Breathing Air Systems (OSHA Grade D)
Compressed air, commonly called Industry’s fourth utility, is the most common utility used in a typical industrial facility. Compressed air is used in more than 70 percent of all manufacturing activities including supplying breathing air to personnel using supplied air respirators. Hazardous breathing conditions exist in many routine industrial operations, such as chemical manufacturing, hospitals, abrasive blasting, paint spraying, industrial cleaning, and arc welding. In these and other operations that introduce contaminants into the workplace, supplied-air respirators, air filtration systems and carbon monoxide monitors are frequently used for worker protection.
OSHA Standard 29 CFR 1910.134(i)(1)
These “breathing air” systems are designed to meet Occupational Safety and Health Administration (OSHA) Standard 29 CFR 1910.134(i)(1) which states: “Compressed breathing air shall meet at least the requirements for Grade D breathing air described in ANSI/Compressed Gas Association Commodity Specification for Air, G-7.1-1989, to include:
- Oxygen content (v/v) of 19.5% – 23.5%;
- Hydrocarbon (condensed) content of 5 milligrams per cubic meter of air or less;
- Carbon monoxide (CO) content of 10 parts per million (ppm) or less;
- Carbon dioxide (CO2) content of 1,000 ppm or less; and
- Lack of noticeable odor”
Four Common Compressed Air Contaminants
There are four main types of compressed air contaminants of concern in a compressed breathing air system.
- Carbon Monoxide – Carbon monoxide (CO) is a common toxic contaminant in compressed air. It enters the breathing air system through the air intake, or is produced by overheating of piston type air compressors. The air intake must be placed away from engine exhaust or other sources of carbon monoxide. CO poisoning can cause headache, shortness of breath, dizziness, nausea or vomiting, confusion and loss of consciousness.
- Water/Water Vapor – Air contains moisture, which is drawn into the air compressor and enters the air stream as a vapor. As compressed air flows through the system, it cools, causing the vapor to condense in the facepiece or helmet. Moisture combines with oil and solid contaminants to form sludge, which can clog or damage system components. Water also causes rust in pipelines, and can freeze in cold weather to block air flow.
- Oil/Oil Mist – Oil is a major contaminant in systems using lubricated air compressors. In reciprocating compressors, lubricating oil applied to cylinders causes small droplets by the shearing action of the piston to enter the air system as a mist. Oil mist can cause breathing discomfort, nausea, pneumonia, and create unpleasant taste and odors.
- Solids – Solids generally enter the system through the air intake. However, some materials may be introduced by the air compressor itself. In non-lubricated compressors, teflon, carbon and other materials are used as lubricants. Frictional wear can cause particles from these materials to enter the air stream.
Air Compressor Location Selection
Oil-lubricated air compressors are a common source of supplied breathing air. These compressors are placed in a wide range of ambient air conditions. Common contaminants in the ambient air of typical work areas may contain carbon monoxide, water vapor, oil and dirt. An important consideration, when providing safe compressed breathing air, is the location of the air compressor. OSHA 1910.134(i)(5) states, “the employer shall ensure that compressors used to supply breathing air to respirators are constructed and situated so as to prevent entry of contaminated air into the air-supply system.”
The air compressors in a large industrial facility are often located in a dedicated room or separate building from where the actual supplied-air respirators are being used. It is important to locate the compressor away from hazardous areas where the air intake could be easily contaminated, such as in truck/vehicle loading areas where carbon monoxide is likely to accumulate or areas where chemicals and solvents are used or stored, or where heaters or combustion equipment are used.
Grade D Compressed Air Filtration System
A compressed air filtration system that removes oil, water, solid particles and odors from supplied breathing air is an important component in supplying Grade D breathing air and ensuring the safety of personnel using compressed air. ENMET’s AFS-50 air filtration system incorporates a unique three-stage filtration concept which utilizes a prefilter, high-efficiency coalescer filter and charcoal adsorber element. The compressed air passes through the prefilter/coalescer, a two-stage filtering device, which removes oil, water, and solid particles from the compressed air. The prefilter extends the life of the coalescer and adsorber filter elements. The coalescer is a high-efficiency filter that removes oil mist and fine (sub-micron) particles. Once the compressed air is filtered through the prefilter/coalescer it then passes through the adsorber filter which removes unpleasant odor and taste. The AFS-50 manifold has a maximum capacity of 50 CFM and is equipped with four outlet ports each supplied with a quick-disconnect. The system provides uniform air distribution to four supplied-air respirators and a fifth quick disconnect can be used for connecting a carbon monoxide monitor or an additional respirator.
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