Air-purifying respirators

THE AIR YOU BREATHE

Few types of personal protective equipment are more complex -- or more critical -- than breathing protection. Here’s what you need to know about air-purifying respirators.

By Hayley Chandler

Many jobs and tasks, from spray painting to working in confined spaces, expose the workers to hazardous substances in the air. In order to have clean air to breathe, workers will require some form of respiratory protection.

While there are a great many types of equipment available to deal with a wide variety of contaminants, all breathing protection falls into one of two categories. First, there are "supplied air respirators", which, as the name suggests, provide a supply of clean, safe air to the wearer. These may be "air-line" respirators -- which pump air along a hose to the wearer’s face mask -- or "self-contained breathing apparatus" which use backpack tanks similar to those used by divers. Second, there are "air-purifying respirators" which use filters of various kinds to remove contaminants from the air in the workplace. (Dust masks -- small, disposable paper filters that fit over the mouth and nose by means of a singe elastic band -- are designed to remove nuisance substances such as dust only; they are not considered respirators.)

Air-purifying respirators remove contaminants from the air by passing it through a cleansing medium, such as a filter, a cartridge or a combination of both. The filter or cartridge traps the contaminants, removing them from the air before it is inhaled into the worker’s respiratory system.

There are many different types of air-purifying respirators. "You have to make sure you understand the hazard you’re dealing with and the form that it comes in -- dust, mist, fume, gas or vapour -- in order to make the appropriate selection," says Jeff Narver, market supervisor, for occupational health and environmental safety at 3M Canada Company in London, Ontario. Air-purifying respirators can be categorized based on the form of contaminant they provide protection from: particulates, vapours or gases.

Particulate removing respirators use a filtration method to remove a single type of particulate matter (such as dust) or a combination of two or more types (such as dust, mist, fume or smoke) from the air. The filtration method is either simple straining, which occurs when the particle size is larger than the size of pore in the filter, or a multi-layer filtration process, which uses a number of different mechanisms to capture fine particulate matter.

Particulate-removing respirators are available in the following configurations:

* A simple filtering-facepiece respirator uses the filtering material to form a mask, which fits over the worker’s nose and mouth. This type has two straps to ensure a proper fit, which may or may not be adjustable. Some have a nose clip, which helps to customize the fit. Other models have exhalation valves, which make breathing easier and reduce heat and moisture buildup inside the facepiece. They have no replaceable parts and must be disposed of once the filter becomes clogged.

* An elastomeric-facepiece design has a molded facepiece that fits over the nose, mouth and chin (called a half facepiece) or over the nose, mouth and eyes (called a full facepiece). A full facepiece respirator protects the eyes from particles in addition to providing respiratory protection. A quarter facepiece design, which fits over the nose and mouth but does not cover the chin, is sometimes available but "they’re almost non-existent in the industry," says Narver. All elastomeric facepieces have one or two attachments that hold filters. They also feature inhalation and exhalation valves.

Vapour- and gas-removing respirators are equipped with chemical-absorbing cartridges to remove a single vapour or gas, a single class of vapours or gases (such as organic vapours), or a combination of two or more classes of vapours and gases from the air. They feature molded, elastomeric-facepieces in full- and half-facepiece configurations. Vapour- and gas-removing respirators are also available in the form of a mouthpiece respirator or "bite block" that is used only for escape purposes in the event of a contaminant leak or a spill. It is simply a cartridge with a mouthpiece similar to the mouthpiece on a snorkel and a nose clamp to prevent breathing through the nose.

"It’s very common to have multiple hazards in a workplace," says Narver. For example, if you’re spray painting, your prime hazard would be a vapour but you’re also creating a mist, which is a particulate. So in order to protect your lungs, you need a filter and a chemical cartridge. This is where combination particulate-, gas- and vapour-removing respirators come in. They are equipped with both filters and cartridges to remove particulate matter, vapours, and gases from the air. The filter and cartridge can be permanent or replaceable parts.

It is also possible to purchase powered air-purifying respirators, which contain a blower, either stationary or carried by the wearer, that passes ambient air through a cartridge, filter or combination of both, and then supplies purified air to the facepiece or mouthpiece and nose clamp. Powered types are equipped with a facepiece, helmet, hood or suit. They can be used for particulates, gases and vapours or a combination of both forms of contaminants.

Determining the form of contaminants in your workplace is only one step in the selection process. Many other factors must be taken into account. And, in addition to determining the type of respirator you need, you must also select the appropriate type of cartridge or filter for the particular conditions in your workplace. It can be daunting. "Selection of the correct configuration and the right air-purifying elements really is a fairly complex process," says occupational hygienist Deborah Smith of Deborah Smith and Associates, in Edmonton, Alta.

To assist in the process, the Canadian Standards Association (CSA) has developed a standard Z94.4-93 Selection, Use, and Care of Respirators. "That should be the bible for the development of a respiratory protection program," says Narver. Greg Naherne, a hygienist and occupational health and safety consultant in Hamilton, Ontario, concurs. "The first thing to do [when selecting respiratory protection] is go to the CSA standard and follow that process," he says. The standard prescribes a procedure for respiratory selection. Among other steps, it recommends that the following factors be considered in the selection of a respirator:

* analysis of the airborne concentrations of contaminants;

* characteristics of the hazardous operation or process;

* period of time the respirator will be worn;

* type of work performed and the physical demands made on the worker;

* physical characteristics, functional capabilities and limitations of various types of respirators;

* respirator fit; and

* interaction with other protective equipment.

The CSA will soon be publishing a document to be used in conjunction with the standard, entitled Recommended Guide for a Respiratory Protection Program. "That guidance document is intended to be a user’s guide in layman’s language," explains Smith. It will explain how to comply with what the standard requires. The publication will be available in the first half of 1998, says Kevin MacKenzie, a project manager for CSA.

Although it set a standard for selection, use and care of respirators, the CSA does not certify respirators. It does, however, require that respirators meet the certification requirements of the U.S. National Institute for Occupational Safety and Health (NIOSH), the U.S. Mine, Safety and Health Administration (MSHA) or an equivalent group. Regulations in most provinces and territories require NIOSH approval for respirators. However, equipment approved by other regulatory authorities, such as those in Australia and New Zealand (AS/NZS standards), Japan (JIS standards) or Europe (EN standards), may also be acceptable for use here. It’s important to remember that differences exist among performance standards. If you are considering purchasing respiratory equipment with unfamiliar approvals, you should ask the supplier to explain exactly what that certification means and why the product hasn’t been certified in North America, advises Naherne. "You can then determine whether that’s a standard which is applicable in your case," he says.

NIOSH-certified respirators have an assigned protection factor (APF). This is another important consideration when selecting a respirator. For example, half-mask respirators have an APF 10, which means they can be used in concentrations up to 10 times the permissible exposure limit. You get greater protection from a full facepiece respirator than you do from a half facepiece respirator even if they use the same cartridges. This is because of the facepiece-to-face seal. A full facepiece has a larger sealing surface, explains Smith, "and it seals to a part of your face that is easier to seal than a half mask does." The seal for a full facepiece is around the part of your face that’s just below your hairline and under your chin. "That’s a smoother surface with fewer hills and valleys. So you can get a better fit," she says. And because that area is less likely to move due to speaking and facial gestures, the seal is less likely to be affected.

Nine new filter classes

The three-year transition period for the new National Institute for Occupational Safety and Health (NIOSH) rule regarding non-powered particulate filter air-purifying respirators and filters is about to end. Effective July 10, 1998, manufacturers may only sell respirators in that category that are certified under the new standard. Performance standards and the approval process for respirator certification in the United States are documented in the Code of Federal Regulation (CFR). The new rule, 42 CFR 84, establishes new performance criteria and new categories for non-powered particulate filter air-purifying respirators and filters. The rule will impact Canadian consumers because the majority of provinces and territories require NIOSH approval for respiratory equipment.

Single use dust/mist respirators, dust/mist/fume respirators, radon daughter respirators, pesticide pre-filters, and paint spray pre-filters have all been eliminated. These classes of respirators and filters have been replaced with nine new classes of filters. The classes are divided into three series of filters -- N, R and P -- each with three levels of filter efficiency: 95 per cent, 99 per cent, and 99.97 per cent. In addition to efficiency, selection depends on the presence or absence of oil particles and how long the filter will be in use. N-series filters can be used only with non-oil aerosols (N for Not resistant to oil). These filters have no recommended service life. R- and P-series filters can be used for both oil and non-oil aerosols. The R-series filters (R for Resistant to oil) have a service life of eight hours if used when oil aerosols are present. The P-series filters (P for oil Proof) can be used without time restrictions. Health care professionals should note that all nine classes meet or exceed The Centers for Disease Control and Prevention guidelines for respirator protection against tuberculosis.

NIOSH will address standards governing powered air-purifying respirators and other types of respirators, as well as performance characteristics such as face fit at a later date. (You can order the NIOSH User’s Guide to Selection and Use of Particulate Respirators Certified Under 42 CFR Part 84 from NIOSH Public Dissemination, 4676 Columbia Parkway, Cincinnati, Ohio, USA 45226-1998 or telephone NIOSH Publications at 513/533-8471. Request NIOSH Publication #96-101.)

You should also consider the amount of maintenance a respirator will require prior to making a selection. Models of respirators that have a permanent filter or cartridge are known as "maintenance free". Once the filter is plugged the entire respirator is thrown away. Other models have a variety of replaceable parts including the filters. These are described as full maintenance. Another option is a low-maintenance respirator, which has a facepiece with no replaceable parts but does have replaceable cartridges and/or filters. "Low maintenance models are generally significantly less expensive and quite a bit lighter," says Narver. However, you must consider more than just the initial cost. Consider how and when the respirator will be used and the quantity you’ll need, advises Naherne. A full-maintenance respirator may cost more to begin with but because it can be cleaned and repaired, it may be cheaper in the long run.

When it comes to dealing with manufacturers and distributors of respiratory equipment, "consumers should be extremely demanding," says Narver. Ask questions and be sure that you get them adequately answered, he says. "This is a product that could have life and death ramifications. You can’t be making respiratory selections without having all of the information that’s required."

"The bottom line," says Narver, "is never guess in respiratory [protection]. Always know what you’re dealing with."

Hayley Chandler is associate editor of safety purchasing for OHS CANADA.

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Is an air-purifying respirator the right choice?

In general, you can choose from two types of respirators: supplied-air and air-purifying. Supplied-air respirators provide breathable air from an outside source. With an air-purifying respirator, air is passed through a filter or cartridge that removes particles, vapours, gases or a combination of these contaminants. With non-powered types, the worker draws air into the respirator by inhaling. Powered types have a battery-powered fan that draws air through the filters and/or cartridges. However, neither type of air-purifying respirator supplies clean air independent of the workplace atmosphere. For this reason, air-purifying respirators will not provide adequate protection and should not be used in the following circumstances:

* If there’s a possibility of oxygen deficiency. (This includes confined spaces.)

* If a gas or vapour has poor "warning properties" (characteristics of a chemical -- such as odour, eye irritation and respiratory irritation -- that allow a worker to detect it). If a worker can detect a chemical while wearing a respirator, it is an indication that the respirator sorbent is spent, the facepiece is not fitted properly, or the respirator is malfunctioning. If a chemical has adequate warning properties, workers will be able to detect it at a concentration that is lower than the concentration at which it will cause damage. Remember that the ability of individuals to smell or taste contaminants can vary widely and some substances cause olfactory fatigue.

* In atmospheres immediately dangerous to life or health (IDLH). The CSA defines IDLH as "a condition in any work site, space, or area where a hazardous atmosphere exists to such an extent that a person without appropriate respiratory protection could be fatally injured or suffer immediate, irreversible, or incapacitating health effects."

* Where the concentration levels of a chemical are unknown.

* With certain specific substances, such as isocyonates.

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Buying Tips

Keep the following points in mind when selecting an air-purifying respirator.

* Get professional advice from a well-qualified occupational hygienist about the type of respiratory protection you need or get special training, advises Deborah Smith. This will not only help you determine your needs; it can help in choosing a supplier. "I think technical support is probably the most important factor in choosing a supplier," Smith says. However, "if buyers are not informed, they won’t recognize when they’re getting good technical support."

* "The distributor should offer a comprehensive respiratory training and fit testing program in concert with the manufacturer," says Jeff Narver.

* Look for a sales rep who can come in and explain things to workers, such as the use, maintenance, assembly, and cleaning of the respirator, says Greg Naherne.

* "You want to purchase from a supplier or distributor who stocks the bits and pieces that are necessary for maintenance," Naherne advises.

* Bring workers into the selection process. Manufacturers or distributors will often provide samples from which workers can choose. Ask for their opinions regarding comfort, resistance to breathing, interference with vision, interference with communication, and perceived effectiveness.

* "The wide range of face dimensions may require more than a single size, make, or model of respirator facepiece to provide a proper fit to all respirator users," says the CSA standard Z94.4-93 Selection, Use and Care of Respirators.

* Let workers try different brands of respirators, says Naherne. They may find some brands are easier to put on or to maintain than others. He also suggests letting people try different types of facepieces, as they may find certain materials are more comfortable than others.

* "You’ve got to also keep in mind how that respirator is going to fit together with other safety equipment," says Naherne. For example, will the respirator fit well with a welder’s helmet? Will it interfere with safety or prescription eyewear?

* Consider ease of maintenance. How easy is the respirator to take apart and put back together?

* A maintenance-free respirator is a good choice for very, very dirty applications when you don’t want to have to clean the respirator, says Narver. It is also often chosen for short-term projects.

* Note that it is possible to buy dust/mist masks that are not NIOSH/MSHA approved. These are often available to the general public at automotive supply stores. They are only intended to provide protection against nuisance levels of particulates and may not be have been tested by any group. They often have only one strap and do not provide an adequate face fit. "If it doesn’t have two straps, then it’s a mask not a respirator," says Narver. Always choose a respirator that’s been certified.

* A full-facepiece respirator provides protection against eye irritation in addition to providing respiratory protection.

* "A full-facepiece respirator can very, very easily be converted into supplied air if you need to. So it offers maximum flexibility," says Narver.

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