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Exposure Assessment

3M Center for Respiratory Protection

Respiratory Exposure Assessment

As a safety manager, you need to ensure you’re using the right respiratory protection measures and equipment. To do that, you’ll first need to know the types and levels of airborne contaminants in your job site. A thorough and well-documented exposure assessment process will help you:

  • Identify potential health risks to workers.
  • Prioritise those risks so you can tackle the most serious first.
  • Measure exposure levels to see if they’re acceptable or not.
  • Develop a plan to control unacceptable exposure levels.
  • Keep records of exposure for communicating to workers and complying with government regulations.

Getting Started

It’s not always a simple step-by-step process, but breaking the assessment into smaller tasks makes it more manageable.


Basic Characterisation

In this step, gather information about your workplace: information about the chemical and biological agents present, the workers and their assigned roles or tasks, and the controls you already have in place to ensure respiratory safety.

Start by collecting as much data as you can. The Safety Data Sheets provided by the manufacturers are a good source for answering many of the following questions, but you may have to dig deeper as well.

    • What specific chemicals (not trade or in-house names) are present?
    • What physical form are the contaminants: gas, vapor, mist, particulate?
    • What are the warning signs of exposure, like irritation or odor?
    • Could the chemicals have acute effects — short, immediate effects, usually with high-exposure situations?
    • Could they have chronic effects from lower exposure, with symptoms that may not appear immediately?
    • What are the tasks, routine and otherwise, that generate contaminants?
    • Is inhalation one of the ways your workers could potentially be exposed to the hazard?
    • What are the acceptable exposure levels? Consult Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits, American Conference of Governmental Industrial Hygienists Threshold Limit Values® and manufacturers’ suggested occupational exposure limits.


Similar Exposure Groups

It’s not usually practical to measure every worker’s exposure, so you can assess your workforce by determining similar exposure groups (SEGs). If a group of employees perform similar tasks at the same frequency, using similar materials and methods, they can be considered an SEG. You only need to measure exposure for one of each group.

SEGs can be grouped by:

  • Task and contaminant
  • Task, process and contaminant
  • Task, process, job classification and contaminant
  • Work teams

If you have past exposure monitoring data, it can help you determine SEGs, too.

  • Workforce

    How is your workforce organised? List tasks, who’s assigned to them, how your staff is organised (by team, department, etc.), and the number of people assigned to each task or group.


Qualitative Assessment and Prioritisation

Once you’ve gathered data on workers or SEGs, each person or group’s potential exposure should be ranked. This will help prioritise the most serious risks so you can monitor them first.

Prioritisation should be based on two measurements:

1. Workers’ or SEGs’ potential for exposureto each chemical present in the workplace. Rank from 1 to 4, with 1 meaning typical exposure is expected to be less than 10% of the exposure limit for that agent, and 4 meaning typical exposure is expected to be greater than the exposure limit. You can base your determination on:

  • Past monitoring results at your workplace.
  • Published data about similar situations.
  • Exposure modeling using mathematical models.

2. The health effects of overexposure to the contaminant. Using the toxicity data gathered during basic characterization, rank health effects from 1 to 4, with 1 meaning minimal adverse health effects and 4 meaning life-threatening or disabling.

Prior Matrix


Exposure Monitoring

Monitoring enables you to identify any unacceptable exposures. There are three reasons for exposure monitoring:

  • Baseline — to determine the current level and range of exposures.
  • Diagnostic — to identify specific sources of the contaminants so you can develop control methods, such as making engineering changes or providing respirators.
  • Compliance — to meet regulatory requirements for a specific agent that has more stringent rules, such as asbestos or lead.

How many samples to take depends on your objective. Professional judgment should be used in all cases, plus:

  • For baseline monitoring, you could rely on statistical methods (typically 3 to 10 random samples).
  • For compliance monitoring, follow the OSHA regulations for that contaminant.
  • OSHA calls personal monitoring the “gold standard” for determining employee exposure. Personal samples are collected by attaching a monitor directly to the worker. How long you need to monitor to collect each sample depends on the chemical’s occupational exposure limit and what you’re trying to achieve. For example, you could take:

    • Full shift or 8-hour time-weighted average (TWA) samples.
    • Task-based samples — taking samples for the duration of a specific task (like grinding concrete).
    • 15-minute short-term exposure limits (STEL) or ceiling samples to determine peak exposure levels.

    Samples can be collected on-site and analysed in a laboratory, or in some cases with direct reading instruments. In most cases, the contaminant must be identified in advance, so you can use monitoring equipment and procedures specific to it.

    Any laboratory used should be accredited by the AIHA (link below). Consult the laboratory in advance for preferred sample collection means, shipping requirements, turnaround time for results and cost.


Interpretation and Decision-Making

The criteria for evaluating exposure assessment results should be determined by a safety/health professional prior to exposure monitoring. Once you collect all the necessary data, it must be evaluated to determine whether the exposures are acceptable or not:

  • Acceptable exposures mean you don’t need to take any action.
  • For unacceptable exposures, you’ll need to decide what action is required to manage the exposure, such as installing engineering controls and/or introducing respiratory protection equipment.
  • If there’s insufficient data to make a decision, you’ll need to conduct more assessments and reevaluate.



  • Each time you conduct an exposure assessment, make sure there are detailed records of it, including:

    • A summary of what was done.
    • The purpose of the monitoring.
    • Basic characterization results: task or work group and process descriptions.
    • Explanation of SEG groupings.
    • Exposure criteria selected — TLV or PEL — and why.
    • Results tables of qualitative assessment and prioritization.
    • Health effects of overexposure to the contaminants, including copies of safety data sheets.
    • Monitoring and analytical method used.
    • The conclusions drawn from the data — whether levels are acceptable or not.

    Recommended changes:

    • Changes to try to control the exposure
    • Respiratory protection equipment
    • Future assessment schedule
    • Any other references used during the process.

    Like all parts of your respiratory safety program, exposure assessment is an ongoing responsibility. Even when exposure levels are acceptable, you’ll need to re-evaluate periodically and anytime a new procedure, chemical or workplace change is introduced.


See the next step in your journey to optimising your respiratory protection program.

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