| The requirements for Grade D breathable air include: | |
| Oxygen | 19.5-23.5% |
| Hydrocarbons (condensed) in mg/m3 of gas | 5 mg/m3 max. |
| Carbon monoxide | 10 ppm max. |
| Carbon dioxide | 1,000 ppm max. |
| Odor | No detectable odor |
| No toxic contaminants at levels that make air unsafe to breathe. | |