The basic purpose of any respirator is to protect the wearer from inhalation of hazardous materials/atmosphere. Respirators provide protection either by removing contaminants from the air before inhalation or by supplying an independent source of clean air. These principles delineate the two basic respirator types.
A device that removes contaminants from the ambient air is called an air-purifying respirator (APR). These devices operate under negative pressure created through inhalation. This negative pressure allows contaminated air through purifying elements and into the face piece. A device that provides a clean source of breathable air independent of ambient air is called an air-supplying respirator (ASR). These devices operate under positive pressure created by the external air source. Both can be sub classified by the type of inlet covering and the mode of operation.
The inlet covering serve as a barrier against contaminated atmospheres and as a framework to which air-purifying or air-supplying elements are attached.
Tight-Fitting Respirators
Tight-fitting coverings or face pieces are made of flexible materials such as butyl rubber, silicone, or neoprene. The face pieces are held on by the use of rubber or elastic straps which buckle at the back of the head.
These face pieces are of three basic configurations. A quarter-face covers just the mouth and nose and the lower sealing surface rests above the chin. These are typically used for protection against nuisance particulates or very low concentrations of known contaminants.
A half-face mask covers the nose, mouth and chin. These provide a larger sealing surface than the quarter-mask and are preferred for use against more toxic materials. Both of the above devices provide no eye protection.
The third type of tight-fitting device is the full-face respirator. This mask covers the area from the hairline to below the chin.
Because of this large sealing surface they provide the greatest degree of respiratory protection, provide some degree of eye protection and are the most commonly used of the three types.
Mouthpiece respirators are the most basic types of device and consist of a nose clamp and mouthpiece that is held in the teeth. These devices prevent verbal communication, may cause fatigue of the jaw and provide no eye protection. Therefore they are restricted for use as escape devices.
Loose-fitting Respirators
These devices include hoods, helmets, suits and blouses. At a minimum, they must enclose the head and when the neck and shoulders are included consist of a hood. A helmet incorporates a rigid headgear into the design and a blouse extends down to the waist and may include wrist-length sleeves. These are typically used for abrasive blasting and hood/helmet materials are designed to withstand rebounding particules. Compressed air breathing sources are normally used and headgear include an impact resistant eye-shield for protection against abrasive particles.
Air-purifying Respirators
1. Particulate Filtering APR's
These are used for protection against dusts, mists, and fumes. A dust is a mechanically generated solid particulate, a mist is a liquid condensation particulate and a fume is a solid condensation particulate usually produced from vaporized solids.
Most particulate filtering devices use fibrous materials to remove the contaminant. As a particule is drawn into the filter through inhalation, the filter media traps it. The efficiency of the filter depends on the size, velocity and composition of the particle. As particles are captured in the media it becomes clogged. This loading process can potentially increase the collection efficiency of the filter, but also increases the breathing resistance eventually requiring replacement of the filter cartridge.
Current filter manufacturers utilize five mechanisms in particle capture. These include interception, sedimentation, impaction, diffusion and electrostatic capture.
During interception, the filter media captures particulates as they are carried in the inhaled air stream. Sedimentation occurs in large particles (>2 u) where the effects of gravity pull particles from the air stream.
Inertial impaction occurs as particles are drawn into the filter media and are too large or heavy to change directions and avoid capture.
Diffusion occurs in very small particles subject to collision with air molecules.
These collisions cause random motion among the particulates increasing the chances of capture by the media.
In electrostatic capture, the filter media is charged which attracts particulates and aids in capture through interception and diffusion.
All of these mechanisms are affected by particulate size and weight, velocity, composition and environmental conditions. In general large, heavy particles are usually removed by inertial impact and interception. Large, light particles are removed by diffusion and interception. Diffusion can also remove very small particulates.
The filter media for particulate capture includes three basic types. The most common is the flat disk of random laid, non-woven fiber material which is designed to provide maximum natural collection with minimum resistance. Other types include natural wool or synthetic blend felt to which an electrostatic charge is applied. A disadvantage to this type is the loss of the charge due to oily atmospheres, high humidity and age. A sticky resin can also be applied to the fiber material causing particules to adhere to the filter pad. Finally a high efficiency particulate air (HEPA) filter has been developed for protection against radioactive particles, asbestos fibers and other carcinogenic particulates considered respirable (<10 u).
The following types of particulates respirators are certified for use by NIOSH/MSHA and 老澳门资料.
- Replaceable or reusable dust and mist respirators designed for protection against (1) dusts and mists with a permissible exposure limit (PEL) <0.05 milligrams per cubic meter (mg/m3) of air, (2) dust and mists having a PEL <2 million particles per cubic foot (mppcf) of air.
- Replaceable fume filters designed as respiratory protection against fumes of various metals having a PEL <0.05 mg/m3.
- Respirators with replaceable filters for protection against dusts, fumes and mists of materials with a PEL <0.05 mg/m3 or 2 mppcf (for combination cartridges).
- Single use respirators designed for nuisance dusts and mists can be used if either the filter or the entire face piece is disposable. These respirators are not to be used for protection against asbestos, highly toxic or radioactive particulates.
2. Gas and Vapor Removing APR's
These devices are used for protection against the other major class of airborne contaminants; gases and vapors. APR's are commercially available for specific gases/vapors (i.e. ammonia gas and mercury vapor) and classes of gases/vapors (i.e. acid gases and organic vapors).
Unlike particulates filtering devices which are effective against particulates as a whole, the cartridges used in gas/vapor removal are designed to be specific for known contaminants.
These respirators are fitted with cartridges or canisters containing a granular material commonly referred to as sorbent. The general method by which removal occurs is called sorption. Three specific mechanisms are used in the sorption of gases/vapors.
- Absorption retains the contaminant on the surface of the sorbent granules by physical attraction. Activated charcoal is the most common absorbent used in this mechanism. If chemical attraction is necessary (chemisorption), the charcoal can be impregnated with other substances to make it more selective against specific gases/vapors. For example activated charcoal impregnated with iodine removes mercury vapors, with metallic oxides removes acid gases, and with salts or metals removes ammonia gas. Other sorbents include molecular sieves, activated alumina, and silica gel.
- Absorption may also be used to remove gases/vapors. Absorbents collect contaminants by allowing penetration deep into the pores of the sorbent where chemical bonding holds them. Most absorbents are used for protection against acid gases. These include mixtures of sodium or potassium hydroxide with lime and/or caustic silicates.
- Catalysis is the third method of gas/vapors removal. A catalyst is a substance that influences the rate of chemical reactions and can cause them to occur more readily. An example of a catalyst used in respirator cartridges is Hopcalite, a mixture of manganese and copper oxides, which speeds the reaction between carbon monoxide and oxygen to form water vapor and carbon dioxide. These cartridges have a relatively short lifespan and are subject to damage from moisture buildup.
In contrast to mechanical filters which become more efficient with use, sorbent cartridges reach a saturation point where breakthrough occurs allowing contaminants into the face piece. Therefore it is recommended that they be protected from the environment while not in use as interaction with the air will speed saturation.
Some respirators utilize canisters instead of cartridges. In general, canisters are larger than cartridges, contain more sorbent and can be used against higher contaminant concentrations. Cartridges are chin mounted usually in pairs while canisters can be chin, front or back mounted and connected to a flexible breathing hose. The canisters are typically certified for single or specific classes of gases/vapors and respirators utilizing them are commonly called gas masks.
Since the majority of workplaces involve more than one type of respiratory hazard, respirators are usually equipped with combination cartridges.
These cartridges are capable of removing both particulate and gas/vapor air contaminants and are available from most manufacturers.
A specialized type of combination cartridge is the Type N or Universal canister. It is similar to the larger front or back-mounted canister but contains several layers of sorbent materials. These include media for ammonia, acid gas, organic vapors, a catalyst for carbon monoxide and a HEPA filter for asbestos and radioactive particles. Because the Type N canister is the same size as normal canisters and therefore offers limited space for each sorbent layer, it has a shorter lifespan than conventional canisters.
All canisters approved for use against carbon monoxide must have an indicator that shows when the canister is spent. The indicator actually shows the condition of the drying agent upstream of the catalyst. The catalyst is rendered useless by moisture which stops the chemical reaction and clogs the cartridge.
3. Powered Air-Purifying Respirators (PAPR)
These devices remove airborne contaminants through the same mechanisms as non-powered APR's but utilize a small blower to provide a degree of positive pressure in the face piece. The purifying element may be filter to remove particulates, a cartridge to remove gases/vapors or a combination cartridge to remove both.
PAPR's come is several configurations including those with belt-mounted cartridges and blower on chin mounted cartridges and blower. A third type of PAPR consists of a loose fitting helmet or hood and face piece. Purified air is circulated over the face and out under the face piece. These devices utilize a small, rechargeable battery pack usually worn at the belt to power the blower. The tight fitting half and full-face PAPR's must deliver at least four cubic feet of air per minute or ll5 liters per minute (Lpm). The hood or helmet PAPR's must deliver more air, at least six (170 Lpm), because they are loose fitting and the potential for leakage is greater.
PAPR's are sometimes preferred over APR's because they supply a source of positive pressure and allow use in higher contaminant concentrations. They also tend to keep the wearer cooler and less fatigued. This is due to the increased air movement in the mask and the decreased effort required for inhalation. However, one disadvantage of PAPR's is the potential for shorter cartridge life spans also due to the positive pressure aspect.
4. Advantages and Disadvantages of APR's
- APR's are generally small and easily maintained. They can restrict the wearer's movements but not as much as other protective devices. Communications and visual field are restricted which can result in decreased ability to accomplish job functions and increase the probability for accidents.
- Therefore care must be taken during use. The many combinations of mouthpieces, face pieces, filters, cartridges and canisters allow the user to match the respirator to the particular situation and ensure proper fit.
APR's cannot be used in oxygen deficient atmospheres (<19.5%) nor in atmospheres immediately dangerous to life and health (IDLH). Further, the limits of airborne contamination are listed on the cartridge and should not be exceeded as breakthrough can occur. This means that the type and properties of the contaminants must be known and that air monitoring may be required to confirm these conditions before a respirator can be used.
Another important consideration is the negative pressure created in the face piece during inhalation. This would allow contaminants inside the mask should a leak or improper fit occur. Care should be taken to provide a respirator that is fitted to the wearer and training to ensure proper donning and adjustment.
- Particulate filtering respirators have the advantages of light weight, small size and ease of maintenance. In general they will not affect the mobility of the wearer and present little physiological strain. The resistance to breathing is minimal at first but may increase as the filter becomes loaded. The dirtier the work setting, the quicker the filter becomes loaded and the sooner the filter must be replaced. The filter elements should be replaced as breathing resistance becomes excessive or if the filter suffers physical damage. Filter elements should be cleaned and reused if so designed and stored to prevent exposure to the environment. The wearer must also know the type of particulate to ensure proper filter selection.
- Gas/Vapor removing respirators have the same advantages as particulate filtering devices in size and weight. However, certain cartridges/canisters have higher breathing resistance than filters and therefore cause an increased burden on the wearer. Like filters, cartridges/canisters are subject to degradation from the environment. Extremes in humidity can cause clogging and interrupt the chemical reactions occurring in the cartridge.
- Unlike filters, cartridges/canisters have a sorbent material which becomes spent or saturated with use. This can occur rapidly in high concentrations and allow contaminants into the face piece. For this reason, it is crucial that the wearer be familiar with the type of contaminant and its warning properties. These properties include odor, taste and eye, throat or facial irritations. If these properties are detected during use, the wearer must exit the area to a clean environment and replace the cartridge. If a wearer detects one of these properties and then the sensations disappear, cartridge replacement should still occur. Many compounds can cause fatigue of nerve endings and dull the senses (olfactory fatigue). This is especially common during continued exposure to low concentrations. It is not an indication that the exposure has ceased.
- In addition to warning properties, users should institute a regular change-out schedule for cartridge replacement. These schedules should be based on the contaminant concentrations and the cartridge service-life data available from the respirator manufacturer. Users should replace cartridges/canisters when warning properties are detected, if damage occurs or when the change-out schedule indicates.
- PAPR's have the advantage of providing an air stream to the wearer. This tends to provide a cooling effect and decreases breathing resistance thereby making the respirator more comfortable to wear. PAPR's with loose fitting headgear are also more comfortable and can sometimes be used by those with facial hair or other restrictions applicable to tight fitting PAPR's.
- Disadvantages include those common to all APR's such as bulkiness, decreased visibility and communications. PAPR's also have additional considerations of battery replacement and mechanical failure. If the blower should stop, the user should leave the work area and proceed to a clean area for repairs/replacement. Finally, PAPR's are more expensive to purchase and maintain than APR's.
B. Air Supplying Respirators
These devices are designed to provide a clean source of air regardless of the working environment and are specially designed to protect employees from hazardous atmospheres at greater concentrations than APR's. Because of this distinct advantage the use and care of these devices are more restrictive.
1. Self-Contained Breathing Apparatus (SCBA)
These devices allow the user to be provided with clean breathing air independent of external sources. The wearer does not have to rely on or be limited by stationary air sources such as an air compressor. Enough breathable air is carried by the user to last up to four hours depending on the design of the unit. SCBA's are classified by mode of operation into two types, closed circuit and open circuit.
- Closed-circuit SCBA's, or rebreathers as they are sometimes called, allow recirculation or breathing air. Exhaled air is scrubbed to remove carbon dioxide and a compressed or liquid source, or an oxygen-generating solid restores the oxygen content.
These devices are designed primarily for 1 - 4 hour use in oxygen deficient or IDLH atmospheres.
Until recently, all closed circuit SCBA's were non-positive devices meaning negative pressure is created during inhalation. Therefore, they should be restricted for use during activities requiring long-term, uninterrupted protection.
The most common type of closed circuit SCBA utilizes a compressed oxygen source supplying an inflatable bag. Exhaled air passes through a sorbent that removes carbon dioxide and the air is returned to the bag. Thus only consumed oxygen is replaced by the compressed source. This rebreathing process requires only oxygen be replaced and allows long-term protection.
Another type of closed circuit SCBA uses an oxygen-generating solid such as potassium super oxide. Oxygen is not released until the exhaled breath reaches the canister. Water vapor and carbon dioxide in the breath react with the potassium super oxide releasing oxygen. This unit provides a positive pressure in the face piece as oxygen is continually released into reservoir bags once the reaction is initiated. This type of device is lighter and simple than the cylinder type, but typically has a one-hour supply of oxygen that cannot be turned off once initiated.
- An open-circuit SCBA allows exhaled air to exhaust without recirculation. Another basic difference is that only compressed is used in the cylinder, NOT compressed oxygen. High-pressure cylinders (2000-45000 psi) supply compressed air through a regulator that reduces the pressure to the face piece. Expected service life ranges from 30-60 minutes depending on the size of the cylinder. Two common cylinder types are available and include steel and spun fiberglass around an aluminum core. The steel is more durable, but weighs more and must be hydrostatically tested every five years. The composite is lighter, but must be hydrostatically tested every three years and is more susceptible to physical damage.
Two modes of open-circuit SCBA operation are currently available, demand and pressure-demand. In the demand mode, air from the regulator is not released until the wearer inhales creating negative pressure in the face piece. Due to this negative pressure and the possibility of leakage into the mask, demand SCBA's should not be used in IDLH atmospheres. However, they are adequate for oxygen-deficient atmospheres.
In the pressure-demand mode of operation, a positive pressure is maintained in the face piece at all times. Because of this positive pressure, any leakage will be outward. Therefore, a pressure-demand SCBA provides very good protection and can be used in either IDLH or oxygen deficient atmospheres. This mode of operation allows the same service life as that expected from the demand unit unless a poor fit is achieved or leakage occurs.
Some open-circuit SCBA's can be switched from demand to pressure-demand modes during fit and adjustment. This donning switch allows the face piece to be put on without loss of breathing air in the demand mode. However, once the mask is donned and adjusted properly, the unit should be switched to the pressure-demand mode to insure maximum protection during use.
Several required safety features are found on SCBA's certified by NIOSH or MSHA. These include:
- a pressure gauge visible to the wearer during use indicating the remaining air supply
- a warning device indicating remaining service life at 20-25% capacity of the cylinder
- a bypass valve in case the regulator fails and it is necessary to conserve or continue air flow
- fittings and connections that are not compatible with compressed oxygen or liquid air devices.
Areas using SCBA equipment on a regular basis should set up a charging station. Where units are used for emergency situations, local distributors can arrange for charging. when an area does not have a method for cylinder charging, enough spare cylinders should be available to deal with emergency situations. When charging is feasible, the cascade system of refilling cylinders is the easiest to use. It is based on the equalization between large cylinder supply tanks and the smaller SCBA tank.
Usually, two or more supply tanks of respirable air are connected in series through tee-block fittings and pigtails. A manifold outlet is connected to the last cylinder complete with high pressure gauge. A 5-foot length of high-pressure hose with an air fitting is used to connect the SCBA tank to the manifold.
To fill the SCBA:
- i. Check the date of the hydrostatic testing on the tank to make sure it is current. Check the pressure in the SCBA cylinder by observing the pressure gauge on the main valve. If the cylinder has no gauge, the pressure may be checked by slowly opening the main valve and observing the pressure gauge on the system outlet valve. Close the cylinder man valve.
- ii. Open and close each valve in the supply cylinder bank to find the cylinder with the lowest pressure. If the pressure in this cylinder is not greater than in the cylinder to be charged, locate the supply cylinder with a pressure higher than that of the SCBA cylinder but lower than the other supply cylinders.
- iii. Slowly open the valve on the SCBA cylinder. Then, slowly open the valve on the supply cylinder with the lowest pressure as determined in step 2. Observe the outlet connection gauge. When the pressure of that gauge stops dropping, the pressures in the two cylinders have equalized. Close the supply cylinder valve. If the desired pressure in the SCBA cylinder has not been reached, repeat the procedure using he cylinder with the next highest pressure.
- iv. If the last supply cylinder does not fully recharge the SCBA cylinder, replace the supply cylinder having the lowest pressure with a full cylinder and repeat steps 2 and 3. Once the SCBA cylinder is full, close all valves in the system and disconnect the SCBA cylinder.
The major advantage of SCBA use is the freedom of movement allowed by wearing the supply of breathing air on the back. However the bulk and weight of the unit may prevent strenuous work or confined work. The limited supply of air makes them unsuitable for long, continuous periods unless repeated tank changes can be made.
2. Airline respirators
These devices supply compressed breathing air from a stationary source delivered through a length of hose under pressure. They are available in demand, pressure demand, or continuous flow modes provided through a face piece, helmet, hood, or complete suit.
Breathing air is supplied from cylinder or an air compressor. OSHA specifies that the pressure supplied to the hose not exceed 125 pounds per square inch (psi) and that the hose length be between 25 and 300 feet. For a hood or helmet device with 300 feet of hose OSSA requires at least 170 liters per minute (Lpm) of airflow be delivered to the wearer. For a hood or helmet with 25 feet of hose OSHA would require no more than 425 Lpm. The equivalent airflows to a tight-fitting face piece are 115 and 425 Lpm, respectively. These limitations are given as required specifications in the design of airline respirator systems.
Continuous-flow airline respirators maintain a constant flow of breathing air to the wearer at all times, rather than only on demand. OSHA requires a flow of at least 115 Lpm to a tight fitting mask and 170 Lpm to a hood or helmet. This continuous flow of positive pressure provides high protection, but also requires a larger supply of air.
3. Hose masks
These devices supply air from an uncontaminated source through a strong, large diameter hose. Two types are available. One utilizes an electric or hand powered blower that pushes low-pressure air through the hose to the wearer. If for some reason the blower was to fail, the wearer can still breathe through the large diameter hose. The other type does not have a blower and the wearer must simply breathe through the hose. The hose mask with the blower is classified by OSHA as a Type A supplied-air respirator and is certified for use in atmospheres that are not IDLH. This unit may have up to 300 feet of air hose in multiples of 25 feet and be able to deliver air through the hose at not less than 50 Lpm and not more than 150 Lpm. This device may be fitted to a hood, helmet, or tight-fitting face piece. The hose mask without a blower is a Type B respirator and is also certified for use in non-IDLH atmospheres. The length of hose is limited to 75 feet in multiples of 25 feet. This device may only be fitted to tight-fitting face piece.
Because these units do not provide high pressure inside the face piece they afford a low degree of protection and are not widely used in industrial applications.
4. Combination supplied-air/air-purifying respirators
These devices are available and have been approved for use by NIOSH/MSHA. These units are classified as Type C and are certified under the type of air-purifying element attached as it is the component that affords the least protection to the wearer. The device consists of a face piece, regulator, breathing tube, belt or harness, supplied-air hose, and air-purifying element. This element can be a canister, cartridge, or particulate filter. It is mounted either directly on the face piece or on the belt.
The supplied-air portion of the unit can be either demand or pressure-demand. The advantage of this type of device is the ability to enter and leave an area without the airsupplied portion and the associated hardware. Additionally, should the air supply fail, the unit can be used in the air-purifying mode for escape purposes. Limitations include those common to all air-purifying units such as specific protection against known agents and prohibited use in oxygen deficient and IDLH atmospheres.
Restrictions will also apply depending on the type of air-purifying element used, but may include:
- No restrictions
- unit can only be used to enter an area prior to connection to the air
- supply or exiting an area following disconnection or loss of air supply
- escape only after loss of air supply.
5. Combination supplied-air/SCBA respirators
These devices are available for use in IDLH atmospheres. This is possible using an airline respirator with the addition of an auxiliary air supply to protect against failure of the primary air supply. The auxiliary air supply is provided by adding a selfcontained cylinder of compressed air. This auxiliary air supply may be certified for 3-, 5-, or 10-minute service life spans or for 15 minutes or longer. Because of this short service life, these units are commonly used for escape from IDLH atmospheres or for emergency rescue operations.
The breathing air used in compressed sources such as SCBA's compressors and cylinders must meet minimum quality standards set forth by the Compressed Gas Association (CGA) in Specification G7.1. The breathing air shall be at least a Grade D or equivalent. The following table summarizes the required parameters for Grade D air. OSHA requires that the source of this air be tested every six months for these parameters. EH&S is available for assistance in conducting this testing.
Oxygen content: 19% - 23%
Carbon Monoxide: 10 ppm
Carbon Dioxide: 1000 ppm
Oil mist: 0.005 mg/1
Total Hydrocarbons: 25 ppm
Halogenated solvents: 0.2 ppm
Total moisture: 0.3 mg/1
When an air compressor is used for breathing air, a trap and carbon filter must be installed to remove oil, water, scale, odor and taste; a pressure reducing valve must be installed to reduce air pressure to respirator requirements; and an automatic shutoff must be in place to either sound an alarm or stop the compressor in the event of overheating. Specially designed breathing air compressors are commercially available with the above criteria.
Compressed gas cylinders may also be used in the absence of a compressor with the air quality requirements remaining the same.
A regulator must be in-line to reduce the pressure to respirator requirements. However, constant flow respirators are not recommended, as the air supply is limited to the volume of the cylinder.
C. Respirator Selection Criteria
Respirators must be selected on the basis of the hazards to which employees may be exposed. The following information is provided to assist in the decision process for selecting the proper respirator type and assuring adequate protection.
In cases where OSHA has specified a specific respirator be used for a certain task or substance (such as asbestos or other carcinogens) that respirator or one providing equal or better protection must be used. This can be determined by reference to the specific health standard or reviewing the Material Safety Data Sheet (MSDS) for that substance. In all cases where respirator selection or use is questioned, contact EH&S.
Decision Considerations
- What is the contaminant concentration expected through estimation or air monitoring? This will aid in determining the need for APR's or ASR's.
- What is the permissible exposure limit (PEL), threshold limit value (TLV), or shortterm exposure limit (STEL) of the contaminant. Also note the potential for skin absorption as indicated on the MSDS, TLV or PEL lists. Used to determine the need for respiratory or other protective equipment.
- Is the contaminant a gas, vapor, mist, dust or fume? This can be obtained from the MSDS and the properties of the raw material. This is used to determine the type and availability of the removal method the respirator will need.
- Could the contaminant concentration reach that immediately dangerous to life and health (IDLH)? This information can be obtained from the MSDS and should include the possibility of occurrence during a spill or release. Will be used in emergency response procedures.
- If the contaminant is flammable, does the estimated working concentration approach the lower explosive limit (LEL) as given on the MSDS? Does the dust create an explosion potential? In most cases concentrations approaching the LEL are also IDLH. Consideration should also be given to potential explosive conditions during spills.
- Does the contaminant have good warning properties? Information on odor, taste and irritations can be obtained from the manufacturer or the MSDS. These properties should be known to recognize leakage and potential exposure during APR use.
- Will the contaminant irritate the eyes at the expected working concentration? This information can be obtained from the MSDS or previous experience and is used in the selection of full-face or half-face APR's.
- What respirator(s) will give the required maximum use concentration (MUC)? Determination is made by multiplying the contaminant PEL by the protection factor (PF) for the respirator of choice (as given in the following table). IF the maximum expected working concentration of the contaminant is less than the MUC for that respirator then an acceptable choice has been made.
MUC = PEL X PF
TABLE I. ASSIGNED RESPIRATOR PROTECTION FACTORS PER ANSI Z88.2 1992
| Protection Factor |
Type of Respirator |
| 10 |
Single-use or Quarter-mask APR |
| 10 |
Half-mask APR or Half-mask ASR in demand mode |
| 25 |
PAPR with hood/helmet, continuous flow ASR withhood/helmet (loose fitting) |
| 50 |
Half-face PAPR, Half-face ASR in pressure demand mode, half-mask ASR in continuous flow mode |
| 100 |
Full-face APR, Full-face ASR in demand mode |
| 1,000 |
Full-face ASR in pressure demand mode or continuous flow mode, Full-face and loose fitting PAPR with HEPA-filter |
| 10,000 |
Full-face SCBA in pressure demand or positive pressure mode, full-face ASR with auxiliary SCBA in pressure demand or positive pressure mode. |
Respirators should be assigned on an individual basis. Employees should be responsible for assuring that their equipment is kept clean, sanitary and in good working condition. The respirators should be marked with the employee's I.D.
Routine use of respirators means daily or frequent use on a regular basis. For such use, a respirator of low initial cost, simple maintenance, minimal wearing discomfort and compact construction should be considered.
A respirator used non-routinely is used for hazardous situations that occur occasionally. For such applications, initial costs and maintenance costs are less important than for routine applications. The degree of protection and the useful service life provided are important.
A manufacturers' equipment is acceptable if it has been approved for use by the National Institute for Occupational Safety and Health/Mine Safety and Health Administration (NIOSH/MSHA) for the exposure of concern. Reputable distributors should be contacted for pricing and availability to ensure that outdated or unapproved equipment is not purchased. Purchasers should specify to vendors that only NIOSH/MSHA approved equipment will be accepted. Such equipment will have a special logo on the packaging material along with an approval number (TCnumber). Most laboratory equipment suppliers carry personal protective equipment or you may contact EH&S for additional suppliers.
All component and replacement parts must also carry this approval. In addition, respirators are approved as a system. Cartridges, canisters, filters, air lines, and regulators cannot be interchanged between manufactures.
