A Negative Pressure Respirator Brings

Question: Introduction
Answer: On a hazardous waste site, many different types and levels of inhalation hazards exist. Waste site workers need to thoroughly understand the different types of respiratory equipment available, protection factors, and fit testing so they can select the best respirator for the hazards they will encounter.
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Question: 29 CFR
Answer: Under 29 CFR 1910.134, OSHA requires employers to have a respiratory protection program that covers all employees whose job requires the use of respirators. This program must meet the following requirements:
1. Respirators will be selected based on hazards to which the worker is exposed.

2. The user will be instructed and trained in the proper use of respirators and their limitations.

3. Written standard operating procedures covering the selection and use of respirators must be established.

4. Respirators must be regularly cleaned and disinfected. Those used by more than one worker must be thoroughly cleaned and disinfected after each use.

5. Respirators used routinely will be inspected during cleaning. Worn or deteriorated parts will be replaced.

6. Respirators will be stored in a convenient, clean, and sanitary location.


7. Appropriate surveillance of work area conditions and degree of employee exposure or stress shall be maintained.


8. The user should be properly fit tested and taught how to check face-piece fit before each use.


9. The employer, through medical evaluations, will determine if a user is physically able to perform the work and use the equipment. This medical status should be reviewed periodically, when conditions change, or the program administrator, PLHCP, or supervisor recommends re-evaluation.


10. The effectiveness of the program should be evaluated on a regular basis.
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Question: Selection of Respiratory Equipment
Answer: Respiratory protection is of primary importance since inhalation is one of the major routes of exposure to chemical toxicants. Respiratory protective devices (i.e., respirators) consist of a face-piece connected to either an air source or an air-purifying device.
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Question: Positive Pressure Airflow
Answer: Positive-pressure respirators maintain a positive pressure in the face-piece during both inhalation and exhalation. The two main types of positive-pressure respirators are pressure-demand and continuous flow.
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Question: Pressure-Demand
Answer: In pressure-demand respirators, a pressure regulator and an exhalation valve on the mask maintain the mask's positive pressure, except possibly during high breathing rates. If a leak develops in a pressure-demand respirator, the regulator sends a continuous flow of clean air into the face-piece, preventing penetration by contaminated ambient air.
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Question: Continuous-Flow
Answer: Continuous-flow respirators including some supplied air respirators (SARs) and all powered air-purifying respirators (PAPR), send a continuous stream of air into the face-piece at all times. With SARs the continuous flow of air prevents infiltration (i.e., invasion) by ambient air but uses the air supply much more rapidly than with pressure demand respirators. Powered air-purifying respirators (PAPRs) are operated in a positive-pressure continuous flow mode utilizing filtered ambient air. However, maximum (i.e., highest) breathing rates can create a negative pressure in the face-piece of a PAPR.
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Question: Negative-Pressure Airflow
Answer: Negative-pressure respirators draw air into the face-piece via the negative pressure created by user inhalation. The main disadvantage of negative-pressure respirators is that if a leak develops in the system (i.e., a crack in the hose or an ill fitting mask or face-piece), the user draws contaminated air into the face-piece during inhalation. When atmosphere-supplying respirators are used, only those operated in the positive-pressure mode are recommended for work at hazardous waste-sites.
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Question: Atmosphere Supplying Respirators
Answer: Atmosphere-supplying respirators are respirators with an air source and consist of two types:
Self-contained breathing apparatus (SCBA) supplies air from a source carried by the user.

Supplied air respirator (SAR) supplies air from a source located some distance away and connected to the user by an air line hose. Supplied air respirators are sometimes referred to as air line respirators.
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Question: Air Purifying Respirators
Answer: Air-purifying respirators (APRs), on the other hand, do not have a separate air source. Instead, they utilize ambient (i.e., surrounding) air which is "purified" through a filter before inhalation.
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Question: Types of Face Pieces
Answer: Different types of face-pieces are available for use with various types of respirators. The types generally used at hazardous waste sites are full face-piece masks and half masks. Full face-piece masks cover the face from the hairline to below the chin, providing eye protection. Half masks cover the face from below the chin to over the nose and do not provide eye protection.
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Question: Testing
Answer: Federal regulations require the use of respirators that have been tested and approved by the Mine Safety and Health Administration (MSHA) and NIOSH. Testing procedures are described in 29 CFR 1910.134 Appendix A. Approval numbers are clearly written on all approved respiratory equipment. However, not all respiratory equipment that is sold is approved. Periodically, NIOSH publishes a list, entitled NIOSH Certified Equipment List, of all approved respirators and respiratory components.
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Question: At Sites
Answer: At sites where the identity and concentration of chemicals in the air are known, a respirator should be selected with a protection factor that is sufficiently high to ensure that the wearer will not be exposed to the chemicals above the applicable limits. These limits include:
American Conference of Governmental Industrial Hygienists threshold limit values (TLVs)

OSHA's permissible exposure limits (PELs)

NIOSH's recommended exposure limits (RELs)
These limits are designed to protect most workers who may be exposed to chemicals day after day throughout their working life. OSHA PELs are legally enforceable exposure limits and are the minimum limits of protection that must be met.

Remember that the protection provided by a respirator can be compromised (i.e., threatened) in several situations, most notably:
If a worker has a high breathing rate

If the ambient temperature is high or low

If the worker has a poor face-piece-to-face
At high breathing rates, positive-pressure SCBAs and SARs may NOT maintain positive pressure for brief periods during peak inhalation. In addition, at high work rates, exhalation valves may leak. Consequently, positive-pressure respirators working at high flow rates can offer less protection than when working at normal rates.
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Question: Air Purifying Respirators 2
Answer: Air-purifying respirators consist of a face-piece and an air purifying device. The air-purifying device is either a removable component of the face-piece or an apparatus worn on a body harness and attached to the face-piece by a corrugated breathing hose. APRs selectively remove specific airborne contaminants (particulate, gases, vapors, and fumes) from ambient air by filtration, absorption, adsorption, or chemical reactions.

APRs are approved for use in atmospheres containing specific chemicals up to designated concentrations. APRs are NOT approved for IDLH (immediately dangerous to life and health) atmospheres. Air-purifying respirators have limited use at hazardous waste sites and can be used only when the ambient atmosphere contains sufficient oxygen that is, greater than 19.5 percent oxygen (30 CFR Part 11.90(a)). Air-purifying respirators usually operate only in the negative-pressure mode except for powered air-purifying respirators (PAPRs), which maintain a positive face-piece pressure (except at maximum breathing rates).

There are three types of air-purifying devices:
Particulate filters

Cartridges and canisters, which contain sorbents for specific gases and vapors

Combination devices
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Question: Cartridges and Canisters
Answer: Combination canisters and cartridges contain layers of different sorbent materials and remove multiple chemicals or multiple classes of chemicals from the ambient air. Though approved for more than one substance, the combination canisters and cartridges are tested independently against single substances. Thus, the effectiveness of these canisters against two or more substances has not been demonstrated.

Filters can also be combined with cartridges to provide additional protection against particulates. A number of standard cartridges and canisters are commercially available. They are color coded to indicate the general chemicals or classes of chemicals against which they are effective (29 CFR Part 1910.134(g)).
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Question: Respirators - more info
Answer: Respirators should be used only for those substances for which they have been approved. For a limited number of specific chemicals, MSHA and NIOSH have granted approvals for manufacturers' specific assemblies of air-purifying respirators. It should be noted that approval testing is performed at a given temperature and over a narrow range of flow rates and relative humidity levels; thus, protection can be compromised in nonstandard conditions.

The assembly that has been approved by MSHA and NIOSH to protect against organic vapors is tested against only a single challenge substance--carbon tetrachloride. Therefore, the assembly's effectiveness in protecting against other vapors has not been demonstrated.
The efficiency of APRs varies considerably, even on closely related materials. Use of a sorbent shall NOT be allowed when there is reason to suspect that it does not provide adequate sorption efficiency against a specific contaminant.
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Question: Adequate Warning Properties
Answer: If a canister or cartridge is to be used against gases or vapors, the appropriate device shall be used only if the chemical(s) have adequate warning properties per 30 CFR Part 11.150. NIOSH considers a substance to have adequate warning properties when:

Its odor, taste, or irritant effects are detectable and persistent at concentrations below the recommended exposure limit (REL).

A substance is considered to have poor warning properties when:

Its odor or irritation threshold is above the applicable exposure limit.
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Question: Sorbent Exhaustion
Answer: The respiratory standard has been changed to emphasize that contaminant breakthrough should not be relied upon as a signal, or indicator, of possible sorbent exhaustion. Canisters or cartridges should be changed out in accordance with a change schedule. Change schedules can be obtained through the OSHA web site, manufacturer's schedule, and trade associations; if these are not applicable, then according to the company's policy.

OSHA permits the use of air-purifying respirators for protection against specific chemicals with poor warning properties provided that one of the following is true:
The service life of the sorbent is known and a safety factor has been applied.

The respirator has an approved end-of-service life indicator.
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Question: Self-Contained Breathing Apparatus
Answer: A self-contained breathing apparatus (SCBA) usually consists of a face-piece connected by a hose and a regulator to an air source (compressed air, compressed oxygen, or an oxygen-generating chemical) carried by the wearer.
SCBAs offer protection against most types and levels of airborne contaminants. However, the duration of the air supply is an important planning factor in SCBA use. This is limited by the amount of air carried and its rate of consumption. In addition, SCBAs are bulky and heavy; thus, they increase the likelihood of heat stress and can impair movement in confined spaces. Under MSHA regulations in 30 CFR Part 11.70(a), SCBAs can be approved for both entry into and escape from a hazardous atmosphere, or escape only.
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Question: Escape only SCBA Respirators
Answer: Escape-only SCBAs are frequently continuous-flow devices with hoods that can be donned to provide immediate emergency protection. Employers should provide and ensure that employees carry an escape SCBA where such emergency protection can become necessary.
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Question: Entry and escape SCBA Respirators
Answer: Entry-and-escape SCBA respirators include air tanks worn by workers. Entry-and-escape SCBAs give workers undeterred (i.e., unrestricted) access to nearly all portions of the worksite. However, they decrease worker mobility, particularly in confined areas, because of their bulk and weight. Their use is particularly advisable when dealing with unidentified and un-quantified airborne contaminants. Generally, SCBAs are required for workers operating in oxygen-deficient atmospheres (under 19.5 percent), in contaminated zones, and in atmospheres that are immediately dangerous to life and health (IDLH).
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Question: Open Circuit
Answer: In an open-circuit SCBA, air is exhaled directly into the ambient atmosphere.
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Question: Closed circuit
Answer: In a closed-circuit SCBA, exhaled air is recycled by removing the carbon dioxide with an alkaline scrubber and by replenishing the consumed oxygen with oxygen from a solid, liquid, or gaseous source.

As required by MSHA/NIOSH 30 CFR Part 11.80, all compressed breathing gas cylinders must meet minimum U.S. Department of Transportation (DOT) requirements for interstate shipment. (For further information, see 49 CFR Part 173 and 178.) All compressed air, compressed oxygen, liquid air, and liquid oxygen used for respiration shall be of high purity and must meet all requirements of OSHA 29 CFR Part 1910.134(d). In addition, breathing air must meet or exceed the requirements of Grade D breathing air as specified in the Compressed Gas Association pamphlet G-7.1 and ANSI Z86.1-1973.
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Question: Deciding the Appropriate Use of SCBA
Answer: Key questions should be asked when considering whether an SCBA is appropriate:
Is the atmosphere IDLH or is it likely to become IDLH? If yes, a positive-pressure SCBA should be used. A positive-pressure SAR with an escape SCBA may also be used.

Is the duration of air supply sufficient for accomplishing the necessary tasks? If no, a larger cylinder should be used, a different respirator should be chosen, and/or the work plan should be modified.

Will the bulk and weight of the SCBA interfere with task performance or cause unnecessary stress? If yes, use of an SAR may be more appropriate if conditions permit.

Will temperature effects compromise respirator effectiveness or cause added stress for the worker? If yes, the work period should be shortened or the mission postponed until the temperature changes.
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Question: Supplied Air Respirators
Answer: Supplied-air respirators, also known as air line respirators, supply oxygen to a face-piece via a supply line from a stationary source. SARs are available in positive-pressure and negative-pressure modes. Pressure-demand SARs with escape provisions provide the highest level of protection (among SARs) and are the only SARs recommended for use at hazardous waste sites.

SARs are NOT recommended for entry into IDLH atmospheres (MSHA/NIOSH 30 CFR Part 11) unless they are equipped with escape SCBAs. The air source for supplied-air respirators should be compressed air cylinders or a compressor that purifies and delivers ambient air to the face-piece. SARs suitable for use with compressed air are classified as "Type C" supplied-air respirators as defined in MSHA/NIOSH 30 CFR Part 11.

All SAR coupling must be incompatible with the outlets of other gas systems used on-site to prevent a worker from connecting to an inappropriate compressed gas source (OSHA 29 CFR 1910.134(d)). SARs enable longer work periods than do SCBAs and are less bulky. However, the air line impairs worker mobility and requires workers to retrace their steps when leaving the area. Also, the air line is vulnerable to puncture from rough or sharp surfaces, chemical permeation, damage from contact with heavy equipment, and obstruction from falling drums, etc.

All such hazards should be removed prior to use. When in use, air lines should be kept as short as possible (300 feet or 90 meters is the longest approved hose length for SARs). Other workers and vehicles should be kept away from the air line.

The use of air compressors as the air source for an SAR at a hazardous waste site is severely limited by the same concern that requires workers to wear respirators; the questionable quality of the ambient air. On-site compressor use is limited by OSHA Standard 29 CFR Part 1910.134(d).
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Question: Deciding the Approiate use of SAR
Answer: Key questions to ask when considering SAR use are:
Is the atmosphere IDLH or likely to become IDLH? If yes, SAR/SCBA combination or SCBA is necessary.
Will the hose significantly impair worker mobility? If yes, the work task should be modified or other respiratory protection should be used.
Is there a danger of the air line being damaged or obstructed (e.g., by heavy equipment, falling drums, rough terrain, or sharp objects) or permeated and/or degraded by chemicals (e.g., by pools of chemicals)? If yes, either the hazard should be removed or another form of respiratory protection should be used.
If a compressor is the air source, is it possible for airborne contaminants to enter the air system? If yes, have the contaminants been identified, and are efficient filters and/or sorbents available that are capable of removing those contaminants? If no, either cylinders should be used as the air source or another form of respiratory protection should be used.
Can other workers and vehicles that might interfere with the air line be kept away from the area? If no, another form of respiratory protection should be used.
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Question: Combination SCBA/SAR
Answer: A relatively new type of respiratory protection is available that uses a regulator to combine the features of a SCBA with a SAR. The user can operate the respirator in the SCBA or SAR mode, through either the manual or automatic switching of air sources. This type of respirator allows entry into and exit from an area using the self-contained air supply, as well as extended work periods within a contaminated area while connected to the air line. It is particularly appropriate for sites where workers must travel an extended distance to a work area within a hot zone and remain within that area for relatively long work periods (e.g., drum sampling). In such situations, workers would enter the site using the SCBA mode, connect to the air line during the work period, and shift back to the SCBA mode to leave the site.

The combination SCBA/SAR should not be confused with a SAR with escape provisions. The primary difference is the length of air time provided by the SCBA. The combination system provides up to 60 minutes of self-contained air, whereas the escape SCBA contains much less air, generally enough for only 5 minutes. NIOSH certification of the combination unit allows up to 20 percent of the available air time to be used during entry, while the SAR with escape provision is certified for escape only.
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Question: Respirator Fit
Answer: A similar reduction in protection can result from low or high ambient temperatures. For example, at very low temperatures, the exhalation valve and regulator can become ice-clogged due to moisture in the breath and air. At high temperatures, excessive sweat can cause a break in the face-to-face-piece seal. A poor face-piece seal can also be associated with the lack of (or improper) fit testing as well as with scars, missing teeth, and facial hair

Facial hair and long hair interfere with respirator fit and worker vision. Any facial hair that passes between the face and the sealing surface of the respirator is prohibited. Even a few days' growth of facial hair will allow excessive contaminant penetration. Long hair must be effectively contained within protective hair coverings.

Eyeglasses with conventional temple pieces (earpiece bars) will interfere with the respirator-to-face seal of a full face-piece. A spectacle kit should be installed in the facemasks of workers requiring vision correction.
When a worker must wear corrective lenses as part of the face-piece, the lenses shall be fitted by qualified individuals to provide good vision, comfort, and a gas-tight seal. Contact lenses can trap contaminants and/or particulates between the lens and the eye, causing irritation, damage, absorption, and an urge to remove the respirator.

Gum and tobacco chewing should be prohibited during respirator use since they can cause ingestion of contaminants and compromise the respirator fit.
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Question: Respirator Fit Testing
Answer: The "fit" or integrity of the face-piece-to-face seal of a respirator affects its performance. A secure fit is important with positive-pressure equipment and is essential to the safe functioning of negative-pressure equipment, such as air-purifying respirators. Most face-pieces fit only a certain percentage of the population; thus, each face-piece must be tested on the potential wearer in order to ensure a tight seal. Recall that facial features such as scars, hollow temples, very prominent cheekbones, deep skin creases, dentures or missing teeth, and the chewing of gum and tobacco can interfere with the respirator-to-face seal. A respirator shall not be worn when such conditions prevent a good seal. A worker's diligence in observing these factors shall be evaluated by periodic checks.
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Question: Qualitative Fit Test
Answer: There are two types of fit tests. The first is a qualitative fit test, which exposes the wearer to irritants (stannic chloride) or substances that have distinctive odors or tastes (banana oil or saccharin mist). If the face-piece fit is good, the wearer should experience no reactions or sensations related to the substance used
The second type of test is the quantitative fit test, which is much more complicated and designed to produce a numerical value, or fit factor, indicating the degree of fit. The wearer is placed in an enclosure containing a known concentration of a contaminant. A sample is taken from inside the face-piece, and the concentration of the contaminant is determined. The airborne concentration is divided by the concentration inside the face-piece to get the fit factor. The new 1910.134 describes fit testing methods in the appendix.
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