Guide to respiratory protection
The choice of using a filter must be taken to provide the optimal conditions of safety for the user. The protection factor is dependent on the air tightness of the face piece (masks for use with filters), or complete equipment such as powered air purifying devices.
1 Know your toxicity levels
Chemical formulas are complex. The same formula can have several names. The only reliable reference is the CAS.
CAS: ask your provider for the toxicity CAS number. Get the international safety record: it will allow you to check the potential risks, and the interactions to avoid.
This will provide several levels:
- WEL: the Workplace Exposure Limit over a period of 8 hours, in ppm (parts per million) or mg/m 3 (concentration).
- TLV: the short term Threshold Limit Value (10-15 minutes).
- ILD: Immediate Lethal Dose: this requires the immediate evacuation of the area.
The international safety record also provides information on:
- The chemical form of the product (gas, vapour, dust, depending on the temperature, humidity, its evolution, its interactions).
- Self-warning properties (odour, colour).
- The associated risks (eye, skin, carcinogen, explosive).
2 Know the concentration of a toxic substance in the environment concerned
- In ppm or mg/m 3, for example 7.500 ppm.
3 Choose the right protection: mask, half-mask, air supply or assisted breathing?
The Nominal Protection Factor (NPF) is required for selection of the right product, for example:
Hypothesis: The OEL of the product is 10 ppm and external concentration is 7500
External concentration = 7500/10 = 750 OEL
The NPF is 750.
The NPF is also defined in the standard as the inverse of the total inward leakage.
What are the NPFs of our face shields?
An NPF of 750 is between 500 and 1000, so we must choose a protection with NPF 1000
- Either a full mask with a P3 filter.
- Or a full mask with a combined gas/particle filter.
- Or an assisted powered air purifying respirator.
The more a toxic substance is declared dangerous, the more the choice must be careful and approved. Again, one must be sure before using a filter system:
- To have validated the minimum oxygen level.
- To know the self-warning properties.
4 If there is a skin or eye hazard
It identifies the choice of eye protection as a priority (conjunctivitis, irritation, redness, burning etc.).
Following contact with the gas or vapour
- A full-face mask is mandatory.
Following contact with a liquid or projection
- A half mask combined with a pair of safety goggles suitable for work with the toxic substance is recommended.
When in doubt, choose a full-face piece
The eye risk is a major functional risk. Remember, it is very difficult to escape a risk without one's eyesight.