Wheeled Fire Extinguishers Over the past 40 years, the demand for transportation, storage, and handling offlammable fuels that fall under the fire protection classification of "High Hazard" has increased drastically. This has often occurred at a faster rate than most fire protection requirements or coverages. Recent trends toward automation and workforce reductions have placed additional demands upon fast response types of fi re fighting equipment. With fewer people available to respond to emergency situations where higher fire loads exist, portable wheeled fire extinguishers that provide a quicker, more effective extinguishment solution than water, should be utilized. Portable wheeled fire extinguishers have been around for well over 50 years and were, in those early years, referred to as "Wheeled Engines". The first true market niche for this equipment was established during the early 1940s when it was used to protect military airport ramps. Wheeled extinguishers can be easily operated by one person and are considered to be portable extinguishers falling under The National Fire Protection Association's Standard NFPA-10. The portable "wheeled" units are differentiated from "hand portable" types often simply on the basis of their capacity or total weight. For example, the portable extinguisher design standard for dry chemical extinguishers ANSI/UL-299 specifies that hand portable models not have a t otal charged gross weight exceeding 60 pounds. Wheeled units are available in a variety of model sizes that feature extinguishing agents such as carbon dioxide, dry chemical, halons, dry powder, and AFFF-type foam pre-mix solutions. Agent capacities of 30 to 350 pounds are offered, with many of the smaller-sized units sometimes being glorified hand portables on wheels marketed to meet minimum high hazard requirements or for added ease of mobility. The primary fire protection value of wheeled fire extinguishers is in t heir ability to: Contain greater extinguishing agent capacities Deliver higher agent flow rates Provide additional fire fighting ranges Extend discharge times. These unique fire fighting characteristics are also extremely valuable during emergency situations in Page 1 of 4 Wheeled Fire Extinguishers 20/05/10 http://www.reliablefire.com/portablesfolder/wheeledunits.html
Over the past 40 years, the demand for transportation, storage, and handling of flammable fuels that fall under the fire protection classification of "High Hazard"has increased drastically. This has often occurred at a faster rate than most fireprotection requirements or coverages. Recent trends toward automation and work force reductions have placed additional demands upon fast response types of firefighting equipment. With fewer people available to respond to emergencysituations where higher fire loads exist, portable wheeled fire extinguishers thatprovide a quicker, more effective extinguishment solution than water, should beutilized.
Portable wheeled fire extinguishers have been around for well over 50 years and were,
in those early years, referred to as "Wheeled Engines". The first true market niche forthis equipment was established during the early 1940s when it was used to protectmilitary airport ramps.
Wheeled extinguishers can be easily operated by one person and are considered to be
portable extinguishers falling under The National Fire Protection Association's StandardNFPA-10. The portable "wheeled" units are differentiated from "hand portable" typesoften simply on the basis of their capacity or total weight. For example, the portableextinguisher design standard for dry chemical extinguishers ANSI/UL-299 specifies that handportable models not have a total charged gross weight exceeding 60 pounds.
Wheeled units are available in a variety of model sizes that feature extinguishing
agents such as carbon dioxide, dry chemical, halons, dry powder, and AFFF-typefoam pre-mix solutions. Agent capacities of 30 to 350 pounds are offered, with manyof the smaller-sized units sometimes being glorified hand portables on wheelsmarketed to meet minimum high hazard requirements or for added ease of mobility.
The primary fire protection value of wheeled fire extinguishers is in their ability to:
providing assistance to various rescue and evacuation efforts.
Basic Extinguisher Operation Principles
There are basically four operation principles in which wheeled extinguishers are designed andmanufactured.
Self-Expelling: These models typically contain theextinguishing agent within a single high-pressure cylinder.When the cylinder valve is opened, the extinguishing agent'sown vapor pressure forces the agent to travel up a pick-up tube,through the operating valve and out the discharge hose nozzlevalve onto the fire. This principle is primarily limited to carbondioxide wheeled models which are not equipped with pressuregauges to indicate charge status.
Stored Pressure: With this principle,the extinguishing agent and expellant
gas source (normally superpressurized nitrogen) is containedwithin the same cylinder. Uponactuation of an operating valve,internal pressure forces theextinguishing agent up the pick-up
tube, through the operation valve and out the discharge hose nozzlevalve on to the fire. This configuration of hardware is normally theleast expensive.
Pressure Transfer: This concept consists of separate extinguishing agentand expellant gas cylinders. The expellant (normally compressed nitrogen) iscontained within a sized high-pressure cylinder intended to properlypressurize and discharge the total contents of the agent cylinder. Uponopening of the expellant gas cylinder operating valve, expellant gas istransferred through a special gas distribution tube assembly that fluidizes andpressurizes the agent cylinder to a pre-determined head pressure. Thispressure permits the extinguishing agent to travel up the agent tank pick-uptube and out the discharge nozzle valve on to the fire. This concept is less susceptible tovibration pressure losses in rugged and abusive environments. The separate unpressurizedagent cylinder allows simple agent examination and quick recharges in the field.
Regulated Supply and Demand: While similar to the pressure transfer principle in mostways, this concept utilizes a much larger volume expellant gas cylinder source and a pressureregulator. As the extinguishing agent is discharged, the regulator will flow and meter
additional expellant gas pressure to the agent tank, providing a more consistent operatingpressure. This ensures stable agent flow rates and ranges throughout the fire fightingevolution. While usually higher priced, many fire hazards justify the additional cost associatedwith the regulator and larger gas cylinder necessary on these models.
Extinguisher Options
There are a large variety of options available to wheeled extinguishers, with the nozzle design andwheel configuration being two of the most often misunderstood and incorrectly applied.
Wheel diameters of 16 to 44 inches are commonly offered in various widths andfinished rolling surface bases. The large diameter wheel types will provide superiormobility and ease of operation over uneven surfaces like potholes, sidewalks orsmall steps. Wide 6-inch wheel bases provide additional versatility on soft surfaces
such as loose sand, gravel or sod. When spark reduction or the marking of floorfinishes is a consideration, the pneumatic, semi-pneumatic and rubber-banded wheels should beutilized rather than the steel base types. Because pneumatic wheels will absorb some surface shock,they generally deliver the best unit ride and are often selected for large airport ramp areas wheretowing operations exist. The semi-pneumatic and rubber-banded wheels eliminate potential flatproblems in and around areas where sharp objects may be present.
Before purchasing any unit, always check to ensure the overall width of the unit, under its specificwheel option configuration, will fit through any necessary aisles or door passageways.
The nozzle selection of the wheeled extinguisher directly contributes to various operationcharacteristics such as the discharge range, pattern, velocity, flow rate and fire rating.
Range information published by manufacturers can often be somewhat misleading. The focus hereshould be on the unit's "effective range" established through actual fire-fighting evolutions, subjectto thermal up-draft factors. Different internal nozzle bore designs provide various agent streampatterns, flow rates and velocities. Discharge characteristics should be properly matched to theparticular fire hazard. For example, the venturi designs generally provide higher velocities andranges at lower agent flow rates, which work well on large class "A" fire applications. On the otherhand, cone-type nozzle designs normally reduce agent velocity for a softer discharge, making themideal around fuel-in-depth situations where splashing of fuels in, and around, confined areas couldpresent problems to firefighters.
Equipment specifiers should also keep in mind that the portable extinguisher class "B" rating systemis based on minimum discharge times and only one type of fire configuration. For the manufacturersto obtain higher and more impressive ratings, they must increase discharge times by cutting back agent flow rates, which is detrimental to the extinguishment of many other common industry class"B" fire configurations. Agent flow rates become critical in obstacle, gravity, 3-dimensional andpressure fire configurations. The NFPA 10 standard recognizes this and specifically states under
several such hazard areas that "The system used to rate extinguishers on class "B" fires is not directlyapplicable to these types of hazards." For most wheel unit applications, higher attention to the agentflow rates over extinguisher ratings is in order. Most manufacturers can provide recommendationsand furnish support data.
Maintenance
Wheeled fire extinguishers, like hand portable models, are mechanical devices that require periodicservice for optimum performance and reliability. Both OSHA and NFPA requirements specifymaximum extinguisher inspection intervals of 30 days and for maintenance to be performed at leastannually.
Training
When properly selected and maintained, wheeled fire extinguishers provide an exceptional firefighting resource for the high risk industries of today. For companies to benefit and reap the fullpotential of these extremely effective units, training programs properly designed to demonstrate andfamiliarize operators with their impressive capabilities should also be regularly conducted.
The above article was originally published by NAFED , the National Association of Fire Equipment Distributors.
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