A gas mask filter – just like any other filter – has a limited shelf life, which is called breakthrough time. It occurs when the carbon granules cannot absorb a pollutant (toxic gas) anymore. As a consequence, the user cannot breath clean filtered air any longer.
A gas mask filter features a carbon-made micro porous structure with a very large absorption surface in a small cartridge. Thanks to this technology, filters include less carbon (from 220 to 230 mL), which also reduces weight and breathing effort. Tables with theoretical shelf lives are available but shall not be taken strictly. Indeed, the shelf life of a gas filter depends on several factors.
Factors impacting gas filter shelf life
- Gas concentration: higher concentrations will quickly accumulate the pollutant on carbon, hastening the breakthrough time.
- Filtered air flow or breathing rate: theoretical shelf lives are set on a flow of 30 liters of air per minute. A higher breathing rate will reduce the breakthrough time.
- Temperature: if operation temperature rises, the gas filter shelf life will decrease
- Relative humidity: for VOCs, high humidity will accelerate the breakthrough time. The opposite effect also occurs for some gases like ammonia (nh3) or hydrogen sulfide (h2s)
- Shocks: shocks on a respirator cartridge have harmful effects. As they pack granules shocks will reduce their absorption power
Gas mask filter shelf life calculation
There is a formula to calculate a gas filter shelf life:
Shelf life = (1 000 000 x filter capacity*) / (breathing rate x gas concentration)
* the filter capacity depends of the manufacturer. Information is available on technical sheets.
Gas mask filter breakthrough time
Gas filters for negative pressure respirators
Test preamble: test gas concentrations for gas masks (negative pressure) are set at 1.000 ppm (0,1% volume) for class 1 and 5.000 ppm (0,5% volume) for class 2.
Spasciani DIN Rd40 filters fit most gas masks that are EN 148-1 approved, with a universal thread of 40 mm.
| Filter type | Test gas | Breakthrough time | |
|---|---|---|---|
| Class 1 | Class 2 | ||
| A | Cyclohexane (C6H12) | 70 min | 35 min |
| B | Chlorine (Cl2) | 20 min | 20 min |
| B | Hydrogen sufide (H2S) | 40 min | 40 min |
| B | Hydrogen cyanide (HCN) | 25 min | 25 min |
| E | Sulfur dioxide (SO2) | 20 min | 20 min |
| K | Ammonia (NH3) | 50 min | 40 min |
Gas filters for powered air purifying respirators
Test preamble: Test gas concentrations for PAPR masks are set at 500 ppm (0,05% volume) for class 1 and 1.000 ppm (0,1% volume) for class 2.
| Filter type | Test gas | Breakthrough time | |
|---|---|---|---|
| Class 1 | Class 2 | ||
| A | Cyclohexane (C6H12) | 70 min | 35 min |
| B | Chlorine (Cl2) | 20 min | 20 min |
| B | Hydrogen sufide (H2S) | 40 min | 40 min |
| B | Hydrogen cyanide (HCN) | 25 min | 25 min |
| E | Sulfur dioxide (SO2) | 20 min | 20 min |
| K | Ammonia (NH3) | 50 min | 40 min |
Special filters breakthrough times (AX et Hg-P3)
| Filter type | Test gas | Gas concentration | Breakthrough time |
|---|---|---|---|
| AX | Isobutane (C4H10) | 2.500 ppm | 50 min |
| Hg-P3 | Mercury vapor | 1,6 ml/mg | 100 hours |
Theoretical breakthrough times source: Scott Safety.