An airborne contaminant is any type of material or gas that does not normally occur in the natural ambient atmosphere. Unlike other types of hazards in the workplace, airborne contaminants are often overlooked because of their small size and ubiquitous nature.
You may not be able to see, feel or even smell them; however, the lungs are an extremely efficient sponge and quickly absorb oxygen as well as contaminants from the air we breathe.
Preventing airborne contaminants from entering the workplace, prohibiting workers from entering such environments and providing adequate ventilation are the first steps that should be taken to protect workers from air borne hazards. Sometimes, however, this is not possible and Respiratory Protection Equipment (RPE) must be worn.
A critical aspect of the respiratory protection programme is selecting the correct type of respirator for the type of contaminant. Anyone who has ever performed physical work while wearing a respirator knows that respirators can be uncomfortable to wear, cumbersome to use, and interfere with communication. These issues make the selection process important. The goal must be to provide an acceptable level of protection without overly burdening workers. Balancing these factors is crucial to the effective protection of your workforce.
The purpose of this article is to review:
- • Airborne contaminants commonly encountered
- • Available respiratory protective equipment
- • Correct fit and use of air purifying mask respirator
- • Maintenance of your investment in equipment
Breathing hazards found in the work place
Alveoli are the tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide into and out of the blood takes place. Contaminates in the air we breathe can quickly enter our body via the alveoli and other parts of the respiratory system that lead from the lungs to the nose and mouth. The kinds of hazards which may require the use of respiratory protection include:
• Particulate contaminants
• Gas contaminants
• Oxygen deficiency
Particulate contaminants are solid or are solid or liquid particles suspended in the air. These particles can be in many forms such as biological (bacteria, mold, spores, fungi, virus), chemical (consult the MSDS for the compound), dusts, fibres, fumes or mists – see below. The natural filtering mechanisms in the nose usually capture particles in the 5 to 30 micron and larger sizes. Particles 1 to 5 microns in diameter can enter the windpipe and upper branches of the lungs. Particles with diameters less than 1 micron tend to enter the lower lungs. About 10% of these particles remain in the lung while 90% are exhaled. Whether particles that remain damage the body depends on what they are.
Dusts are solid particles which are suspended in the air. Dust is generally created by the cutting, grinding and crushing of solid materials. Silica dust generated when sand blasting is an example of a dust that is particularly harmful to the lungs due to its small size and physical structure.
Fumes are solid condensation particles that can range in size anywhere from 0.1 to 1000 microns. Fumes are commonly found in the air where soldering, welding and brazing work is conducted.
Mists are tiny liquid droplets given off whenever a liquid is sprayed, mixed or agitated. Spray painting is an example of where mists are formed.
Fibres are solid particles with an aspect ratio of greater than 3:1. Asbestos is a common type of fibre contaminant.
Gas contaminants are toxic gases and vapours which are present as molecules in the air. Their effects vary according to the composition of the gas. Gas contaminants quickly enter the blood system via the alveoli.
Toxicant is any gas that is capable of producing serious injury when entering the body in a sufficient concentration. Examples include hydrogen sulfide, chlorine, ammonia, sulphur dioxide, and hydrogen cyanide. At very low concentrations toxicants may only be irritants.
Carcinogens are any airborne compounds of materials that cause cancer. Examples include aromatic hydrocarbons, formaldehyde, nickel compounds, and cigarette smoke.
Vapours are formed by the evaporation of liquids. Solvents that are used in spray painting and paint cleaning such as acetone and toluene are contaminants.
Asphyxiants are chemicals that either displace oxygen (a simple asphyxiant) or restrict the body’s uptake of oxygen (a chemical asphyxiant). Nitrogen, hydrogen, helium, methane and halon are simple asphyxiants. Chemical asphyxiants include carbon monoxide, phosgene and cyanide.
Oxygen deficiency is a common workplace respiratory hazard. An atmosphere with oxygen content below 19.5% is harmful to the human body. Oxygen deficiency usually occurs in poorly ventilated areas such as confined spaces and typically involves an asphyxiant.
Respiratory Protective Equipment
Industrialised countries have regulations addressing respiratory protection requirements. In the US it is addressed by OSHA in 29 CFR 1910.134. The European Union utilises several standards, including: EN149 (disposable filtering face piece respirators), EN 405 and 140 (half masks), EN136 (full face masks), EN141 (gas/vapour combination filters), and EN143 (particulate filters). Australia and New Zealand use AS/NZS Standard 1715. Canada uses CSA Standard Z94.4-03. These standards provide a solid foundation for any respiratory protection programme. All of these require that employers select certified respirators that are appropriate for the concentration, chemical state and physical form of the contaminant.
The two main categories of respiratory protection are:
• Air purifying respirators
• Air supplying respirators, including powered air purifying respirators
A tool used by regulators and manufacturers that helps decide which type of RPE to use is the Assigned Protection Factor (APF). The APF of a respirator reflects the level of protection that a properly functioning respirator would be expected to provide to a population of properly fitted and trained users. Many air purifying respirators have APFs ranging from 10 to 50. Air supplying respirators and powered air purifying respirators have APFs ranging from 1,000 to 10,000. An APF of 10 is interpreted to mean that a user could expect to inhale no more than one tenth of the airborne contaminant present.
When used in conjunction with the Occupational Exposure Limit (OEL) provided in the MSDS a measure of filter appropriateness can be provided. For example, if the measured contamination level is 30 mg/m3 and the OEL is established as 5.0 mg/m3 then a respirator with a minimum APF of 6 is required. From a practical standpoint it’s wise to use a safety factor of at least 4 in calculating the APF. Using a mask with an APF of 24 would be wise due to the many uncertainties involved. If the calculated APF exceeds 50 then a supplied air or powered air purifying type of system should be considered due to the significantly greater APF.
Air purifying respirators provide protection by filtering the air supplied to the wearer. They work by drawing inhaled air through a filtering medium which reduces the contaminant level in the air before it is inhaled. These are?referred to as negative pressure respirators because the pressure inside the mask filter medium must be lower than ambient air pressure during inhalation. The advantages of air purifying respirators are:
• Simple to use
• Cause minimal restriction of movement
The disadvantages of air purifying respirators are they:
• Require knowledge of the contamination level
• Cannot be used in oxygen deficient atmospheres
• Do not remove 100% of the contaminant
• Restrict breathing and become clogged, making it increasingly difficult to breathe
Powered air purifying respirators (PAPR) rely on filters just like the negative pressure air purifying respirators but they are equipped with a battery powered blower to provide a positive pressure inside the mask. PAPR have similar safe use conditions (e.g. contaminant identity and concentration must be known, respirator does not supply oxygen) but are generally more comfortable for long term use and have significantly higher APF. What makes the PAPR different from the negative pressure respirators is the inclusion of the motorised blower, which pulls the air through the filter and blows it into the wearer’s breathing zone. This can produce a number of advantages over negative pressure respirators, depending on the application and workplace conditions.
Air supplying respirators provide protection by blocking ambient air and supplying stored air or oxygen to the wearer. The air or oxygen is supplied from a source different to the atmosphere the person is working in, such as a compressor, cylinder or air line.
Air supplying respirators are mainly used for:
• Oxygen deficient atmospheres
• Highly toxic atmospheres where air purifying cannot filter the contaminant amount below the acceptable exposure level
• Situations where full face and body protection is also required
This article only discusses the use of air purifying respirators since they are the most common found in the workplace.
Disposable mask respirators
Disposable mask respirators are the simplest of all air purifying respirators. They are sometimes referred to as non re-useable, single shift use, or maintenance-free masks – although some manufacturers offer re-useable models that can be cleaned and re-used for more than one shift. They are typically made of a synthetic form-molded filtering media which completely covers the nose, mouth and chin area of the face. The entire mask acts as a filter and traps contaminants as air is breathed in through the material. Some disposable masks have an exhalation valve. This feature helps to reduce humidity and heat, and reduces resistance when breathing out. In terms of the classification used by EN149:2001 some common uses offered by manufacturers are as follows:
• Class FFP1 protection against non-toxic solid and liquid aerosols in concentrations up to 4xAPF. These masks protect against mechanically generated particles from bagging, demolition, and sweeping. Mask removes up to 80% of 0.6µ airborne particles
• Class FFP2 protection against non-toxic and low to average toxicity solid and liquid aerosols in concentrations up to 10xAPF. Masks protect against mechanically and thermally generated particles such as machining, grinding, painting, woodworking, and brazing. Mask removes at least 94% of 0.6µ airborne particles
• Class FFP3 protection against non-toxic, low to average toxicity solid, and liquid aerosols such as metal fumes from welding, asbestos, virus, and bacteria in concentrations up to 20xAPF. Mask removes at least 99% of 0.6µ airborne particles
Be certain to read the manufacturer’s data sheet to fully understand the capabilities and limitations of any mask prior to use. Also, before donning a disposable respirator mask you should check:
• Mask for any physical damage such as holes in the filter material
• Edge seal to assure it conforms to the face
• Straps for adequate tension
• Metal nose clip for conformance to the shape of the nose
Mask fit requirements
General Everyday Fit Requirements
Prior to wearing a mask for work purposes regulations specify a medical check of the individual and a fit test of the mask to be used. These rigorous assessments have specific protocols for medical and HSE professionals to follow. Once the individual and the specific RPE equipment have been qualified the worker can proceed to don the equipment. When donning the disposable mask make sure that the lower and upper straps are in the correct position and the mask fits tightly against your face.
Test the seal around your nose and mouth by covering the filter mask with both hands and sharply inhaling. If there is a proper seal the respirator mask will collapse back onto your face. If there is not a proper seal you will feel an air stream channelling through the leak. Re-adjust the mask until a proper seal is achieved. Disposable mask respirators should be replaced as soon as there is any noticeable difficulty in breathing. Large amounts of dust and moisture can quickly clog the filter material. Unless specifically designed for such purposes, never attempt to extend the life of a disposable mask by water washing or back-flushing it with air as this will damage the filter material.
To provide adequate protection the mask must be worn at all times while exposed to the contaminant. If you have to remove or adjust the mask, first leave the contaminated atmosphere.
Replaceable cartridge filters
The more durable forms of respiratory protection devices utilise filter cartridges to purify the breathing air. These cartridges themselves are disposable but the mask they fit into is sturdy and re-useable. The cartridge fit must be robust and secure – a threaded mechanism is common. The benefit?of this system is that cartridges can be changed when they get clogged and to fit the hazards in the atmosphere. A wide range of cartridges are available.
Generally, a filter cartridge is designed to be effective in filtering one type or class of particle or gas. For this reason it is important to carefully review the manufacturer’s data and, if further information is required, discuss the expected work environment issues with the supplier.
EN141 is the EU standard for the classification of replaceable filter cartridges to remove specified gases and vapours or combined filters for removing solids and/or liquid particles and specified gases and vapours. The standard utilises lettering and colour codes to specify four types of gas component removed:
• Type A : certain organic gases and vapours with a boiling point higher than 65°C
• Type B: certain inorganic gases and vapours excluding e.g. carbon monoxide
• Type E: sulphur dioxide and other acidic gases and vapours
• Type K: ammonia and organic ammonia derivatives
EN141 allows other codes and colours to be specified by the manufacturer. It also uses a 1, 2, and 3 numbering convention to indicate absorption capacity for low, medium and high absorption capacity.
Combination particulate/gas filters are also available. These are used where there is both a particulate contaminant and a gas contaminant in the atmosphere.
Combination filters can either consist of:
• A gas filter with a particulate filter attached to it on the inlet side; or
• A composite filter media which removes concentrations of gas and certain particulates
EN143 addresses particle cartridge filters. These are classified according to their filtering efficiency. Here again there are three classes of filter P1, P2 and P3. P1 filters are intended for use against solid particles only; P2 and P3 are subdivided according to their ability to remove either solid and liquid particles, or only solid particles.
Like disposable masks, filter cartridges are affected by the concentration of the contaminant, humidity levels and the breathing rate of the wearer. The following checks should be conducted before using a half-face respirator mask:
• Dirt, cracks or tears on the face-piece
• Good seating of inhalation and exhalation valves
• Filter cartridges securely fitted
• Head-straps aren’t torn or broken
Re-useable half-face mask respirators
General Everyday Fit Requirements
Half-face mask respirators are similar in function to disposable mask respirators but have a more complex design that allows a better fit, less leakage, and higher filtering efficiency. The mask is made of rubber or a flexible synthetic material designed to cover the nose, mouth and chin area. The mask is commonly fitted with inhalation and exhalation valves. One or two replaceable filter cartridges are screwed into the mask in front of the inhalation valves. The type of cartridge selected will depend on the contaminant and concentration.
The head straps must be in the correct positions so the mask fits tightly against your face. Test the seal by covering both filter cartridges with your hands and sharply inhaling. If there is a proper seal the respirator mask will collapse back onto your face. If there is not a proper seal you will feel an air stream channelling through the leak. Re-adjust the mask and confirm the cartridges are properly screwed in until a proper seal is achieved. Test the seal again by covering the exhalation valves with your hands and gently exhaling. If there is a proper seal there should be a slight pressure build up inside the mask.
If there is not a proper seal you will feel an air stream channelling through the leak. Re-adjust the mask until a proper seal is achieved.
Both filter cartridges should be replaced at the same time whenever:
• Breathing becomes difficult
• Your nose or throat becomes irritated
• You detect any odour or taste
Half-face mask respirators rely on the facial seal to protect you from airborne contaminants. Facial hair such as beards or stubble prevents a proper seal from being maintained. Half-face masks should only be used by a person who is clean shaven. If you have to remove or adjust the mask, first exit the contaminated area.
Full-face respirator masks
Like half-face mask respirators these masks are also made from rubber or flexible synthetic materials but are fitted with a built-in clear plastic lens to cover the eyes, nose, mouth and chin. These usually have multiple adjustable straps to provide a flexible and secure fit to the wearer’s face. Full-face mask respirators are commonly fitted with a filter canister which is either connected directly to the face-piece or connected via a flexible tube. Canisters operate in the same way as cartridges but provide greater filtering efficiency because of the greater volume of absorbent material and internal design.
The full-face mask respirators are commonly used for protection against highly toxic dusts, gases and vapours, such as hydrogen cyanide gas, where protection is required to prevent contaminants being absorbed into the body through the eyes. The checking and fitting rules for half-face masks also apply to full-face masks. You must be clean shaven to get a secure seal on a full-face mask respirator.
Care and maintenance of respirators
Non-disposable masks require cleaning, disinfecting, storage, inspection, and repair. Each user should be provided with a respirator that is clean, sanitary, and in good working order. The manufacturer’s recommendations for care must be followed. Furthermore, the respirators should be cleaned and disinfected at the following intervals:
• Respirators issued for exclusive use should be cleaned and disinfected as often as necessary to be maintained in a sanitary condition
• Respirators issued to multiple users should be cleaned and disinfected before being worn by different individuals
• Respirators maintained for emergency use should be checked monthly and disinfected after each use
• Respirators used in fit testing and training should be disinfected after each use
All respirators should be stored to protect them from damage, contamination, dust, sunlight, extreme temperatures, excessive moisture, and damaging chemicals.
Make sure that you wear the correct respiratory protective equipment for the type of airborne contaminant that is present. Always check the respirator seal and valves because with any leak you are not protected. Wear your respirator at all times where a contaminant is present.
Change disposable respirator masks, filter cartridges and canisters as soon as you suspect they are becoming clogged or failing to filter out the contaminant. If in any doubt as to what respirator you should be using refer to Material Safety Data Sheets, your Supervisor, your Safety Adviser, the equipment supplier or the manufacturer.
You Probably Didn’t Know
• If the average person’s lungs were spread out flat on the ground they would have enough surface area to cover a tennis court!
• The normal air we breathe is made up of 79% simple asphyxiant gases.
Although every care had been taken in providing this information, the authors accept no responsibility or liability for any consequences arising from the use of such information.
Published: 10th Aug 2010 in Health and Safety Middle East