Sizing up the market

Interest in respiratory protection has grown rapidly in recent years. Due to the pandemic, respiratory protective equipment (RPE) and airborne particles have become common topics of discussion. Google Trends data shows that searches for ‘respirator’ began to rise sharply in 2020, spiking in March at a 1900% increase, and are only now returning to pre-pandemic levels¹. The News on the Web Corpus reveals the same term appeared in news articles 4240 times during 2020, 1132 in 2021, and appears to be rising again at 1065 in mid-June 2022, compared to averaging only 143 appearances per year for the previous 10-year period².

Despite a marked increase in general awareness, fundamental misunderstandings remain when it comes to selecting and using appropriate RPE. The usual confusions surrounding choice of filter and how to wear a respirator correctly are compounded by inappropriate use of medical masks and the introduction of unstandardised face coverings. The appearance of KN95 masks on the European market and misuse of medical PPE in construction and industry applications has prompted safety alerts from the Health and Safety Executive (HSE) to clarify the appropriate uses for each product. 

Tight-fitting RPE

Without an understanding of how tight-fitting RPE works and the way air behaves, it could be assumed that any mask acts as a barrier to filter the worst of a hazard but, in fact, a mask needs to fit tightly to provide filtration. Air is fluid, being mostly made up of gases, and takes the path of least resistance. When a wearer inhales in a poorly fitted mask, it is easier for air to enter via small gaps in the face seal than to be drawn through the filter media.

Disposable dust masks (FFP masks), half masks and full face masks are classed as tight-fitting RPE. These respirators rely on creating a tight seal between the mask body and the wearer’s face to filter inhaled air. A well-fitted facepiece does not allow inhalation around the face seal, meaning air can only be drawn through the filters, ensuring the intended level of protection is provided. 

Is size important?

There is no ‘one size fits all’ approach when it comes to RPE. Each person’s face is a slightly different shape and size, and the mask must properly fit a wearer’s facial features to achieve an effective seal. Respirators are available in a range of sizes to fit different facial dimensions. Trying multiple masks in various sizes can help to find a suitable option. 

For over 50 years, the only available anthropometric information for respirator sizing was comprised of measurements taken in the US military during the 1950s and 1960s. The facial dimension data was used to select suitable participants for respirator testing. Recognising the existing data as not sufficiently representative of modern RPE users, Zhuang and Bradtmiller conducted a large anthropometric survey³, collecting data for 18 facial dimensions plus height and weight, from a sample of 3997 subjects covering a range of demographics.

The 2007 study resulted in the designation of five headform sizes which are detailed in international standard ISO 16976-2, Respiratory protective devices – Human factors – Part 2: Anthropometrics. The designated headforms are Small (S), Medium (M), Large (L), Short/Wide (S/W) and Long/Narrow (L/N). The S, M, L headforms are varying sizes with similar facial dimensions; the S/W and L/N headforms are based on different dimensions. The new data provides an improved way to select representative test panels for independent respirator assessment and certification. RPE manufacturers can use the designated headforms to design and produce respirators that offer an effective fit for a wider range of users. 

Fit testing

Tight-fitting RPE must be face fit tested to ensure the wearer can achieve a good seal with the mask. Fit testing must be carried out on initial selection of a respirator and repeated regularly thereafter. No worker should be wearing a respirator that they have not been fit tested with. Guidance recommends repeat testing every two years, though it may be more appropriate to conduct testing yearly. 

Face fit testing assesses the fit of a specific model and size of respirator on a particular wearer. The test subject dons the mask and completes a series of exercises intended to challenge the face seal. Qualitative testing is a subjective method using taste to identify leaks around the seal, applicable to disposable masks and half masks. Quantitative testing uses objective methods and reports a numerical result, showing how well the mask fits the wearer. Various quantitative testing methods can be used for disposable masks, half masks and full face masks. 

Once fit testing is passed, it is crucial to make sure the same model and size is worn for work. The mask must be fitted correctly, as in the fit test. Reputable fit test providers offer training on pre-use checks and inspections to be carried out each time the RPE is used. 

Keep checking

Every time the respirator is worn a ‘fit check’ must be performed. This is different to a fit test, a much briefer exercise, to make sure the mask has been donned and adjusted correctly. Fit check methods vary by respirator type but always involve blocking the filters to check inward leakage around the seal. This brief check ensures that the facepiece is fitted correctly before the wearer enters the hazard area.

Facial hair and stubble can compromise the effectiveness of tight-fitting RPE fit by creating gaps around the face seal. Though human hair is fine, it is relatively large compared to the size of a fine dust particle, and therefore capable of causing a leak through which hazardous particles can be inhaled. 

Compatibility with other equipment is another important consideration. When a respirator needs to be worn with additional PPE, the items must be compatible to avoid compromising protection. For fit testing, the test subject is kitted out in all the PPE and any other items worn around the face, head and neck areas during work. This includes prescription glasses and safety spectacles, goggles, faceshields, ear defenders, and any other equipment that may affect how the mask fits. Using compatible products and integrated PPE ensures respiratory protection is not compromised by other items, and that the performance of additional protective equipment is not affected by the respirator fit. 

Even a top-of-the-range respirator with ultra-high efficiency filters is no use unless it fits correctly. Selecting an appropriate size and getting fit tested is crucial to make sure the RPE is able to do its job. Wearers of tight-fitting respirators are required to be clean-shaven around the face seal and must complete a fit check each time the mask is worn. When other equipment is required to be worn with the mask, it must be compatible. Sampling methods resulting from the latest anthropometric survey enable test laboratories to select representative panels of subjects for performance assessment. The data provides manufacturers with dimension and size information to optimise RPE design, offering an effective fit for more wearers. By expanding the range of size options available and using more representative sample groups in respirator testing, the market is advancing to provide protection for the diverse population of modern RPE users. 

References

Louise Charlton is technical copywriter at JSP. For more information, visit www.jspsafety.com