The most important part of a firefighter's respiratory system protection is the quality of the air contained in their SCBA cylinder. And like the old computer adage of "garbage in, garbage out" having cylinders full of quality air is paramount. And this ultimately comes down to the fill station.
There are several organizations that promulgate standards that have influence over SCBA fill stations and containment units. These include the National Fire Protection Association (NFPA 1989: Standard on Breathing Air Quality for Emergency Services Respiratory Protection, 2008 and NFPA 1500: Standard on Fire Department Occupational Safety and Health Program); the Occupational Safety and Health Administration; UL; and the Compressed Gas Association.
When most folks say, "SCBA fill station" they are referring to a system composed of:
- High-pressure air compressor
- Electrical motor
- Air-purification system
- Refill station
- Storage system
- All operating controls and appliances.
Most of the major fire service equipment vendors can an integrated system (all components in one cabinet and designed to work in concert with each other), or a system of individual component parts.
One advantage of the integrated system is that a purchasing department knows that the components will work together; and if repairs are needed there is only one point of contact to deal with, the vendor that sold the system. A downside is that the failure of one of the components can render the entire system inoperable.
One advantage to a system of components is that the failure of one component, while it may render the system inoperable, might be fixed more quickly and at a lower cost — or replaced completely if that's more cost effective. A downside could be that the department may have to deal with several vendors.
For the heart of the system, look for an air-cooled, reciprocating four-stage compressor powered by at least a 10-horsepower motor. The compressor should be designed for continuous duty at 6,000 psi working pressure with a charging rate of at least 14 scfm (standard cubic feet per minute). The compressor must not vent oil-contaminated air to the atmosphere.
There will need to be room for unrestricted cooling airflow to the compressor and adequate access for operation and maintenance. Most compressors are designed to work indoors within a temperature range of 40°F to 115°F. Addresses these space issues during planning.
Make sure that each stage of compression, except for the first stage, has a separator and that a coalescing separator is installed after the final stage of compression. Each of the separators must also have an automatic condensate drain system (ACDS) to remove condensate from the compressor before it can extend into the entire system.
Besides the contamination to the air coming from the compressor, condensate can reduce the effectiveness or destroy compressed air components such as lines, filters and storage cylinders.
The ACDS should also unload the compressor — make sure that all condensate is out of the compressor — on shutdown so that the next time the compressor starts up it does so unloaded. Manually operated valves should be included to override the ACDS's automatic operation for testing and maintenance purposes.
Electrical control and instrument panel
Some of the more significant advances in SCBA refill systems have come from innovation in the electronic controls. The electrical control system should include components that are approved by UL, the National Electrical Manufacturers Association or the International Electrotechnical Commission.
Specify a system with an "on/off" selector switch that, when in the "on" position, automatically starts and stops the compressor motor to maintain the system's operating pressure between the high and low set points of the final pressure switch.
Maintaining proper compressor oil pressure is critical for the system's performance and longevity. Today's systems monitor the oil pressure using a pressure switch and pressure gauge; should the compressor's oil pressure drop below the factory preset value during operation, the compressor should shut down and a fault light on the instrument panel should illuminate.
Finally, the discharge line of the final stage of compression should have a temperature switch that automatically shuts down the system when it detects that the final stage discharge temperature has exceeded the tamperproof set point.
The quality of the breathing air in SCBA cylinders is directly dependent upon the air-purification system. The high-pressure breathing air must meet or exceed the requirements of CGA Pamphlet G-7 (Grade “E”), Compressed Air for Human Respiration, ANSI/CGA G-7.1, Commodity Specification for Air, Grade E and Grade D, and any other recognized standards for SCBA breathing air.
Most systems achieve this level of air purification through the use of:
- A mechanical separation of condensed oil and water droplets.
- Adsorption of vaporous water using a desiccant (a hygroscopic substance that induces or sustains a state of dryness [desiccation] in its local vicinity in a moderately well-sealed container).
- Adsorption of oil vapor and elimination of noxious odors using activated carbon.
- Conversion of carbon monoxide to breathable levels of carbon dioxide via a catalyst.
The system should use replaceable cartridges in the purification system; replacing those cartridges should not require you to disconnect any of the system piping. The system should also include safeguards that eliminate the possibility of its operating without the cartridges being installed or being installed improperly.
Cylinder fill control station
This part of the system's dashboard should enable you to control the direction of breathing air produced by the compressor into individual SCBA cylinders or to storage (the high-pressure storage cylinders, or, Cascade system). At a minimum, the air storage system should consist of four interconnected storage banks and be designed to fill two SCBA cylinders either independently or simultaneously.
The cylinder fill stations should include a minimum of three fill hoses — two with connectors for both 2,216-psi and 3,000-psi SCBA cylinders; and one 4,500-psi connector necessary for refilling SCUBA cylinders. Ensure that each fill hose is equipped with a bleed valve and SCBA fill adapters that can accommodate the cylinders listed above.
The control panel should include, at a minimum:
- An automatic storage bypass system
- A manual control valve and pressure gauge for each storage bank
- An adjustable regulator for SCBA cylinder fill pressure with a pressure gauge for inlet and regulated pressure, and a relief valve to protect the SCBA cylinders from overfilling
- A manual control valve and pressure gauge for each fill position, and provisions for factory or field modification to allow a different fill pressure at each fill position.
The system you specify must include a mechanism to contain the cylinder and any fragments of the cylinder and vent the expanding air away from the operator in the unlikely event of a cylinder rupturing while being filled. Today's systems are designed to totally enclose the SCBA cylinders during the refilling process and include a safety interlock system that will prevent refilling SCBA cylinders unless the fill station door is closed and secured in the closed position.