of an integrated system of balanced protection which uses many different design features and systems to reinforce one another in case of failure of any one. This means that success is measured by the extent of usage of effectively designed, integrated fire protection systems. It’s obvious, then, that an integrated barn fire protection system as the one described above, represents a fractional investment to protect the property and animals of an owner.
William Eppich is the Vice President of International Sales at Protectowire, Inc. He has more than 30 years’ experience in the fire protection industry and is a member of the NFPA Technical Committee for NFPA 520 Standard on Subterranean Spaces.