3M: Fit tests and the science behind them

Checking that a tight-fitting mask provides proper sealing to the wearer's face has long been considered a recommended practice as part of a general respiratory protection program. Tight-fitting masks include disposable masks, half-masks and full-face masks, including those that are part of a motorised breathing device or an air-tight mask. This guide includes information on some fit test methods and some test solutions 3M supporting an adjustment test regime.

When to perform the fit test

Recommended practice suggests conducting adjustment tests:

• Before the mask is distributed to users.

• For all wearers of strap-on adjustment masks who have not previously been tested for adjustment The adjustment tests should be repeated at the appropriate time, such as:

• If the user loses or gains significant weight, has had major dental surgery or suffers a major facial injury

• If a different size or model of PPE is specified

• At regular intervals as defined by national guidelines or company guidelines The fit test should be done in addition to the seal check.

Fitting test methods

There are two (2) main fit test methods available:

• Qualitative adjustment test

• Quantitative adjustment test

During both test methods, it is essential that the subject is free of facial hair and other elements that may interfere with facial sealing. Users with facial hair or budding beard (even with a few days of growth) should not wear a tight-fitting mask.

All tests require a series of exercises under the adjustment test. The instructions of the test equipment manufacturers should be followed at all times. A record of the test result shall be generated and kept.

Qualitative adjustment test

The qualitative adjustment tests provide a pass or fail result depending on whether or not the user detects a test agent. The test agent can be detected by taste. They provide a subjective measure of the quality of sealing of the facial piece on the user's face. They are usually easy to perform and do not require specialized equipment or highly trained personnel.

This method introduces a controlled concentration of aerosol into a hood placed over the user's head. This test is suitable for disposable masks and half-masks. Please note that although half masks can be used with vapour and gas filters, their fit should only be tested with particulate filters. Some national authorities, for example in the United Kingdom (INDG479), do not allow the fit test of full face masks with higher protection factors using qualitative methods. See national regulations where they exist.

Benefits

• Cheap

• Easy to use

• No need to calibrate equipment

• No need to modify the face part

• Detection makes the user feel more involved in the test

Disadvantages

• Subjective testing: based on user response

• Full face masks cannot be tested

Quantitative adjustment test

Quantitative fit tests give an objective measure of the sealing quality between the wearer's face and the face piece. An adjustment factor number is calculated. These tests require specialized equipment.

Particle counting device in the environment

These devices usually rely on particles that naturally circulate through the ambient air. The test involves connecting a face piece with a probe, through a plastic tube, to the counting device. They count the particles of a certain size identified within the facial piece. This number is compared to the number of particles counted outside the mask in the ambient air. In certain cases, it may be necessary to increase the concentration of particulate matter in ambient air by means of a particulate matter generator. The result of this test is expressed as the ratio of the particle counts inside and outside the mask and is called the adjustment factor. These adjustment factors can often be high and should not be confused or used as a basis for selecting a mask.

Benefits

• Objective numerical result

• Objective result, independent of user perception

• Most have software to print the records

Disadvantages

• Expensive

• Know how to place the probe in the mask

• Training of the test operator is recommended

• Requires an additional adapter to test FFP1, FFP2 or P1 or P2 filter masks

Controlled negative pressure device

This test method uses a device to remove air from the facial piece and then maintain a constant negative pressure inside the facial piece while the user holds their breath and remains motionless. It measures the speed at which air needs to be extracted from the facial part to maintain negative pressure; it can only be used with facial parts with removable filters or air supply connections.

Benefits

• Does not require a specific concentration of environmental particles

• Does not require probe in mask

Disadvantages

• Disposable face masks cannot be fitted

• The user requires a good breathing technique

Adjustment factors

The minimum adjustment factors required are defined by national rules, if any. The following are the minimum adjustment factors as defined in UK INDG479 and ISO 16795-3. Check the local guidelines.

Minimum adjustment factors required for quantitative adjustment tests (taken from the INDG478 standard on adjustment testing of respiratory protective equipment (EPR). Health and Safety Executive (HSE) of the United Kingdom).

For the purpose of this Regulation, the following definitions shall apply:

Aid for the qualitative adjustment test 3M

3M provides two qualitative adjustment test kits: FT-10 (sweet) and FT-30 (bitter). In kit FT-10, a test solution of saccharin sodium is used to produce a sweet-tasting spray and in kit FT-30 denatonium benzoate (BitrexTM) is used to produce a very bitter taste. Each kit contains a hood and ring set, two nebulizers, sensitization solution, test solution and detailed instructions for use. The choice between the bitter and sweet test kit is personal, however, a small percentage of the population cannot detect the taste of saccharin, in which case the bitter test should be used. The test procedure involves placing the hood on the wearer of the PPE without the wearer putting on his mask. Using a nebulizer, an aerosol of the sensitivity solution is introduced into the hood to establish the user's ability to detect the solution. The sensitivity solution is a highly diluted version of the adjustment test solution. After a few minutes' rest, to allow the flavour of the sensitivity solution to dilute, the wearer puts on the mask and the hood back on. The test solution is now sprayed to the concentration level determined by the sensitivity test. This level is maintained throughout the test by introducing more solution at set intervals. The user then performs a series of exercises that include breathing, head movements and conversation. If the complete test is completed without the user detecting the spray, the test shall be deemed to be passed. If aerosol taste is detected at any time during the test, the test is terminated. After waiting at least 15 minutes for the aerosol to dilute, the test may be repeated. If repeated failures are experienced, an alternative mask size or model should be tested.

Aid for the quantitative adjustment test 3M

Disposable masks 3M and the maintenance-free reusable 3MTM medium mask, series 4000+ can be quantitatively tested with a portable counting device. This type of equipment includes adapters that perforate the mask filter material or mask body to allow the placement of a probe. Once equipped with a probe, test masks cannot be worn in the workplace.

If the range 3M for full or half face masks, a quantitative fit test is required, then the appropriate adapter should be chosen. This depends on the mask filter connection system and the quantitative adjustment test system used. For ambient particulate count quantitative adjustment tests, 3M offers different adapters, such as the 3MTM 601 quantitative fit test sampling adapter for masks with a bayonet filter connector 3M, or the 3MTM HF-800-03 Secure-ClickTM quantitative adjustment test adapter kit for masks with a Secure-Click filter connector.

Do you have any doubts regarding the respiratory adjustment tests?

We're here to help you. Contact our respiratory protection specialists, who are available to share their knowledge of the industry, regulations and products and help you select respiratory options that keep you and your workers protected.

It's from: 3M Spain, S.L.