Casella Measurement is a leading manufacturer of a complete range of workplace and ambient monitoring equipment, including dust, air, noise and heat. Gary Noakes, product manager, takes a look at the development of respiratory protective equipment and the importance of measuring and monitoring exposure to reduce potential hazards in the workplace.

Modern respiratory protection represents 200 years of development. It has been tested by war, tempered by fire, and trialled in the harshest working conditions imaginable. It will filter dust, neutralise poisons, capture bacteria and feed fresh air to keep the wearer alive and safe – but only under one condition. The mask has to fit.

All is for nothing if contaminants can outflank your defences and leak into the mask, and the main cause of leakage is a poor seal between the mask and the face. As a result of field and laboratory studies into respiratory performance, regulations and guidance across Europe now recommend that fit testing be an integral part of any respiratory protection equipment (RPE) programme for mask based devices.

RPE is capable of providing effective protection only if it is correctly selected, used and maintained. Unsuitable, poorly maintained and incorrectly used RPE may give limited protection or no protection at all. This could lead to ill heath in the short or long term, but if the RPE is being used in conditions where there is an immediate danger to life and health, it could prove fatal. As with all personal protection equipment, RPE is the last defence. If workers are exposed to airborne hazardous substances, respiratory protection equipment should be used only when the hierarchy of control measures such as monitoring, enclosure and ventilation, have been residual risk.

Relevant regulations

In the UK the Health and Safety Executive (HSE) is committed to reducing work related respiratory illness, and its latest move was the introduction of Workplace Exposure Limits (WEL), brought into force by amendments to the Control of Substances Hazardous to Health (COSHH) Regulations in early 2005. Most substances including gases and vapours have now been assigned exposure limits for short and long time frames, and are listed in the HSE publication EH40. For example, exposure to hydrogen chloride as a gas or aerosol mist at one part per million is permitted for eight hours, but only for 15 minutes if at 5 part per million.

COSHH regulations cover exposure to biological agents as well as chemical hazards, but unlike the industrial chemicals which have each been assigned a workplace exposure level there are no specific safe exposure levels for biological agents. The number of organisms required to establish different infections varies, and the general requirement is to reduce exposures to as low as reasonably practicable. The HSE recommends that where there is a respiratory risk of infection the use of FFP3 devices represents best practice, and where these are not available then FFP2 may be an acceptable, pragmatic compromise.

The approved codes of practice (ACoPs) supporting the Control of Substances Hazardous to Health Regulations 2002 (COSHH), the Control of Lead at Work Regulations 2002 (CLAW), the Control of Asbestos at Work Regulations 2002 (CAW) and the Ionising Radiation Regulations 1999 require that all reasonable steps be taken to prevent exposure to substances hazardous to health.

The regulations assert that ‘every employer shall ensure that the exposure of his employees to substances hazardous to health is either prevented or, where this is not reasonably practicable, adequately controlled’.

The hierarchy of principals for the control of exposure to airborne hazardous substances includes elimination, substitution, physical separation, and finally the use of personal protection equipment. There should also be a rigorous ongoing measurement and monitoring regime adopted in order to evaluate an individuals exposure to airborne hazards, adopt adequate control techniques and ensure their efficacy on a regular basis. Samples can be made with traditional personal air sampling pumps such as Casella’s TUFF together with sampling media, or by undertaking local area dust surveys with real -time direct reading instruments (DRI’s) such as the Microdust Pro again from Casella.

DRI’s will allow quick assessments of the workplace and individual tasks for inhalation hazards enabling you to make instant decisions, rather than waiting days for retrospective gravimetric data gained from traditional personal air samplers.

Monitoring and control methods

If after undertaking monitoring, and implementing control methods, the exposure levels cannot be adequately reduced, then RPE may have to be considered as the mainstay of the control regime.

Once committed to RPE, the buyer enters a confusing world of workplace exposure limits (WEL), assigned protection factors (APF), European Standards and legislative stipulations. What is clear is the fact that there are 17,000 new cases of occupational asthma each year in the UK, and there would be 4,000 fewer deaths from chronic obstructive pulmonary disease if occupational dusts, smoke and fumes were removed from the working environment.

Suitable RPE must be provided if exposure cannot be controlled another way, and to ensure that adequate protection is provided for individual wearers, the codes recommend fit testing of equipment.

In the US, where fit testing is a legal requirement, methods and protocols that must be followed are specified in ANSI and OSHA standards.

However, in the UK no particular fit testing methods and protocols are mandated. Whilst the HSE guidance document plays a vital role in educating both fit testers and RPE users in promoting good practice and in setting a benchmark, following this guidance is not compulsory. Pressure to reduce workers’ downtime has on occasions led fit tester to cut corners. Conducting a correct fit test requires competence, diligence and time. A badly conducted fit test can result in poorly fitting face-pieces being used, leading to wearer exposure.

Fit testing of tight fitting respiratory protective face-pieces has been in use for some years, and one test measures total inward leakage (TIL) into the mask which may include face seal leakage, filter penetration and exhalation valve leakage. For devices with high efficiency filters or a clean air supply, the greatest contributing factor is face seal leakage, defined as the inward leakage of ambient atmosphere between the face and the face-piece.

Total inward leakage of new designs is determined in the laboratory, but when the equipment is used at work a new variable is introduced – the infinite variety in size and shape of the human face. The levels of protection established by RPE during laboratory testing is never achieved in the workplace, and so the assigned protection factor (APF) was devised to provide a realistic measure of the protection likely to be achieved in the workplace by 95 per cent of adequately trained and supervised wearers using properly functioning and fitting equipment.

Filtering face-piece (FFP) respirators are classified as FFP1, FFP2 and FFP3 according to the level of protection afforded as assessed by laboratory tests, with FFP3 offering the most protection. The APF is the ratio of pollutant outside the device to that inside the device, and for FFP respirators of standard 1,2 and 3 categories these ratios are 4, 10 and 20 respectively, with 20:1 being the highest protection factor as found in FFP3 respirators such as the UVEX silv-Air FFP3 Respirator.

The fit of a face-piece can be determined by qualitative or quantitative methods. Qualitative methods rely on the wearer’s subjective response to a test agent, usually a sprayed solution of a sweet or bitter tasting substance. These tests are simple to perform and suitable for half masks and filtering face-pieces.

Quantitative methods require specialised equipment such as test chambers, particle counting devices and controlled negative pressure devices. They provide an objective measure of the fit, generating a number referred to as a fit factor, which relates to a specific face-piece/ wearer combination. This is different to the assigned protection factor, which relates to the performance of the whole device rather than just the face seal, and gives the likely performance of equipment when worn and used correctly; when specifying RPE for use at work the APF is used.

The method of face fit testing is a matter of striking the right balance between a fit test method that is scientifically sound but often not very practical, and a method that is easy to use whilst providing an acceptable assessment of fit. What is important is that the fit tester is aware of the limitations of a particular method, and takes these into account.

The best time to conduct fit testing is at the initial selection stage, when individual users should be given a choice of adequate models of RPE. Testing should also be carried out if the wearer loses or gains weight or undergoes any changes that may affect the fit. The performance of tight fitting face-pieces depends on achieving a good contact between the wearer’s skin and the face seal. As people come in all shapes and sizes it is unlikely that one particular type or size of PPE face-piece will fit everyone, and inadequate fit will significantly reduce the protection provided.

Where face-pieces are issued on an individual basis it is recommended that the wearer is fit tested using their ‘own’ face-piece. Where this is not practicable or pooled equipment is used then a test face-piece that exactly matches the wearer’s ‘own’ face-piece should be used. A competent person who should have received adequate instruction and training in fit testing should conduct the testing, and manufacturers of fit testing equipment often offer suitable training, and records of such training should be retained.

Prior to qualitative fit testing methods, the wearer should not eat, drink, smoke or chew gum for at least 15 minutes prior to the test. In the bitter/sweet tasting aerosol fit test method, the taste or smell threshold of the wearer must be established before the test to ensure the wearer can detect the odour being used in order for the test to work. The person is fit tested while wearing the respirator inside a hood, and the test solution (either bitter or sweet) is sprayed into the hood. If the wearer detects the taste of the aerosol during the test then the fit is unsatisfactory and the fit test is failed. This test can be used for filtering face-pieces FFP1, FFP2 and FFP3.

In the odour test method, the person is fit tested while wearing the respirator inside an enclosure, which contains a known concentration of isoamyl acetate (also known as banana oil). If the wearer detects the smell of the isoamyl acetate during the test then the fit is unsatisfactory and the fit test is failed. During both fit-testing methods the wearer will carry out a number of specified exercises such as deep breathing and head turning to challenge the fit of the mask.

Quantitative testing determines that a tight fitting face-piece provides an adequate seal to the wearer’s face by measuring microscopic particles that exist in ambient air; it measures the particles outside the face-piece and then measures the concentration of those particles that leak into the respirator whilst the wearer carries out a number of specific exercises. The three main types of quantative testing including the test chamber, the portable particile counting device and the controlled negative pressure device. The test chamber method is usually conducted in a laboratory due to the nature of the equipment involved. The wearer is fitted with a probed respirator and exercises on a treadmill within a test chamber into which a test agent of sodium chloride aerosol or sulphur hexafluoride gas is introduced. Through a comparative measurement of the level within the face-piece to that in the test chamber the face seal leakage can be derived.

The portable particle-counting devices usually depend on naturally occurring particles circulating within ambient air, and the test involves connecting a probed face-piece, via plastic tubing, to the counting device. Particles of a certain size identified within the face-piece are counted, and the number is compared with the number of particles counted outside the respirator in the ambient air. In certain cases, it may be necessary to increase the ambient air particle concentration by means of a particle generator. This test method is suitable for disposable respirators, half facemasks and full-face masks.

The controlled negative pressure device removes air from the facepiece then maintains a constant negative pressure within it while the wearer holds his breath and remains motionless. The rate at which air needs to be drawn from the facepiece to maintain the negative pressure is measured to give the rate of leakage into the face-piece. This method can only be used with facepieces with detachable filters or supplied air connectors.

Protecting workers

The issue of protecting healthcare workers against infectious respiratory viruses was highlighted following outbreaks of Severe Acute Respiratory Syndrome (SARS) in the Far East and Canada in 2002-2003. Significant numbers of healthcare workers were infected with the virus, which is thought to be spread primarily via large droplets and direct contact. Studies on the clinical infection rates during the management of outbreaks in hospital settings suggested that surgical masks afforded some protection, but this was not enough to significantly reduce the risk of infection. The studies also suggested that better RPE may be necessary to protect healthcare workers from SARS and the more recent strains of influenza.

Respiratory protection equipment for the military, for the emergency services and for industrial, scientific and medical workers has saved millions of lives over two centuries. The development of standards and protocols such as precision face fit testing, assigned protection factors and workplace exposure limits over many decades has turned the development of masks and respirators into a science, and the job of specifying and using them effectively into an art.

The long history of respiratory protection hasn’t always been so scientific, and primitive attempts to defend workers from smoke and dust have been documented for hundreds of years. Leonardo da Vinci (1452- 1519) worked on a system of protecting against smoke and chemicals, and in 19th century America the search for protection centred upon the fire services. Stories abound of early fire departments, which required men to wear full beards in order that the hair could be wetted and clamped in their teeth as a means of keeping larger airborne particles from entering their airways.

In 1823, the English brothers, John and Charles Deane patented a smoke protecting apparatus for firemen that was later modified for underwater divers. At around that time that the German born, British engineer, Augustus Siebe was marketing an early diving suit based on the Deane concept that included a helmet into which air was pumped via a tube, with spent air released through a valve. The inventor founded the company Siebe, Gorman and Co, which developed and manufactured respirators for a variety of purposes and was later instrumental in developing military gas masks.

Among the early forerunners of the gas mask was a device invented in 1847 by American Lewis P. Haslett. The device allowed the wearer to breathe through a nose or mouth piece fitted with two one-way clapper valves, one to permit the inhalation of air through a bulbshaped filter and the other to vent exhaled air directly into the atmosphere. Similar use of valves became common in later masks, and is a feature of most modern respiratory protection equipment. The filter material – wool or other porous substances moistened with water – was sufficient to keep out dust and other solid particulates, but would not have been effective against poison gas. In 1849, Haslett’s Lung Protector was granted the first US patent for an air-purifying respirator.

The necessities of war speeded the development of respirators, and the first mass chemical gas attack in April 1915 by the Germans caught the Allied forces by surprise. Soldiers tried to breathe through cotton pads socked in urine and others used socks or handkerchiefs soaked in bicarbonate of soda. It was not until July of that year that soldiers were given gas masks and anti-asphyxiation respirators to protect them against the chlorine, phosgene and later the odourless mustard gas used by both sides for the remainder of the war.

Canadian, Cluny Macpherson designed a fabric ‘smoke helmet’ with a single inhaling tube impregnated with chemical sorbents to defeat the airborne chlorine used in the gas attacks and provide some facial protection from the skin blistering chemical agents. However, the most widely used gas mask was the British Small Box Respirator (SBR) designed in 1916 and used by British troops for the remainder of the war. The SBR filtered dangerous gasses through a canister of charcoal, and gauze impregnated with neutralising chemicals, and a canvas covered rubber hose attached the mask of thinly rubberised canvas to the canister.

Even before Europe descended into this conflagration the American Congress established the United States Bureau of Mines (USBOM) in 1910, after a decade in which coal mine fatalities exceeded 2,000 annually. The bureau was to work with mining companies to develop safety procedures and technology to reduce accidents in the coal mining industry, but its progress was not sufficient to prevent the death of 470 workers who died of exposure to silica dust during the construction of a tunnel in Gauley Bridge.

It was one of America’s greatest industrial disasters, and a further 1,500 workers were disabled by silicosis. The tragedy led to Congressional hearings, the findings of which spurred calls for greater safety at work and several decades of vigorous health and safety lawmaking.

Today, while America and Europe lead the world in respiratory protection legislation and technology, some developing countries still don’t have standards for the use and performance of respiratory protection. However this is changing as a result of the growing awareness of occupational health and safety issues amongst workers and governments, and the International Standards Organisation (ISO) currently is developing global respirator performance standards that will be available for all countries to incorporate into health and safety regulation.

Respiratory protection now exists to challenge the 40 conditions that affect the lungs and airways, ranging from asthma to lung cancer. Some conditions such as mesothelioma can take 60 years to develop, and while little can be done for the 3,000 people who die in the UK each year as a result of exposures to asbestos back in the 1960s, it is time to consign tragedies like that to the industrial dark ages. By undertaking regular and appropriate personal and area exposure monitoring, specific control technologies can be adopted. If the substances cannot be excluded from the process, or adequate control cannot be achieved by other engineering methodologies, then RPE will offer the rear guard in protection for the workforce.

Author Details:

Gary Noakes, Product Manager Casella Measurement

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Published: 10th Nov 2009 in Health and Safety International