Grade-D breathing air

Grade-D breathing air is the minimum compressed-air purity for supplied-air respirators under OSHA 29 CFR 1910.134, with the underlying spec written by the Compressed Gas Association as CGA G-7.1 / ANSI Z86.1. Six contaminants are limited: oxygen 19.5-23.5 percent, water (at point of use), condensed hydrocarbons less than 5 mg/m3, carbon monoxide less than 10 ppm, carbon dioxide less than 1,000 ppm, and a defined “no objectionable odor.”

What it is

A grade-D system pairs an appropriate compressor (typically oil-free or with high-efficiency oil-removal filtration), refrigerated or desiccant drying, particulate and coalescing filtration, an activated-carbon bed for hydrocarbons and odors, and a CO monitor with alarm. All of these are sized to the worst-case demand of the connected respirators.

Why it matters

Workers wearing supplied-air respirators are downstream of a single failure point: the compressor and treatment train. CO from a generator drawing through the compressor intake, oil migration from a worn separator, or hydrocarbon ingestion from a parking lot can all be fatal at concentrations that would be unremarkable in plant air. Grade-D is the auditable floor that keeps a system out of OSHA citation territory.

How it is used in our catalog

The breathing-air compressor archive lists units rated and packaged for grade-D and SCBA-fill service. Each entry confirms CO monitor compatibility, activated-carbon bed sizing, and oil-removal class. The dryer catalog covers the drying half of the grade-D train.

Common questions

Is grade-D the same as grade-E?

No. Grade-E is a higher-purity spec used for SCBA cylinder filling and some medical applications, with tighter hydrocarbon limits.

Do I need a CO monitor on every grade-D system?

OSHA does not mandate one if the compressor is oil-free and the intake is in confirmed clean air, but most installations include a CO monitor with alarm and shutdown as a basic safety practice.