Oil-Free Air Vs. Breathing Air
The two often get mixed up, but they’re not the same thing and the filtration requirements are quite different.
1. Oil-Free Air
“Oil-free” simply means the compressed air has no oil contamination from the compressor (typically from an oil-free compressor design).
- It does NOT guarantee the air is safe to breathe
- It may still contain:
- Water vapour
- Particulates (dust, rust)
- Microorganisms
- Oil vapour from ambient air intake (yes, even oil-free compressors can draw in hydrocarbons)
Clean for processes, not necessarily safe for humans= Oil-free
2. Breathing Air
Breathing air is a regulated standard of air quality safe for human respiration, such as BS EN 12021.
This standard strictly controls:
- Oxygen content
- Carbon monoxide (CO)
- Carbon dioxide (CO₂)
- Oil (liquid + vapour)
- Water (dew point)
- Odour/taste
In short: breathing air = medically safe air
Key Differences
Oil-Free Air vs. Breathing Air
| Feature | Oil-Free Air | Breathing Air |
| Oil contamination | None from compressor | Extremely low (strict limit) |
| Moisture control | Basic drying | Tight dew point control |
| CO / CO₂ control | Not controlled | Strict limits |
| Filtration level | Moderate | Very high / multi-stage |
| Safe to breathe? | No | Yes |
Filtration Requirements
For Oil-Free Air (Typical Setup)
You still need filtration, even with an oil-free compressor:
Pre-filter (particulate filter): Removes dust, rust, debris (~1 micron)
Coalescing filter: Removes water aerosols and fine particles (~0.01 micron)
Dryer (refrigeration or desiccant): Controls moisture (e.g. +3°C or -40°C dew point)
For Breathing Air (Typical Setup)
This is where it becomes much more stringent:
Pre-filtration (particulate + coalescing): Removes bulk contaminants
High-efficiency coalescing filter: Removes fine oil aerosols and particles
Desiccant dryer: Achieves low dew point (often -40°C or better)
Activated carbon filter / tower: Removes oil vapour, hydrocarbons, odours
Catalytic converter (if required): Converts carbon monoxide (CO) into CO₂
Final sterile / dust filter: Ensures clean delivery air
Monitoring system: Continuous CO and oxygen monitoring (critical for compliance)
Important Reality Check
Even if you start with an oil-free compressor:
- You still need full breathing air treatment to meet BS EN 12021
- The biggest risks (CO, hydrocarbons, moisture) come from ambient air, not just the compressor.
Simple Way to Think About It
- Oil-free air = engineering cleanliness
- Breathing air = life safety standard
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