Gases are substances that in the normal environment conditions are in aeriform phase.
Typical examples are: Oxygen, Nitrogen, carbon dioxide.
Vapours are fluids, produced by transformation from a solid or liquid state to an aeriform state, through evaporation or boiling processes. Typical examples of vapours asolvents like: acetone, toluol and hexane.

Filters with activated charcoal are used for the protection against hazardous gases and vapours; they are modified to have a selective absorption of the various contaminants.
The main types of filters, fixed by the EN 14387 Standard, are:

The knowledge of the chemical nature of the contaminants is necessary to choose the right protection against gases and vapours. Use the tables supplied by BLS to select which type of filter is required for particular substances.
The general principle of the gas and vapours protection with the use of activated charcoal filters is that the contaminant olfactory threshold is inferior to the TLV. This precaution allows the worker to feel the filter exhaustion in terms of security.

It’s very useful to underline that, in the protection against gases and vapours, the filters guarantee total efficiency until they are not saturated by the contaminants.
Consequently in the standards there is the concept of filter capacity. The standard provides three levels of capacity filters: low, medium and high.
Therefor, regarding protection against gases and vapours, the total filter efficiency is determinate by the mask type and not by the filter used.

Though the filter efficiency is about 100%, the filter life grows with the filter charcoal capacity, as a high amount of charcoal will require a greater
amount of contaminant to reach its saturation. On the other hand, both the volume and the weight grow and the breathing resistance increases.

When in the environment at the same time both gases and vapours and dust are present, it is necessary to use a combined protection, mounting a suitable particle pre-filter.