Frequently Asked Questions

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2018-08-13T18:53:36+00:00

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Questions about fire protection? In this section you will find additional information about the services we provide. Knowledge is power, and in fire protection, knowledge saves lives.

Please feel free to contact us should you have any additional questions, we are here to help!

Portable Fire Extinguishers

Kitchen Fire Supression & Hood Cleaning?

Automatic Sprinkler System

Backflow Devices

Fire Alarm Systems

What are Fire Classifications?

There are five different classifications of fires. You must properly match the class of extinguisher with the potential hazard:

Class A Fires

These fires are considered ordinary or common combustibles including wood, paper, cloth, rubber, household rubbish, and some plastics. (Label is normally Green in color)

Class B Fires

These fires involve flammable liquids including oils, grease, tar, lacquers, flammable gases, oil-based paints, and some plastics.  (Label is normally Red in color)

Class C Fires

These fires involve energized electrical equipment including computers, building wiring, circuit breakers, light fixtures, and appliances.  (Label is normally Blue in color)

Class D Fires

These fires involve combustible metals including magnesium, titanium, zirconium, sodium, lithium, and potassium.  (Label is normally Yellow in color)

Class K Fires

These fires involve combustible cooking media including vegetable or animal fats and oils.  (Label is normally Black in color)

What are the Extinguisher Sizes?

In the past, the sizes of fire extinguishers were determined by the amount of chemical inside of the extinguisher. Independent testing labs (Underwriters Laboratories and FM Approvals) test extinguishers to the UL/ANSI 711 Rating and Fire Testing of Fire Extinguishers for their ability to extinguish specific classes and sizes of fires. In 2002, attempts to standardize the various test protocol differences between UL and ULC were initiated. As of August 14, 2007, all fire equipment manufacturers are required to comply with the new testing standards.

Class A Extinguishers are labeled with a number from 1 to 40.The number is an expression of the extinguisher’s fire-fighting effectiveness. The larger the number, the larger the fire the extinguisher can be expected to extinguish.

Class B Extinguishers are labeled with a number from 1 to 640.The number is an expression of the extinguishers fire-fighting effectiveness. The larger the number, the larger the fire the extinguisher can be expected to extinguish.

There is no numeric designation for an extinguisher’s effectiveness in fighting Class C, D, or K fires. The letters C, D, or K tell you only that the unit has been rated to combat energized electrical equipment, combustible metals, or cooking oil fires.

What is the Area Hazard Classification?

The class and the size of fire likely to occur in a particular area are key factors in determining the appropriate type and size of extinguisher to be used. Together, the class and size of a potential fire define the hazard for which your extinguisher installations must be designed.

Hazard Classification: (per the National Fire Protection Association Standard for Portable Fire Extinguishers):

Light (Low) Hazard

Light (Low) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustibles and Class B flammables are low and fires with relatively low rates of heat release are expected

Ordinary (Moderate) Hazard

Ordinary (Moderate) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustible materials and Class B flammables is moderate and fires with moderate rates of heat release are expected.

Extra (High) Hazard

Extra (High) hazard occupancies shall be classified as locations where the quantity and combustibility of Class A combustible material is high or where high amounts of Class B flammables are present and rapidly developing fires with high rates of heat release are expected

It is important to properly determine the hazard level for all areas. You may be required to install multiple extinguishers or extinguishers with multiple ratings. Restaurants for example, require multiple extinguishers due to multiple hazards. Low hazards in dining areas would require a Class A extinguisher, and high hazards in the kitchen would require a Class K extinguisher.

Special considerations have to be made with Class B fires. There are four typical types of flammable liquid fires:

  • Fire involving liquids at least 1/4″ deep.
  • Spill fires in which the burning liquid is less than 1/4″ deep.
  • Fires in which the burning liquid or gas is under pressure.
  • Three dimensional fires, involving burning liquids that are in motion.

Deep liquid fires build up more heat than spill fires and are best extinguished with agents that smother the fire such as foam. Spill fires can be brought under control with carbon dioxide or dry chemical extinguishers. Gas under pressure can only be controlled with dry chemical. Extinguishers used for fighting pressurized Class B fires must be outfitted with a special nozzle, which allows for the rapid release of more dry chemical. These extinguishers are known as fast flow extinguishers.

How Many Extinguishers are Required?

There are four topics to review when installing portable fire extinguishers. You must first identify the hazards that are present, and recognize even trace amounts of each fire classification to determine the proper number of extinguishers required. Next, you must determine the size of the fire extinguisher, and establish the quantity of extinguishers needed by the coverage allowed per Local and National fire codes. Last, you must distribute the portable fire extinguishers per the allowable travel distance to each fire extinguisher.

Class A Locations

Criteria

Light (Low) Hazard Occupancy

Ordinary (Moderate) Hazard Occupancy 

Extra (High) Hazard Occupancy

Minimum Rated single extinguisher  2-A 2-A 4-A
Maximum floor area per unit of A  3,000 ft2 1,500 ft2 1,000 ft2
Maximum floor area for extinguisher  11,250 ft2 11,250 ft2 11,250 ft2
Maximum travel distance to extinguisher 75 ft 75 ft 75 ft

 Source: NFPA 10, 2007 edition Table 6.2.1.1 Fire Extinguisher Size and Placement for Class A Hazards

Class B Locations

Type of Hazard 

Basic Minimum Extinguisher Rating 

Maximum Travel Distance to Extinguisher 

  5-B 30 ft
Light (Low)  10-B 50 ft
  10-B 30 ft
Ordinary (Moderate)  20-B 50 ft
  40-B 30 ft
Extra (High)  80-B 50 ft

Source: NFPA 10, 2007 edition Table 6.3.1.1 Fire Extinguisher Size and Placement for Class B Hazards

Class C Locations

Class C extinguishers are required where energized electrical equipment is directly involved in or surrounding electrical equipment.

Class D Locations

Class D extinguisher locations shall not be located more than 75 ft. from the hazard. Size determination for Class D locations is based on the specific combustible metal, particle size, area to be covered, and manufacturer recommendations.

Class K Locations

Class K hazards shall have a fire extinguisher located where there is a potential for a fire involving combustible cooking media (vegetable or animal oils and fats). The extinguisher shall be located no more than 30 ft. from the hazard.

NFPA 10 requires you to maintain your fire protection equipment in good working order and maintain inspection,
testing and maintenance records. Inspections will be performed on an Annual basis.

Examples of Work Performed During An Inspection Include:

  • Check that unit is properly hung with the proper manufacturer’s hanger.
  • Check the gauge pressure.
  • Check the condition of the gauge and its compatibility with the extinguisher.
  • Check the weight of the extinguisher.
  • Check that the last hydrostatic test date is within code requirements.
  • Check the last 6−year maintenance inspection date if applicable.
  • Check the valve and shell for damage or corrosion.
  • Remove the hose and inspect it for cracks or splits.
  • Check the hose threads for signs of wear.
  • Check the condition of the discharge horn.
  • Check for obstructions that interfere with accessibility of the unit.
  • Break the extinguisher seal and remove the locking pin.
  • Replace the locking pin and reseal the extinguisher.
  • Check the valve opening for powder or any foreign matter.
  • For dry extinguishers, fluff the powder by turning the unit.
  • Check the condition of the hose/horn retention band at the side of the extinguisher.
  • Check that the unit’s classification is properly identified with the appropriate decal/signage.
  • Check that the operating instructions are clean and legible.
  • Check that the unit is properly located within the normal path of travel, at the required height.
  • Check that the unit is visible, unobstructed and in proper location.
  • Compile a complete location report, explaining any deficiencies.
  • Recommend corrective action to be taken in accordance with recognized codes for care and maintenance.
  • Upon completion of inspection and any necessary repairs, applicable inspection documents and noted deficiencies shall be left at location and available electronically.
  • Tag all portable fire extinguishers as required and perform required record keeping.

 Extinguisher Type

Test Interval (years) 

Stored-pressure water, water mist, loaded stream, and/or anti-freeze 
Pump tank water and pump tank calcium chloride base 
Dry chemical, cartridge and cylinder operated, with mild steel shells 
Dry powder, cartridge and cylinder operated, with mild steel shells 
Wetting agent 
Stored pressure water   5
Stored-pressure dry chemical, with stainless steel shells   
Carbon dioxide 
Wet chemical 
Dry chemical stored-pressure, with mild steel shells, brazed brass shells, and aluminum shells 
Halogenated agents 
Dry powder, stored pressure, with mild steel shells 

What is the difference between a wet and dry chemical system?

Wet Chemical Systems

A wet chemical system is the most commonly used fire suppression system to extinguish cooking oil fires.  It is the primary source of extinguishing kitchen fires. The wet chemicals suppress fire by a process called saponification. Saponification is a chemical reaction that occurs when a vegetable foil or animal fat is mixed with a strong alkali.  Saponification value is a measure of the amount of potassium hydroxide needed to neutralize one gram of fat or oil.  The most common types of cooking media, i.e., animal fats (or lard), vegetable oils, and peanut oils, have similar saponification values.  Other fats, such as cocoa, have substantially higher saponification values and therefore are more difficult to extinguish

Dry Chemical Systems

A dry chemical system is primarily used to extinguish flammable liquid fires that are not of appreciable depth.  Because it is non-conductive, it can also be used on flammable liquid fires involving live electrical equipment. Dry chemical interrupts the chemical reaction of fire by removing the oxygen from the source.  When the multipurpose dry chemical is discharged into burning ordinary combustible, the decomposed monammonium phosphate leaves a sticky residue (metaphosphoric acid) on the burning material.  This residue seals glowing material from the oxygen, thus helping extinguish the fire and prevent re-ignition.

What is the difference between a wet and dry sprinkler system?

Wet Sprinkler System

Wet sprinkler systems are the most common type of sprinkler system installed. A wet pipe system has water in the pipes in the ambient or normal condition and has heat responsive elements on all sprinklers. Thus, water is instantaneously discharged from a sprinkler when it actuates.

Dry Sprinkler System

A dry sprinkler system is intended to be used In areas where low temperatures could cause a wet pipe system to freeze.  Dry pipe systems are pressurized with air in the ambient condition and experience an inherent delay in the discharge of water to allow the pressurized air in the system to escape.  When a sprinkler actuates, air is released through the sprinkler, allowing water to flow into the piping system through the dry pipe valve. NFPA 13 mandates that the time for the water to reach the most remote sprinkler be no longer than 60 seconds.  This time delay allows the fire to grow larger than it would with a wet pipe system of similar design, and the larger fire size results in more sprinklers in the fire area actuating.

What are pre-action and deluge sprinkler systems?

Pre-action and deluge systems require fire detectors (smoke, heat, etc.) to actuate.

A deluge system uses open sprinklers or nozzles to allow flow water to be discharged when the deluge valve actuates. Deluge systems can be used for occupancies where the hazard is considered severe, such as with flammable liquid hazards where the fire could spread over a large floor area.

Pre-action systems have closed heads and pipes filled with pressurized air that supervise a piping system, and can be considered for the protection of valuable assets or irreplaceable property. The detection system for a pre-action system can be designed to prevent water discharge in cases of a false alarm from the detection system, or in case of a sprinkler whose element has encountered mechanical damage.

The detection system on a pre-action system can be designed with a pre-action logic capable of meeting one of the following objectives:

  • Actuation of a fire detector trips a deluge valve to admit water into the sprinkler piping to await the actuation of a sprinkler.
  • Actuation of a fire detector or actuation of a heat-responsive element on a sprinkler trips a deluge valve to allow water into the sprinkler piping.
  • Actuation of a fire detector and actuation of a heat-responsive element on a sprinkler trips a deluge valve to allow water into the sprinkler piping

Automatic Sprinkler System Myths

MYTH: When a sprinkler system actuates, all sprinklers on the system go off at the same time.

FACT: Each sprinkler has a heat-sensitive element with a predetermined temperature and sensitivity that responds to heat from a fire individually. Only those sprinklers in the immediate vicinity of the fire actuate and discharge water. It is not uncommon for only one or two sprinklers to go off in a fire.

MYTH: Sprinkler systems cause excessive water damage.

FACT: In most cases, water flowing from a sprinkler causes much less damage than a fire would cause in the absence of a sprinkler. A fire has the potential to completely destroy a building, and sprinkler systems have a solid record of performance in saving lives and property, with minimal water damage. It is also important to note that the water damage from a fire hose operated by the fire service during fire fighting operations in a non-sprinkled building could greatly exceed water damage from a sprinkler, because the rate of discharge from a fire hose is several times the rate of discharge from a sprinkler.

MYTH: Sprinkler systems don’t work.

FACT: Most studies of sprinkler system effectiveness show that sprinkler systems are between 98% and 99.8% effective in the control of fire. The majority of incidences regarding ineffectiveness of sprinkler systems are related primarily to the failure of building owners to keep sprinkler control valves in the open position.

MYTH: Automatic fire detection systems are an acceptable substitute for sprinklers.

FACT: Automatic fire detection systems do not control or suppress a fire and are not a substitute for an automatic sprinkler system. Detection systems have a good record of providing notification, but do not provide suppression.

MYTH: Accidental sprinkler discharge is common.

FACT: Sprinklers have an impressive history of reliable service in an emergency and discharge in the absence of a fire is very rare.

MYTH: Sprinkler systems cost too much.

FACT: Sprinkler systems are not prohibitively expensive. They usually are only a small fraction of the total cost for a building. It is not uncommon for an owner of a commercial property to recover the cost of the sprinkler system in 5 to 10 years through insurance rate reductions. A residential sprinkler system connected to a public water costs about $1.16 per square foot, less than the cost of most carpets.

MYTH: Sprinklers are ugly.

FACT: Sprinkler systems can be designed to maintain the beauty of a building. Pipes can be concealed above ceilings or behind soffits, and sprinklers can be selected from a wide range of aesthetic models. Ornamental and decorative sprinklers are available that allow concealment above the ceiling with only a small plate showing below the ceiling, with a wide range of factory-applied colors. While sprinklers can be concealed, management of a building may elect to use a visible presence of sprinklers as a sales tool to emphasize life safety in a building, especially hotels.

What is backflow?

Backflow is the undesirable reversal of the flow of water or mixtures of water and other undesirable substances from any source (such as used water, industrial fluids, gasses, or any substance other than the intended potable water) into the distribution pipes of the potable water system. There are two types of backflow conditions: backpressure and back siphonage.

Backpressure: Occurs when the user system is at a higher pressure than the supply water systems, allowing undesirable substances to be “pushed” back into the potable water system. Some causes are: booster pumps, potable water system connections for boilers, interconnection with other piping systems operating at higher pressures, or higher elevations in user systems such as high rise buildings.

Back Siphonage: Occurs when negative or reduced pressure exists in the supply piping allowing undesirable substances to be “drawn” into the potable water supply. Some causes are:

Undersized supply piping, supply line breaks, reduced supply system pressure on the suction side of an on-line booster pump, or sudden upstream high demand. An example of this is a child drinking milk with a straw. The child “sucks” on the straw and the milk flows up the straw and into the child’s mouth. What the child is actually doing is creating a sub-atmospheric pressure in his mouth and the atmospheric pressure (14.7psia at sea level) is pushing down on the surface of the milk and forcing the milk up the straw and into the child’s mouth.

Cross-Connection is defined as any actual or potential connection between a potable water system and any other source or system through which it is possible to introduce into the potable system any used water, industrial fluid, gas, or other substance other than the intended potable water with which the system is supplied. By-pass arrangements, jumper connections, removable sections, swivel or change-over devices and other permanent or temporary devices through which, or because of which, backflow can or may occur are considered to be cross-connections.

There are several different types of mechanical backflow prevention devices. An alternative to a mechanical device is a physical separation, or air gap. The air gap is a physical break in the system. Different types of mechanical devices are used in different situations (if there is backpressure or back-siphonage) and for different degrees of hazard. The degree of hazard is based on the fluid (or other substance) that may backflow into the supply piping system. The fluid may be toxic or nontoxic and could create a “non-health” or “health” hazard. A non-health (non-toxic) hazard cross-connection is any point in a water supply system where a polluting substance may come in contact with potable water aesthetically affecting the taste, odor or appearance of the water, but it is not hazardous to health. A health hazard (toxic) cross-connection is any point in a water supply system where a contaminating substance may come in contact with potable water creating an actual health hazard, causing sickness or death.

Fire Alarm Control Panels

Conventional

Traditional fire alarm panels installed prior to 1998 were conventional zone panels. In a zoned system, fire alarm devices in a common area or floor of a facility are connected to the same alarm initiating circuit. Each zone requires its own circuit conductor. This arrangement allows alarm annunciation to be reported by areas of the building to identify which device is in alarm. Conventional panels are often used in small facilities where a few zones can provide sufficient alarm annunciation.

Addressable

With the advent of microprocessors and digital electronics, addressable fire alarm control panels and devices have become more common than conventional systems for medium and large-sized facilities. They have become more cost effective in some small applications as well.

Addressable fire alarm systems use digital encoding and multiplex technology to more accurately identify alarm locations and device conditions. Each fire alarm device in a system is programmed with a unique address.

The fire alarm control panel is capable of communicating with a single address or a group of addresses depending on the functions required. The communication is often multiplexed over a common cable, sometimes referred to as the signaling line circuit (SLC). This arrangement significantly reduces the amount of cabling necessary to install the system. The communication channel allows two-way communication, thus enabling the fire alarm control panel to control as well as monitor fire alarm devices.

A significant component of addressable fire alarm system is the software programming necessary to make the system function correctly. The programming allows for flexible applications where you want to have specific control over the inputs and outputs.

The communication technologies employed in addressable systems allow for advanced features to accommodate sensitivity changes due to age and accumulation of dust prior to maintenance. These features are not available with the standard conventional system.

Fire Alarm Devices

Automatic Detection

Components of a fire consist of:

  • Smoke (particulate and aerosol)
  • Heat
  • Light Radiation
  • Fire detection devices are built to detect one or a combination of these components. While all components are necessary for a fire to exist, all components may not exist at a detectable threshold. Detectors will be selected that will detect the elements that may exist in a fire for the ambient conditions that are present. It also should be realized the similar non-fire components might exist in the same ambient conditions, which could cause unfavorable false alarm conditions.
  • Devices used for fire detection include smoke detectors, thermal detectors, flame detectors, fire-gas detectors, and other devices.
  • Smoke detectors sense visible or invisible particles of combustion generated by burning, smoldering, or the incipient stage of combustion. These devices fall into two categories — photoelectric and ionization.
  • Thermal detectors sense the high temperature or the temperature rise caused by a fire.
  • Flame detectors sense the radiation produced by a fire.
  • Fire-gas detectors sense the gases produced by a fire.
  • Other detectors sense some phenomenon other than smoke, thermal, flame, or fire-gas to detect a fire.

Smoke Detectors

There are three types of smoke detectors: Ionization, photoelectric, and combination.

Ionization

The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.

The ionization smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.

  • The alpha source causes the air within the smoke chamber to become ionized and conductive
  • As smoke particles enter the smoke chamber, the smoke particles attach themselves to the ionized air molecules and the air in the chamber becomes less conductive
  • When the air conductivity within the chamber drops below a predetermined level, the alarm is triggered

Advantages of Ionization Smoke Detectors:

  • Detects invisible products of combustion — It can detect fires that are in the incipient stage or detect other aerosol-type smoke products
  • Quick acting — Provides for earlier detection than other types of smoke detectors or thermal detectors
  • Disadvantages of Ionization Smoke Detectors:
  • May provide false detection if used where volatile solvents, conductive material dusts, or high humidity are present
  • Detects the presence of smoke only, not toxicity
  • Has a potential for high false alarm rate
  • Typical locations or hazards for ionization detection:
  • Clean rooms
  • Computer rooms
  • Mechanical air ducts
  • Locations where sensitive detection methods are needed

Photoelectric

A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.

Spot type photoelectric smoke detectors using the light obscuration principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.

Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.

Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.

Advantages of Photoelectric Smoke Detectors:

  • Sensitive to visual particles of smoke
  • Detects smoldering low heat fires
  • Provide early warning

Disadvantages of Photoelectric Smoke Detectors:

  • Early contamination by dust causing reduced sensitivity
  • Detects presence of smoke, not toxicity
  • Must be cleaned on a regular basis
  • Has a potential for high false alarm rate
  • Typical locations or hazards for photoelectric detection:
  • Office areas
  • Clean rooms
  • Raised floor spaces
  • Atriums and corridors
  • Meeting rooms
  • Computer rooms
  • Telecommunications rooms
  • Electrical equipment rooms
  • Sleeping rooms
  • Storage closets

Beam Detector

Beam smoke detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver. These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.

Advantages of Beam Smoke Detectors:

  • Cover a large area economically
  • Quick acting
  • Disadvantages of Beam Smoke Detectors:
  • Unobstructed LoS between the light source and the receiver
  • Correct alignment needs to be maintained
  • Typical locations or hazards for beam detectors:
  • High atriums
  • Manufacturing spaces

Air Sampling Smoke Detectors

For environments where detection of smoke is most critical, an air-sampling system provides the earliest possible detection. An air sampling or aspirating type fire detection system is a self-contained smoke detection package compromised of five primary components:

  • Air-sampling system
  • Aspiration system
  • Filter assembly
  • Detector
  • Control system

It uses a network of pipes to continuously draw air samples and direct them to a central smoke detector.

The system operates with a network of sampling pipes that extend into the protected area. The pipes are usually made of a thermoplastic material. An internal aspirator continuously draws air into the piping network. The systems use either a filter assembly or laser particle counting technology to filter out airborne dust and debris particles, which helps to eliminate false readings.
Typical locations or hazards for Air-Sampling smoke detectors:

  • Telecommunications areas
  • Computer rooms
  • Data centers
  • Hospitals
  • Clean room environments
  • Atriums
  • Cold storage areas
  • Power stations
  • Mines
  • Paper and timber mills
  • Museums
  • Art Galleries
  • Cathedrals

Thermal Detectors

Fixed Temperature

  • Fixed Temperature Thermal Detectors can respond to:
  • Fixed temperature limit
  • Rapid rate of change of the temperature in the protected area
  • Combination of these types of detection

Typical fixed temperature spot-type smoke detectors contain a bimetallic switch element that closes at a specified temperature limit. The switch is normally composed of two metals, each having a different temperature coefficient of expansion. As this bimetallic element heats the metal with higher coefficient of expansion, it causes the switch to bend or curve, closing the switch; thus indicating an alarm condition.

Line type thermal detectors are cables that detect heat along their entire length. A line type thermal detector may consist of two wires that are separated by an insulator. After the heat builds to a certain level the insulation melts, allowing the wires to touch and current to flow, initiating an alarm.

Bimetallic spot and coaxial style thermal detectors are self restoring. Fusible link and melting insulation types of line thermal detectors are not self-restoring.

Advantages of Fixed Thermal detection:

  • Lower cost than smoke detector units
  • More reliable than smoke detector units
  • Not affected by dusty or dirty environments
  • Minimal maintenance

Disadvantages of Fixed Thermal detection:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Rate of Rise

Rate-of-Rise Thermal Detectors measure the rate at which the air temperature changes during a fire event. Measuring the change in temperature provides a faster alarm response than measuring the temperature level in a space.

The rate-of-rise detector measures the change in the temperature of the space through the use of a differential pressure switch. This switch contains an air chamber separated for the air in the ambient space by a flexible diaphragm. As air in the ambient space changes temperature, the air pressure increases, creating a differential pressure across the diaphragm.

The air chamber is constructed with a calibrated leak so that normal temperature and pressure fluctuations within the room space adjust across both sides of the diaphragm and will not cause the alarm contacts to close. During a fire, the air temperature rises at a rate faster than normal, causing an increase on the room side of the diaphragme diaphragm. The leak cannot compensate, and therefore the diaphragm moves and closes the detector contacts.

Combination rate-of-rise and fixed temperature thermal detectors are also manufactured and have both technologies built in.
Advantages of Rate-of-Rise Thermal detection:

  • Responds faster than the fixed temperature detector
  • Not affected by dusty or dirty environments
  • More reliable than smoke detector units
  • Less expensive than smoke detector units
  • Minimal maintenance

Disadvantages of Rate-of-Rise Thermal detection:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Rate Compensated

Rate-compensated thermal detectors are devices that are designed to activate at a predetermined temperature in a space regardless of the rate at which the temperature in the space increases. This is accomplished by compensating for the thermal lag between the room temperature and the interior of the device.

Construction consists of an outer metal tube that expands at a fixed rate. Within this tube, alarm contacts close when a certain expansion distance is reached, but this expansion is opposed by another metal device.

At a slow rate-of-rise in temperature, the outer tube expands drawing the contacts closer together. The inner metal device exerts a counter force, keeping the contacts separated until the entire device has been heated to its rated temperature.

At a rapid rate-of-rise in temperature, the outer tube expands faster than the inner device can compensate. Therefore, the alarm contacts close when the entire device has been heated to a lower level, thus compensating for thermal lag.

Advantages of Rate Compensated Thermal detectors:

  • Responds accurately and positively to fire threats
  • Virtually eliminates false alarms
  • Not affected by dusty or dirty environments
  • More reliable than a smoke detector
  • Less expensive than smoke detector units
  • Minimal maintenance

Disadvantages of Rate Compensated Thermal detectors:

  • Slower to respond than smoke detectors
  • Will not detect products of combustion
  • Only suitable for protection of property

Flame Detectors

Flame detectors are used to detect the light radiation component of a fire. Typical detectors of this type detect the wavelength of either IR or UV or a combination of the two. These detectors are extremely fast acting and are used in areas where rapidly occurring fires or explosions could occur.

Advantages of Flame Detection:

  • Extremely fast acting

Disadvantages of Flame Detection:

  • Narrow field of vision
  • Expensive
  • Requires unobstructed field of view
  • Difficult to maintain

Typical Uses:

  • Fuel loading docks
  • Industrial process spaces
  • Other hazardous areas where a fast developing fire could occur

Fire-Gas Detectors

These detectors respond to the various gases produced during the combustion process.

  • Carbon monoxide
  • Carbon dioxide
  • Steam
  • Other elements

The Fire-Gas detector employs two types of technology to predict the fire. One method uses a semiconductor material that changes the metals conducting potential in a fire situation. The other method uses a catalytic element encased in an aluminum bead.

Advantages of Fire-Gas Detection:

  • Detects products of combustion
  • Sensitive enough to detect levels of gases produced between the occurrences of detectable particulate levels and detectable heat levels
  • Detects gases prior to reaching lethal levels

Disadvantages of Fire-Gas Detection:

  • Can be prone to false alarms
  • Must be mounted at a low level, leaving it susceptible to damage
  • Can be poisoned
  • Not suitable for areas where CO and CO2 and produced as part of the functions within the area
  • Cannot be considered as a universal replacement for smoke and/or thermal detectors
  • High cost
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