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About Respiratory Hazards

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Respiratory hazards include harmful substances and below-normal concentrations of oxygen in the air we breathe. What makes a substance harmful depends on its toxicity, chemical state, physical form, concentration, and the period of time one is exposed. Examples include:

  • particulates,
  • gases and vapors, and
  • biological organisms.

Harmful effects are wide ranging and may occur immediately (acute) or take years to develop (chronic).

Examples of Respiratory Hazards

Particulates: These are airborne particles such as dust, fibers, fumes, mists, soot, and smoke. Some are so small they can only be seen with an electron microscope. The diameter of a particulate is usually measured in micrometers (one micrometer equals 1/1,000 millimeter or 1/25,400 inch). Particles with diameters under 10 micrometers are more likely to enter the respiratory system.

Gas and vapors: Gases can spread freely in the air. Vapors are the gaseous states of substances that are liquids or solids at room temperature. Gases and vapors are classified by their chemical forms.

Biological organisms: These include bacteria, viruses, fungi, and other living organisms that can cause respiratory infections.

Oxygen-deficient atmosphere: Normal air has an oxygen concentration of 20.8 percent by volume. When the concentration drops below 19.5 percent, the air is oxygen deficient and considered immediately dangerous to life and health (IDLH). The harmful effects of oxygen deficiency include impaired thinking and coordination, unconsciousness, and death.

Protection from Respiratory Hazards

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Protect yourself and your co-workers from respiratory hazards by doing the following:

  • Identify the respiratory hazards in your workplace.
  • Evaluate employees’ exposures to each hazard.
  • Use the evaluation information to eliminate the hazards or to lower employees’ exposures to safe levels.

This three-step process, summarized below, is called a hazard analysis or hazard evaluation.

Identify the Respiratory Hazards in your Workplace

  • Consider the sources of respiratory hazards such as production processes, work tasks, raw materials, and end products. Each could expose employees to a respiratory hazard. What raw materials are used in a production process? What are the intermediate products and the byproducts of each process? Do employees use equipment or handle substances that could expose them to respiratory hazards?
  • Review safety data sheets (SDS) and chemical inventories to identify chemicals that may expose employees to respiratory hazards.
  • Talk to employees. Do they have safety or health concerns about certain products, materials, or machines? Have they reported signs or symptoms of respiratory conditions?

Evaluate Employees’ Exposures to Each Hazard

Sampling for Exposure - NIOSH
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After you have identified respiratory hazards, evaluate employees’ exposures to determine whether they are exposed to unsafe levels. Evaluate exposures by measuring them or estimate them with data from previous exposure measurements. Three examples:

  • Measure the exposures of individual employees by sampling their breathing air. The procedure – called personal exposure monitoring – is the most accurate way to evaluate exposure levels.
  • Sample the air at specific locations – called area monitoring – to estimate exposures affecting groups of employees. This method is useful when employees move about and may not always be near a hazard’s source.
  • Use representative exposure data from industry studies, trade associations, or product manufacturers to estimate exposures affecting groups of employees. You must be able to show that the data are based on conditions similar to those that exist in your workplace.

Immediately dangerous to life and health (IDLH) refers to an atmospheric concentration of a toxic, corrosive, or asphyxiant substance that poses an immediate threat to life, causes irreversible health effects, or interferes with one’s ability to escape from a dangerous atmosphere. If employees may be exposed to such substances and you are unable to evaluate their exposures, you must consider the exposure immediately dangerous to life and health.

About Exposure Monitoring

Exposure monitoring is the testing of air samples to determine the concentration of contaminants in a work environment. Test data from the samples are averaged over a period of time, usually eight hours, and referred to as a time-weighted average (TWA).

OSHA has established permissible exposure limits (PEL) for specific air contaminates. Exposures must not exceed the eight-hour PEL-TWA in any eight-hour work shift.

Permissible exposure limits are listed in OSHA Standard 1910.1000, Table Z-1 Limits for Air Contaminants, Table Z-2 Toxic and Hazardous Substances, and Table Z-3, Mineral Dusts.

A trained specialist, such as an industrial hygienist, can help you evaluate employee exposures, interpret the results, and suggest how to lower exposures to safe levels.

Controlling Exposure to Respiratory Hazards

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To eliminate or reduce the chance of getting hurt in the workplace, OSHA requires employers to use a prioritized set of hazard control strategies called the Hierarchy of Controls. The highest priority strategies attempt to eliminate, replace or use engineering to manage the hazard, itself. The lower level strategies work to reduce exposure by controlling worker behaviors. Let’s take a look at these strategies.

Elimination and Substitution

If employees are exposed to respiratory hazards at unsafe levels, you’ll need to determine how to protect them from overexposure. You might try to:

  • Completely eliminate the hazard by using another production process or materials that are not hazardous.
  • Substitute or replace a hazardous substance with a less hazardous substance that does not require as much protection.

For instance, when performing abrasive blasting, the worker might replace blasting sand, which contains silica, with abrasive media such as glass beads, corn cob, or air and dry ice.

Engineering Controls

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Water helps to reduce exposure to silica dust.

If you can’t eliminate or replace a respiratory hazard, use engineering controls to lower exposures to safe levels. Such controls “engineer” or physically change the work environment, so the air is safe to breathe. Examples of engineering controls include:

  • isolating a production process so that the employees are not exposed;
  • installing an exhaust hood to remove air contaminants;
  • using wet methods (water) to reduce exposure to airborne dust;
  • integrating dust collection systems into cutting and grinding equipment.

Administrative Controls and Respiratory Protection

Administrative controls establish programs and policies that require employees to use processes, procedures, and practices to help to limit exposure to hazardous substances. As you can see, the primary strategy is to control behaviors to limit exposure. Some examples of administrative controls related to respiratory protection include:

  • requiring employees to use respirators when working with asbestos;
  • conducting hands-on training on the use of respirators;
  • establishing rules for care and maintenance of respirators;
  • mandating medical exams for all employees who will use respirators.

Employees must use respirators for protection from respiratory hazards when engineering controls are not feasible or will not reduce their exposures to safe levels.

Assigned Protection Factor and Maximum Use Concentration

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Assigned Protection Factor (APF) means the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when you implement a continuing, effective respiratory protection program.

For higher-risk exposure situations (i.e., a higher concentration of infectious particles), choosing a respirator with a higher APF provides a higher level of protection for the wearer. The APFs for different types of respirators are presented in Table 1 of the OSHA Respiratory Protection Standard 1910.134. (See table to the right).

Maximum Use Concentration

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Maximum Use Concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator. It is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance.

  • Be sure to select respirators for employees that maintain their exposure to the hazardous substance at or below the MUC.
  • DO NOT apply MUCs to conditions that are immediately dangerous to life or health (IDLH); instead, they must use respirators listed for IDLH conditions discussed later in the course.
  • When the MUC exceeds the IDLH level for a hazardous substance or the performance limits of the cartridge or canister, then set the maximum MUC at that lower limit.

For more information see OSHA Publication 3352, Assigned Protection Factors for the Revised Respiratory Protection Standard.


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Dusts, fibers, fumes, mists, soot, and smoke are all examples of _____.

2. When the concentration of oxygen drops below _____, the air is oxygen deficient and considered immediately dangerous to life and health (IDLH).

3. Which of the following is the most accurate way to evaluate exposure levels?

4. Integrating dust collection systems into cutting and grinding equipment is an example of which hazard control method?

5. Which of the following is defined as the level of respiratory protection that a respirator is expected to provide to employees?

Have a great day!

Important! You will receive an "error" message unless all questions are answered.