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During those halcyon pre-Covid days, for non-health and safety people, “PPE” (personal protective equipment) was something in the background, something people used at work and, maybe, when doing some DIY. Early in 2020 “PPE”, “face coverings” and “masks” became a focus of discussion in everyday-Covid-lives.
Confusingly, the terms “face coverings” and “masks” are interchangeable. We were told to wear them to prevent the spread of Covid-19. The aim was to stop virus-laden “droplets” (aerosols) escaping the noses and mouths of virus carriers and reaching others. That is, the face coverings were to protect other people from the wearer. However, many of us were familiar with the term “mask” as a term to describe personal respiratory protection, i.e. something that protects the wearer from an airborne contaminant.
The furore about initial shortages of “PPE” available for health care workers further confused matters. The PPE included personal respiratory protection to protect against infection from COVID patients, i.e. the “masks” the health care workers needed were personal respiratory protection not “face coverings”. Whilst there is some evidence that face coverings such as medical masks will prevent some virus-laden droplets reaching the wearer’s nose and mouth, the protection against small aerosols is very limited.
“selection of the right respiratory protection for any given contaminant is crucial”
In short, it’s not surprising that many people did, and some continue to, don a face covering with the aim of protecting themselves. Effective protection by PPE requires a good grasp of the principles that underpin its selection and use, and personal respiratory protective equipment (PRPE) is one of the more complex forms of PPE.
Key to protection of the wearer of PRPE is the ability it has to filter out the airborne contaminant (virus laden droplets, dust, gas, or vapour), and the seal it makes with the face such that no air can leak in; the contaminated air must only enter the wearer’s breathing zone through the filter.
To achieve the desired protection, there are several steps to take. The following steps comprise a PPE Programme.
Selection
Selection of the right respiratory protection for any given contaminant is crucial; a simple particulate filter is no use if the contaminant is a gas. Therefore, we start with an understanding of what we are protecting people against and how much of it is in the air.
The safety data sheet (SDS) for a substance provides much of the information needed to select the type of filter needed. Sometimes it will be apparent that there is more than one form of contaminant and a combination of filters is required.
The amount of the contaminant in the air is harder to address. It is very important because different types of respiratory protection offer different degrees of protection. However, in my experience, protection is very often selected on the basis of a guess at the amount of contaminant in the air.
Generally, disposable half masks (the filtering face piece (FFP) masks often described as ‘paper’ that cover the nose and mouth) offer relatively low protection; the reusable silicone rubber half masks with detachable filters offer higher protection; full face masks that seal around the perimeter of the face offer higher protection again; and powered masks that blow filtered air into the wearer’s mask generally offer the highest protection. Breathing apparatus and other air-supplied equipment, has higher levels of complexity and is dealt with separately to respirators.
“respirator users should undertake a simple qualitative face seal test every time they don a device”
Different items of respiratory protection are assigned a “protection factor”. This is the ratio of the amount of substance in the air outside the respirator to the amount of the substance that can be breathed by the wearer. For example, if a respirator has an assigned protection factor (APF) of 10, the amount of a contaminant the wearer might inhale will be one tenth or less of the amount in the air.
Nevertheless, to select a respirator that will reduce the air contaminant to an acceptable level, knowledge of the airborne concentration is required and this will generally require air sampling.
Whether a wearer achieves the expected protection will depend on several things including the correct fitting of the respirator, its condition (maintenance) and its use for the entire time that there is potential exposure.
Achieving the correct fit can be difficult and so respirator users will generally undergo “face fit testing”. This involves the wearer being instructed in fitting and then being subjected to exposure to an innocuous substance, such as a saccharine mist. If saccharine can be tasted, there is not a good seal between the respirator and the face and adjustment is required. Sometimes a face seal cannot be achieved, and an alternative type of respirator has to be used.
Most employers will have to engage a third-party training provider to undertake face fit testing and train PRPE users. Interestingly, not only was training made difficult by the infection risks during the early stages of the Covid-19 pandemic, but also there was a shortage of face fit (saccharine) testing kits owing to the sudden increase in the demand, in particular, for testing health workers.
Generally, the APF should be considered the maximum achievable. The APF is determined by the manufacturer under ideal conditions. In the workplace, respirators are often fitted hurriedly and may not be “as-new”. The wearer may have facial hair that will prevent a good face seal. Ideally, respirator users should undertake a simple qualitative face seal test every time they don a device. This can be through blocking of the filter inlets with pieces of card or the hands and then inhaling; no air should leak in and the respirator should collapse on to the face. Disposable respirators (FFPs) are harder to test this way although cupping both hands over the entire facepiece and inhaling can give a good sense of a seal.
If a face seal cannot be achieved, a powered respirator may be required. This will have a battery powered fan that draws in air through a filter and blows it into the wearer’s facepiece. The facepiece may be a full-face mask or a hood. Sometimes the facepiece is integrated with a helmet and visor. Because air is blown in, the facepiece is under positive pressure. This means that any leakage will be outwards. Other respirators that rely on a face seal are under negative pressure. This means that, when the wearer breathes in, a partial vacuum is created inside the facepiece such that air is drawn through the filter. Any leakage is therefore inwards and the APF is generally lower than a positive pressure device.
A face seal cannot be achieved with face coverings such as medical masks, the wearer would fail a face fit test. These are not assigned a protection factor. However, those used in medical settings are usually required to comply with a certain standard (in the UK the standard is BS EN 14683:2019 Medical face masks – Requirements and test methods) that addresses factors such as splash resistance. The introduction to BS EN 14683:2019 says that the main intended use of medical face masks is to protect the patient from infective agents (for example from the noses and mouths of the staff). Medical face masks may also be worn by patients to reduce the risk of spread of infections from them. The standard acknowledges that in certain circumstances a surgical mask will protect the wearer against splashes of potentially contaminated liquids. Importantly it refers to splashes and not respirable aerosols.
“verifying the authenticity of certification at the time of selection is important”
PRPE must also meet standards. For example, in the UK, filtering half masks to protect against particles must meet BS EN 149:2001+A1:2009 Respiratory protective devices – Requirements, testing, marking. This standard requires specific markings on the facepieces and the packaging, a head harness, filter efficiency, etc.
Within Europe a declaration of conformance with required standards is needed. This is demonstrated through a “CE” mark on packaging and individual respirators (in the UK the CE mark is being replaced by a UKCA mark). The mark indicates that the respirator model has been independently tested and meets the requirements of relevant standards.
During the Covid-19 pandemic I assisted some purchasers of large volumes of PRPE that carried CE marks that had been fraudulently applied by the manufacturer. The masks may have been suitable as face coverings but did not meet the stringent requirements of the relevant standards for PRPE and were unlikely to provide the level of respiratory protection required and expected by the purchasers and required by the wearers.
I also assisted with a number of issues around masks claiming to be of “KN95 standards”. Very large numbers of these were imported to meet pandemic needs but many of the mask types did not provide adequate protection. KN95 is a performance level under a Chinese standard that is broadly the same as BS EN 149:2001. However, there is no independent certification or assurance of the quality of products manufactured to KN95 and they are declared as compliant by the manufacturer.
As such, verifying the authenticity of certification and the source of respiratory protection at the time of selection is important.
Apart from these various considerations, selection of the most suitable respiratory protection must take account of the work and tasks that are to be undertaken. It may not be practical to wear PRPE, a respirator may not be compatible with other PPE, it may be unreasonable to expect a respirator to be worn for the length of time a task takes, and some people may be unable to wear a respirator for medical reasons or for reasons of religious belief.
To improve the chances of a respirator being used properly, the users should be consulted. Discussions about the work, the substances used and the suitability of the proposed PRPE will often lead to better adoption. Sometimes it is of value to have trials of PPE and this may identify a need for different types for different tasks and different wearers.
Use
Having selected PRPE, it is important that it is used and used properly.
A respirator must be fitted before work commences in an environment with contaminated air and it should not be removed until the work is complete and the contaminant(s) is no longer present. “Percentage Time Worn” is sometimes used to assess PPE usage. 100% time worn is desirable, although comfort issues, breathing resistance and communication difficulties may lead to periodic removal. Whilst this is often perceived as short-term and of low consequence, those periods result in unprotected exposure. Also, proper replacement with a check of the face seal is unlikely every time the device is put back on.
Maintaining clean-shaven faces as were required during face fit testing is often difficult and the face seal obtained in everyday respirator use is usually inferior. Talking to respirator users about such matters and refreshing knowledge about achieving a good face seal will improve protection.
Storage and maintenance
Having a clean respirator in good condition is important to personal hygiene and respirator effectiveness. Obviously disposable respirators such as FFP masks negate the maintenance issues although they should be disposed of after each use. I regularly see FFP respirators being re-used.
Maintenance of re-usable respirators can be complicated and training of the user is required unless a dedicated maintenance service is provided. A relatively simple orinasal half mask might have an inlet (non-return) valve behind each filter cartridge, one or two exhalation valves with covers, the head straps, and facepiece itself. Full-face masks are further complicated as are powered devices. I have seen masks in use with valves not seating correctly and, in one case, the valve was missing after the respirator was serviced. Air will take the path of least resistance and thereby be drawn in through an open valve rather than the filter.
“a clean respirator in good condition is important to personal hygiene and respirator effectiveness”
I often see half masks that have not been cleaned or otherwise maintained. It is less likely that such masks will be worn.
Clean storage facilities are important. It is common to see respirators lying on work benches conveniently ready for the next use but accumulating dirt.
I have seen many instances of vapour cartridge respirators stored in the same locker as part-used paint cans or other chemicals. The vapour cartridges contain activated charcoal that collects (adsorbs) the organic vapours when contaminated air is drawn through. The charcoal will also passively adsorb vapours. This means that, whilst lying in the locker, vapours are still being adsorbed and the charcoal progressively becomes saturated.
Respirator cartridges do not have indicators to guide the user on their level of saturation. Some manufacturers provide the user guidance that, when the contaminant can be smelled or tasted, the cartridge is saturated and should be changed. Passage of the contaminant through the filter into the facepiece is referred to as breakthrough. At this stage the wearer is exposed to the contaminant. The aim should be to determine the maximum duration of use before the cartridges should be changed. This is difficult unless the likely airborne concentrations of the contaminant have been measured and can then only be an estimate of life span.
Particulate filters can become clogged and thereby breathing resistance increases and makes removal of the respirator more likely.
Training and education
Underpinning effective face fit, proper use, and maintenance, are education and training; educating about the hazards of the substances being worked with, the importance of always checking the face seal, maximising the percentage time worn and properly maintaining and storing equipment; and training in the practical skills necessary to fit, use and maintain equipment.
Research from 19991 found that of 211 half mask wearers taken from the workplace and tested, 69% failed a face fit test. It was found that the face fit test pass rate was significantly higher among wearers who were given structured training.
Respiratory protective equipment is often seen as quick and low-cost solution to a problem, but an effective personal respiratory protection programme requires a lot of work, it takes time, and the equipment and consumables are expensive. Therefore, any decision to use PRPE should start with consideration of the preferred options; can the airborne contaminants be eliminated through a change in process or through substitution by a safer alternative? Can enclosure or exhaust ventilation be used to reduce airborne concentrations? These may be more cost-effective solutions.
Respiratory protection remains, however, an important control measure. It may be necessary for a short-term risk control whilst a better control is developed. It may be necessary for maintenance tasks that cannot otherwise be controlled and occasionally it may be used as a supplementary risk control. Whatever the circumstances, it is a risk control measure that is very heavily dependent on procedures and the behaviour of individual PPE users, and it is therefore a low-reliability solution.
The lessons learned during the COVID-19 pandemic underline the importance of an understanding of the role of PPE in risk control and of carefully and cautiously selecting devices. Simply allowing the release of an airborne contaminant and preventing inhalation by covering the nose and mouth of everyone who might be exposed does not make sense when preventing or controlling release at source will mean that everyone is protected.
References
1 Burgess, G.L. & Mashingaidze, M.T. (1999) Respirator Leakage in the Pharmaceutical Industry of Northwest England, Ann. occup. Hyg., 43 8, 513-517
