Respiratory Protection

 

There are two approaches to respiratory protection. One approach is to ensure that breathing air is of good quality. This is accomplished by supplying air that has the right mixture of oxygen and inert gases and is free of contaminants. An alternate approach is to clean the air before it is inhaled into the lungs. If there are particulates present, it may be possible to filter them from inhaled air. If there are undesired gases, it may be possible to adsorb them or chemically capture them before they are inhaled. The method selected depends on the degree of danger and potential failure of the equipment.

Types of hazards that require respiratory protection are:

 Oxygen deficient atmosphere (An atmosphere with an oxygen content below 19.5% by volume.)

Excessive concentrations of gases and particulates that can interfere with breathing

Certain chemical vapors and particulates that can create acute or chronic health hazards

Many industrial operations generate airborne contaminants. Typical industrial operations that generate airborne hazards include metal casting, grinding, welding, polishing and spray finishing.

OSHA requires different level of respiratory protection for different industrial applications. OSHA requirements for respiratory protection are included in 29CFR1910.134.

Permissible Practice:

The primary means to control occupational diseases caused by breathing contaminated air is through the use of feasible engineering controls, such as enclosures, confinement of operations, ventilation, or substitution of less toxic materials. When effective engineering controls are not feasible, or while they are being instituted, appropriate respirators must be used pursuant to OSHA's Respiratory Protection Standard (29CFR1910.134). Employer must provide respirators, when necessary, which are applicable and suitable for the purpose intended. The employer is responsible for the establishment and maintenance of a respiratory protective program.

Breathing Air Quality:

 Compressed breathing air must meet at least the following requirements:

o        Oxygen content of 19.5 - 23.5%

o        Hydrocarbon (condensed) content of 5 milligrams per cubic meter (mg/m3) of air or less

o        CO content of 10 parts per million (ppm) or less

o        CO2 content of 1,000 ppm or less

o        Lack of noticeable odor

 Compressors supplying breathing air to respirators must be equipped with suitable in-line air-purifying sorbent beds and filters that are maintained and replaced or refurbished per manufacturer’s instructions

 For compressors not oil lubricated, CO levels in the breathing air must not exceed 10 ppm.

 For oil-lubricated compressors, a high-temperature or CO alarm, or both, must be used to monitor CO levels. If only high-temperature alarms are used, the air supply must be monitored at sufficient intervals to prevent CO levels from exceeding 10 ppm.

Respiratory Inlet Covering:

Respiratory inlet covering is the portion of a respirator that forms the protective barrier between the user’s respiratory tract and an air-purifying device or breathing air source, or both. It can be a facepiece, helmet, hood, suit, or a mouthpiece respirator with nose clamp.

Figure 1. Tight fitting coverings

Figure 2. Loose fitting coverings

 

Respiratory Devices:

There are three major classes of respirators :

      1. Air Purifying Respirator (APR)--to remove particulates and gases from inhaled air.
      2. Supplied Air Respirators (SAR)--to provide breathable air from other sources through a supply line.
      3. Self-contained Breathing Apparatus (SCBA)--to supply breathable air through a self-contained source.

Another type of respirator that combines the features of an SAR and SCBA can be added to this list.

      1. Combination (SCBA-SAR) respirators.

People may work in areas that are free of contaminants. However, a leak in a system may produce dangerous breathing atmospheres. In such situations, escape respirators are issued to workers to provide protection for the applicable danger for a very short time. Escape respirators are not intended for general use.

 

Air Purifier Respirators (APR):

This type of respirator has an air-purifying filter, cartridge, or canister that removes specific air contaminants by passing ambient air through the air-purifying element.

Figure 3. Air purifier respirator. 

Contaminants are removed from air by mechanical or chemical means. Prior to inhalation, the ambient air is passed through a mechanical filter, a chemical cartridge or a canister packed with appropriate materials to remove or neutralize the contaminants.

Filter:

A component used in respirators to remove solid or liquid aerosols from the inspired air. Filter is also called air purifying element.

Figure 4. Filters

High Efficiency Particulate Air Filter (HEPA):

This type of filter is at least 99.97% efficient in removing particles of 0.3 micrometers in diameter.

Figure 5. High efficiency particulate air filters (HEPA)

Mechanical filters can remove only a certain type and size particulates from the air. These filters can not remove hazardous gases and vapors from the air.

Cartridge or Canisters:

Cartridge and canisters are containers with a filter, sorbent, or catalyst, or combination of these items, which remove specific contaminants from the air passed through these containers.

Figure 6. Cartridge and canisters.

Respirators that use chemical canisters or cartridges are capable of removing low concentrations of hazardous vapors and gases form the breathing air. The canister and cartridge contain a catalyst or reactant. The catalyst causes a chemical reaction between the chemical vapor and one of the elements that exists in the air, such as oxygen, and converts a hazardous vapor to a less hazardous one. An example of a catalyst used in chemical cartridge respirators is Hapcalite, which enhances the reaction between oxygen and carbon monoxide to produce carbon dioxide:

CO + 1/2 O2 ----> CO2 + Heat

Figure 7. Chemical canister

Chemical canisters are imprinted with an expiration date, after which the canisters must be disposed. Cartridges should be discarded after each use. (Should not be used for longer than one shift or when breakthrough occurs)

Advantages of APR:

Provides high mobility

Lighter weight than self-contained breathing apparatus (SCBA)

 Disadvantages of APR:

Can not be used in IDLH (Immediately dangerous to life and health) atmospheres.

Can not be used in oxygen-deficient atmospheres (Less than 19.5 % oxygen)

Protects only against specific chemicals and up to a specific concentrations.

Requires the monitoring of a contaminant and oxygen levels.

 

Supplied Air Respirator (SAR):

This is an atmosphere-supplying respirator for which the source of breathing air is not designed to be carried by the user. It is also called airline respirator. Air is supplied by a compressor or pump. A mechanical filter is needed to remove the compressor lubricating oil vapors and mists from the breathing air. Hose masks are used in air-line respirators and operated by means of a motor-driven or hand operated blower to make the breathing easier. When a full body suit is used, SAR supplies the air to provide cooling air to the full body suit and hood.

Figure 8. Supply air respirator hose and full body suit.

 

Advantages:

Comfortable to wear

No resistance to inhalation

Disadvantages:

Reduces the mobility, due to the air-line attached to it.

Danger of entanglement

Possibility of hose puncture

 

General characteristics of SAR:

SAR supplies air to a face piece or a full body suit by a supply line from a fixed source. (Do not use pure oxygen).

Available in positive -pressure and negative-pressure modes.

SAR is not recommended for entry into IDLH atmospheres unless the respirator is equipped with an escape bottle, which provides 5 to 15 minutes of emergency air. (SAR-E) (Supplied Air Respirators with escape)

SAR enables longer work periods than do Self contained Breathing Apparatus (SCBA) and are less bulky.

Airline impairs the worker's movement and requires workers to retrace their steps when leaving the area.

Airline is vulnerable to punctures from rough or sharp surfaces, chemical permeation, damage from falling drums.

 

Self-contained Breathing Apparatus (SCBA):

This is an atmosphere-supplying respirator for which the breathing air source is designed to be carried by the user.

Figure 9. Self contained breathing apparatus (SCBA)

 

General Characteristics:

Consists of a face piece connected by a hose and a regulator valve to an air source which can be compressed air, compressed oxygen or oxygen generating chemical, carried by the wearer.

Available in positive or negative pressure modes.

Only positive pressure SCBAs are recommended for entry into atmospheres that are IDLH.

SCBA offers protection against most types and levels of contamination.

Duration of air supply is limited by the amount of air carried and its rate of consumption.

Bulky and heavy.

Increases the possibility of heat stress.

May impair movement in confined spaces.

Used by workers who handle hazardous materials and operate in highly contaminated areas.

SCBA can be used as a combination of SCBA and SAR.

 

Combination SCBA/SAR:

This type of respirator uses a regulator to combine the features of an SCBA with an SAR. User can operate the respirator in either mode by means of a manual or automatic switching mechanism.

Figure 10. Combination SCBA-SAR

Advantages:

Combination SCBA/SARs can be used for:

Long work periods

Long distances between which a worker has to perform a certain task within a contaminated area.

 

Other Self-contained Breathing Apparatus types:

Open-circuit SCBA:

This apparatus does not recover the expired air and requires a large supply of contaminant free air.

Figure 11. Open-circuit SCBA

 Closed-circuit SCBA:

This apparatus recovers oxygen from expired breath to extend the time of use.

Figure 12. Closed-circuit SCBA

 Fit Tests:

Quantitative

Qualitative

Quantitative fit test: This test is used for air-purifying respirators. A chemical agent is injected into the atmosphere and special instruments are used to determine if the agent is leaked into the face piece.

Figure 13. Quantitative fit test equipment.

 Qualitative fit test:

A harmless agent that has an odor or irritating effect is injected into the air inside an enclosure where the test is conducted, The person who wears the respirator is to detect the presence of the agent inside the face piece by using his/her senses.

Before applying the qualitative and quantitative fit tests to detect any leakage, the workers who will use respirator must select the proper respirator that fits the best.

Try at least five different sizes from two or more manufacturers.

Wear at least for 5 minutes before making a decision.

Qualitative fit test must be repeated at least every 6 months, and should be repeated immediately when the worker has a:

Weight change of 20 pounds or more

Significant facial scar

Significant dental changes

Reconstructive or cosmetic surgery

Any other condition such as growing beard, long side burns, that may interfere with the face piece sealing.

 

Reporting requirements: A summary of the test results must be kept on file for 3 years and it should include the name of the employee, date of test, respirators selected.

 

Other fit tests:

Negative pressure test: Close inhalation valve and breathe in. If there is a good fit, the face piece will collapse against the face.

Positive-pressure test: Close exhalation valve and exhale into the face piece. If the face piece bulges, there is no air leak which indicates a good fit.

 

LINKS

 

OSHA ‘s Training on respiratory protection

Frequently Asked Questions about Respirators

 

Back to Table of Contents

 

Last Update: Janury 9, 2007

Prepared by : Serdar Z. Elgun