Save your breath - a filter is not for life but your lungs are
October 1st 2007

New research suggests that the health and safety of

employees working with reusable respirators is

being put at risk due to a lack of understanding –

both by users and their employers – of the need to

regularly change the filters attached to the mask, says

3M

In some cases, companies may have inadequate systems in

place to ensure that filters are changed regularly, while in

other organisations a lack of proper training can leave

employees unsure of when a change should be made.

Respirators with changeable filters are used across a wide

range of industries, with the filters used falling into three

categories:

Particle filters: These protect against particles such as

dust, mists and fumes, aerosols, mould and bacteria

Gas and vapour cartridge filters: These protect against

gases and vapours, with different kinds of cartridge filters

available for different types of gases

Combination filters: These protect against both particles

and gases and vapours, with different combinations

available depending on the gas or vapour present in the air.

Filters are colour coded. Gas and vapour and combination

filters have bands using the performance colour coding from

the European Standard. Different letters and colours indicate

the groups of gases and vapours that the filters are

designed to protect against.

There are a number of methods which can be used to

determine when the life of a filter is at its end:

Particle filters will eventually become clogged and their

breathing resistance will increase

Gas and vapour filters will become saturated and

"breakthrough" will occur.

This is indicated by the

wearer smelling or tasting

traces of the contaminant.

It is not advisable to

routinely rely on detecting

smell or taste, but to change

filters before breakthrough.

Company risk assessments

and health and safety

procedures should specify

timescales for regular filter

changes.

If there are no existing

change schedules, companies

with a stable concentration

of contaminant can establish

them by taking their typical

breakthrough time and

applying a safety margin.

With gas and vapour filters it

is particularly important not

to rely on breakthrough

alone, since by this point the

effectiveness of the filter has

already been reduced.

Continuing to use a clogged

particle filter will lead to discomfort and increase the

chance of face seal leakage. Clogged filters should never be

cleaned.

For substances with low warning properties – those with

little or no smell or taste, such as isocyanate in some paints

– supplied air respiratory protective equipment should be

used rather than a mask and filter, since breakthrough

cannot be detected with this type of substance which could

lead to serious consequences.

Even when a filter change schedule has been established

gas and vapour filters should only be used against

contaminants with good warning properties. This allows

wearers to detect breakthrough if conditions have changed

and the filter has become saturated before its scheduled

change. In normal use, the service life of a gas and vapour

cartridge filter is affected by many factors. These include

concentration and type of contaminants, breathing rates

and humidity levels, as well as other factors.

The need to ensure that the user of the respirator has the

training and knowledge they need to make these crucial

decisions about when to change filters is highlighted by

new research carried out on behalf of 3M.

The survey analysed responses from 553 companies which

use respirators across the full range of industry sectors. Of

these companies:

27 percent manufacturing

10 percent in construction

11 percent in automotive

6 percent in chemicals

The results showed that the majority of employees wear half

or full face masks for less than one hour at a time. 71

percent said they had procedures in place for regularly

checking their respirator for signs of wear and tear, and

40% of respondents incorporate checks into other regular

procedures – 25% use written record cards, and 16% mark

the respirator to indicate the date it was first used to show

its age.

In the majority of cases (63%), it is the employee who

decides when to replace the respirator, with 35% of such

decisions made by the company health and safety function,

and 13% made by maintenance personnel.

When it comes to replacing filters, the onus is even more

on the employee, with 76% of users deciding when to

replace filters, compared to 28% of decisions made by a

supervisor, 25% by health and safety, and 18% inline with a

set company policy - companies had the option to select

more than one method, suggesting that checks and balance

are in place across multiple functions in many organisation.

The survey also asked for a list of factors driving the

decision to change filters. 40% mentioned when breathing

resistance increases, 40% when the hazard can be smelt or

tasted, and 30% in accordance with company procedures.

However, 43% of respondents stated that one of the factors

used to decide when to change the filter is whether it looks

old, dirty, or worn. This method is misleading as filters do

not always need changing when they are dirty, some

environments mean that the filters will look dirty very

quickly but still be performing.

These results emphasise the need for training backed by

robust health and safety

procedures.

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