The Importance of Respiratory Protection
Wednesday, November 20th, 2019
First, we must understand there are five ways that chemicals enter the body: inhalation (you breathe it in), ingestion, (in your food or drink), absorption (absorbs through the skin), injection (injected into the skin), and ocular absorption (absorbs through the eyes). Inhalation is important because for most chemicals in the form of vapors, gases, mists, or particulates, inhalation is the major route of entry.
Once inhaled, chemicals and/or particulates are either exhaled or deposited in the respiratory tract. If deposited, damage can occur through direct contact with tissue, or the chemical may diffuse into the blood through the lung-blood interface at the alveoli level; where the alveoli tissue is thick enough to hold back the blood but thin enough to allow for oxygen and carbon dioxide to diffuse back and forth. This is called respiration.
Upon contact with tissue in the upper respiratory tract or lungs, chemicals may cause health effects ranging from simple irritation to severe tissue destruction. Substances absorbed into the blood are circulated and distributed to organs that have an affinity for that chemical. Health effects can then occur in the organs, which are sensitive to the toxicant.
Respirators are either air supplied or air purifying. Air supplied can either be an airline respirator (where a mask provides a source of clean breathing air) or a portable tank (typically found in a self-contained breathing apparatus (SCBA)).
If there is a concentration of at least 19.5% oxygen, you can use an air-purifying respirator (APR) that will remove the chemicals and/or particulates. These cartridges are color-coded and can work on either a positive-pressure powered air-purifying respirator (PAPR) or a negative-pressure mechanical air-purifying respirator.
Before you use a respirator in the workplace, OSHA requires you to be medically cleared by a physician or other licensed health care professional. This requires an extensive respiratory history, and OSEA highly recommends a physical examination (chest x-ray and pulmonary function studies), and any other tests recommended by the PLHCP.
Respirators have an assigned protection factor (APF). For example:
- Half mask APR has an APF of 10
- Full-face APR has an APF of 50
- PAPR has an APF of 1,000
- SCBA has an APR of 10,000.
The APF is defined by OSHA as the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program as specified by this section.
Cartridges in APRs and PAPRs have a Maximum Use Concentration (MUC). This is defined by OSHA as the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator. This is determined by the APF of the respirator or class of respirators and the exposure limit of the hazardous substance.
The MUC usually can be determined mathematically by multiplying the assigned protection factor specified for a respirator by the permissible exposure limit (PEL), short term exposure limit, ceiling limit, peak limit, or any other exposure limit used for the hazardous substance.
Now, the $64,000 question for those of us old enough to remember that television show from the 1950s. How do we know the concentration?
The only way to know what respirator to use is to measure the exposure of the chemical and/or particulate. OSHA has assigned PELs to 470 chemicals.
But what chemicals? There are many sources where this information can be found. Technical documentation from chemical suppliers can be researched, but the best ways are the safety data sheet (SDS) and looking at Section 2 for the hazardous constituents
Air sampling, or the science of industrial hygiene, can establish an air sampling strategy to make sure that the concentration has properly researched the possible ceiling, short term exposure limit (STEL) and Action Level (AL), as well as the Immediately Dangerous to Life and Health (IDLH) concentrations. All air sampling is collected from personal samples. These are collected from the breathing zone, a 9-inch invisible radius around the head for an eight-hour work shift. The concentration collected is then converted to a time-weighted average (TWA) exposure to compare to the PEL.
Certain chemicals will need to be collected on specially prepared media for a known time and, if using active sampling (the use of air sampling pumps), a calibrated flow rate needs to be known to establish total volume, and if using passive sampling. The known time must be provided.
Once we know the concentration, we can select the proper respirator that will adequately protect the worker using the assigned protection factor (APF) and the maximum use concentration (MUC).
The wearer can select a respirator and needs to be trained annually on:
- how to don and doff the respirator,
- how to inspect the respirator,
- the limitations of the respirator
- how to perform a positive and negative pressure check each time the respirator is worn.
Once trained, either a qualitative or quantitative respirator fit test must be performed and repeated annually. A qualitative fit test is a yes/no fit to a test agent like saccharin, Bitrex®, isoamyl acetate (banana oil) or irritant smoke. A quantitative fit test fits a probe either into the facemask or cartridge and measures an aerosol concentration inside the mask using a machine called a PortaCount or similar machine.