Over five million workers in the United States are required to wear respirators, according to OSHA.  Many of those respirators are one part of a breathing air system.  So what is a breathing air system?

A breathing air system provides adequate quality air to workers in industrial settings with poor air quality.  The system includes an air source, a compressor, air distributors, and respirators.   One needs to know the concentration of harmful contaminants when planning a breathing air system.

Your system’s size and complexity for providing clean and safe air to employees depend on many factors, including what the system will be used for and how many workers will use it.  Read on to learn about some of the factors that go into planning a breathing air system.

What is A Breathing Air System?

A breathing air system is designed to protect people working in numerous industrial settings, including painting, sandblasting, welding, chemical clean-up, and pipe and tank cleaning.  If workers could have repeated exposure to air that could damage their lungs, they need to be provided with a system that offers Grade D breathing air.

Such a system requires both compressors to deliver air to the user and a way to purify the air, typically a respirator.  There are three types of breathing systems:

  • Constant flow.  In some systems, a continuous supply of air is sent through the respirator.  This minimizes air leakage and the entry of air contaminants.  
  • Demand flow.  The wearer controls the flow of air to the respirator since air enters the respirator when the user inhales.  A demand flow system is ideal for work done for short durations.   Air is provided by compressed air, either from an air cylinder or an on-line compressor.
  • Pressure-demand.  In a pressure-demand system, airflow is continuous and increases when the user inhales.  Compressed air is used to deliver air, and this system requires a tighter fitting respirator due to the increased pressure.
Image Credit: westernsafety.com

How Do Breathing Air Systems Work?

When breathing air systems are designed, they must include the following components:

Air Source

The work area needs to provide enough air for each employee as measured by CFM (cubic feet per minute), or a portable compressor or individual compressed breathing air cylinders need to be used.

Air compressor

Air compressors and ambient air pumps are used to provide air to the respirators.  They are designed to maintain Grade D air, not to create it.  Keeping any exhaust separate from the air intake is essential.

To determine the compressors’ size, one must multiply the number of workers by the flow rate of the respirators and then add in the air the tools will require and an additional 10% of capacity. 


Oil-lubricated compressors are frequently used for two reasons:

  • can provide air for numerous workers at the same time
  • provide adequate pressure for many cooling devices

However, unless they are used correctly, there is a substantial risk of breathing in carbon monoxide, which is created when oil is heated.  Therefore, the air intake needs to be located away from an oil compressor’s exhaust.  Due to the risk of carbon monoxide poisoning, these systems require a monitoring system for excess carbon monoxide levels.

Ambient Air Pumps

Ambient Air Pumps are a second common air source commonly used to provide air for respirators.  Since ambient air pumps—sometimes called rotary vane pumps—are not powered by oil, there is less danger of carbon monoxide exposure. 

If an air pump is driven by a compressor, the breathing lines are separated from the compressor to ensure there can be no oil contamination.

Ambient Air Pumps With Mask
Ambient Air Pumps With Mask

Air Distribution

The breathing system must include air regulators, pressure gauges, relief valves, and the air lines to distribute air from the pumps to the respirator.


Air-purifying respirators (APRs) use either a filter or adsorption to remove contaminants from the air.  These tight-fitting respirators come in several different forms, including quarter-, half-, and full-facepiece coverings.  An added advantage of full-face piece APRs is they protect a wearer’s eyes from irritating chemical exposure.

Supplied-air respirators (SARs) connect to an air line and supply clean air from an area outside the workspace. 

SARs can be loose- or tight-fitting.  The face piece on a tight-fitting respirator will be half or full.  Loose-fitting SARs can include hoods or helmets that cover the head or loose-fitting face pieces with side shields.

What are the OSHA Requirements for Breathing Air Systems?

OSHA Standard 29 CFR 1910.134 requires employers to provide respirators that meet Grade D breathing air.  The specifications for this grade of air include

  • The content of oxygen needs to be in the 19.5% to 23.5% range.
  • Carbon Monoxide content of 10 parts per million maximum
  • Carbon Dioxide no more than 1,000 parts per million
  • No more than 5 milligrams per cubic meter hydrocarbon content
  • No noticeable odor

OSHA requires that all those specifications be monitored.   OSHA also has requirements for how often equipment should be tested, and those vary greatly.  Most equipment comes with instructions to ensure you follow those guidelines.

Compliance mistakes for respiratory protection are one of the top 5 cited OSHA violations.  Reasons for non-compliance include

  • Lack of a written program
  • Failure to fit and air test
  • Allowing facial hair on tight-fitting face pieces
  • Lack of medical evaluations
  • Not calibrating CO monitors
  • Not keeping good records
  • Using non-approved respirators (or modifying approved respirators)
  • Not using correct filters

Workers who are unsure about compliance matters should consult the employer’s written program.  If there is none, that is a clear violation of OSHA compliance requirements.

What Can Contaminate Breathing Air Systems?

In designing and monitoring a breathing air system, these are the most common contaminants to be concerned about:

Carbon Monoxide

Typically the most common contaminant, CO has no odor or color and is produced when fuel is burned.  CO can enter the airline through the compressor’s air intake or when piston air compressors are overheated.

To keep CO from contaminating breathing air systems, the compressor’s air intake cannot be near any source of carbon monoxide, including engine exhaust.  


Lubricated air compressors sometimes have oil from the pistons enter the air system.  Unlike Carbon Monoxide, oil mist has an unpleasant odor.


  • Moisture from the air enters a compressor, changes to a vapor, and condenses when it is cooled.  Condensation in the helmet or face piece can cause problems for the wearer.  
  • When combined with oil or solids, the resultant sludge can damage components of the system.
  • Rusted pipelines are another concern.
  • If temperatures are low enough, water can freeze and block the flow of air.


Non-lubricating compressors sometimes introduce lubricating materials such as Teflon or carbon into the system. The air intake is another source of solids in a breathing air system.

Breathing Air Systems for Sandblasting

The most significant respiratory risk with sandblasting is silicosis.  This lung disease is caused by dust, which contains silica—a tiny crystal found in sand and rocks.  As silica builds up in the lungs, it can lead to scarring of the lung tissues.  

Some people have acute symptoms—the lungs react within several months and can take action before permanent damage occurs.  But those with chronic or accelerated exposure will not know their lungs have been damaged for a decade or longer.  At that point, the damage is often irreversible.

OSHA lists sandblasting as a source of exposure to silica.  Along with using approved respirators, for sandblasting, the agency recommends using abrasive blasting respirators.   Type CE NIOSH-certified respirators need to cover not only the wearer’s head but neck and shoulder as well.    Air-purifying respirators can be used for cleaning up.  

In addition, sandblasters should wear protective clothing, safety shoes, and hearing protectors.

Breathing Air Systems for Confined Spaces

Confined space breathing systems need to have a clean air supply while allowing the wearer to safely enter and exit.  A self-contained breathing apparatus (SCBA) or supplied-air respirator (SAR) are both acceptable for confined spaces.   

The SCBA has a facepiece, a small compressed air tank, and a regulator valve.  SCBAs come in 30, 45, and 60-minute versions.  

Breathing Air Systems for Emergency Vehicles
Breathing Air Systems for Emergency Vehicles (Source)

Breathing Air Systems for Paint Booths

Paint booths are mainly used to paint cars in body shops, although some artists also use spray booth facilities.   They move air through a workspace and uses an exhaust system to capture and remove dangerous gas vapors.   Booths can use cross drafts or downdrafts to move air.

Due to the contaminants in paint booth air, workers need a breathing air system that keeps them from breathing in these contaminants.  This begins with mechanical ventilation for a spraying area, steel exhaust ducts, ensuring the air will not recirculate into the building.

Filters are another critical part of a paint booth air system.  They ensure that the air that comes into a booth has no contaminants, and the exiting air is free of harmful chemicals.  Regular maintenance of filters is essential.  Dirty filters affect the airflow into the paint booth.  They also introduce dust and overspray, which will require additional buffing, sanding, and cleaning.

Although filters come with recommendations for when they should be changed, those general guidelines might not apply to every paint booth or area.  Manometer or velocity meters are the best way to determine when filters need to be changed.  Consult the filter specs for recommended pressure or velocity differentials. 

Image Credit: airbestpractices.com

Breathing Air Systems for Welding

Poor air quality is considered “the silent hazard” of welding.  Fumes often contain dangerous levels of chromium or zinc.  The filler metal, base metals, and shielding gases all contribute to toxic air.  The International Agency for Research on Cancer has classified welding fumes as a Class 1 carcinogen, which is the same category as smoking.

OSHA recommends employers create systems to ventilate and extract hazardous air and limit a welder’s exposure when those are possible.  Since those are not always possible, OSHA strongly recommends effective respiratory equipment.

Welding equipment manufacturers now offer welding helmets with powered air-purifying respirators (PAPR).  These respirators, such as the B. Helmet PARP Kit, are portable and comfortable enough to ensure that welders will use them correctly.

Mobile Breathing Air Systems

Mobile breathing systems, also known as self-contained breathing apparatus (SCBA) or industrial breathing sets, are devices that provide breathable air to an individual who is in an oxygen-deficient area where the user cannot rely on access to a remote supply of air.   SCBAs are typically used in firefighting, industrial, and medical settings.  

Closed-circuited Breathing Systems

SCBAs can be either closed-circuited or open-circuited.  Closed-circuit mobile breathing systems, also called rebreathers, are used in mine rescues, tunnels, or other areas where the passages are narrow. The user would not be able to navigate the passages with an air tank.

Rebreathers rely on external air.  They extract oxygen from the carbon dioxide that the user exhaled.  This oxygen is then recirculated, and additional oxygen is then added.  Closed-circuited rebreathers differ from open-circuited in that exhaled gas is not directly discharged into the environment.   

Open-circuited Breathing Systems

Open-circuited SCBAs, or industrial breathing sets, rely on filtered, compressed air.  They usually have four components:  

  • A high-pressure tank.  These can be made from aluminum, steel, or a composite.  Because the composites are lighter, fire departments prefer them.  
  • Devices to regulate air pressure.  One regulator reduces the air pressure between the tank and mask.  A second regulator regulates the air entering the mask to standard atmospheric pressure.  
  • A mouthpiece or mask.  Masks may cover the mouth, mouth, and nose, or the entire face.
  • A carrying frame or harness.  

Open-circuited breathing sets release exhaled air directly into the environment and are more common in industrial and firefighting settings.

Breathing masks used in industrial settings that cover the mouth and nose are also called orinasal, oro-nasal, or oral-nasal masks.  An oral-nasal mask can be a stand-alone, independent mask, or connected via a supply nose to a remote gas supply.

Frequently Asked Questions 

Can a Person Have Facial Hair When Being Fitted for a Respirator?

This depends on the type of respirator.  OSHA regulations are clear—helmets and loose-fitting hoods that do not seal against the face can be used with facial hair.

However, a worker cannot have facial hair between the seal and the skin of a tight-fitting respirator.  In other words, the surface where the seal meets the face must be free of facial hair.  This includes disposable respirators.

Do I Have to Wear a Fresh-Air Mask if I am Not Getting Sick?

If you are in an area where you will be exposed to compounds known to cause lung disease, such as isocyanates, you should wear a mask, even if it is hot and uncomfortable.  Just because you are not currently feeling symptoms, the compounds can still cause long-term and irreversible damage to your lungs.  

In Conclusion 

We need air to survive.  In some cases, we know right away that we are not getting enough air, or it is unhealthy.  At other times, however, the damage from breathing polluted air can take months or years to develop. 

By that time, it is too late.  That is why breathing air systems were designed.  Although the OSHA rules can seem overwhelming, they are there to protect the workers and the employers.