Get Your Plan in Place to Reevaluate Industrial Hygiene Data

Get Your Plan in Place to Reevaluate Industrial Hygiene Data

Determining when to reassess employee exposures is a challenge that many with industrial hygiene responsibilities face.

You did it! A whole exposure assessment from start to finish. You’ve received the sampling results from the laboratory, notified your employees and submitted a corrective action plan based on the results to your supervisor. You’ve checked it off your list once and for all—but are you done? 

Maybe you’ve found a treasure trove of sampling data: multiple studies over the years, collected by your predecessor, catalogued into tidy exposure groups and archived alongside detailed qualitative assessments. Let it be? Or should you take another look to make sure your employees are as safe as they can be and your company is OSHA compliant?  

You lean back in your desk chair, considering the numbers in front of you, and questions pop up in the back of your mind: is this it? Is this the true picture of the exposures in my facility? What if I need to sample again? How will I know? 

Depending on the hazard you monitored, your reassessment schedule may be dictated by a regulatory schedule. OSHA has sampling frequency requirements for several chemicals, including silica, hexavalent chromium, lead and formaldehyde. For most agents with prescribed schedules, OSHA has the following requirements: 

  • Every three months for exposures greater than the Permissible Exposure Limit 
  • Every six months for exposures between the Action Level and the Permissible Exposure Limit 

But what if you’re looking at exposures outside of OSHA’s limited list of specific standards? How do you decide if you need to reassess? 

Determining when to reassess employee exposures is a challenge that any health and safety professional with industrial hygiene responsibilities faces. Exposure assessments must be updated as the work processes evolve (e.g., operational changes, new equipment is adopted, etc.), materials change and as employees turn over or adapt to new working conditions. Health and safety professionals have the responsibility to decide what conditions trigger a reassessment. 

Quantitative Data 

One of the easiest methods for determining when and what exposures to re-evaluate is to develop a matrix based on your already existing exposure results. The American Industrial Hygiene Association (AIHA) recommends the following matrix in their “A Strategy for Assessing and Managing Occupational Exposures,” 4th Edition: 

Exposure Measurement 


Greater than Exposure Limit 


50-100 percent of Exposure Limit 

Every six months 

25-50 percent of Exposure Limit 

Every nine months 

Less than 25 percent of Exposure Limit 

Every two years 

Periodic monitoring strategies, such as this one, can be used to identify subtle changes in exposures, such as variation between the seasons or as systems undergo routine maintenance or updates. These exposure frequencies may also be adjusted based on properties of a specific agent. For instance, you may choose to monitor exposures to a carcinogen used in your process more frequently, even if exposures are routinely less than 25 percent of the exposure limit you are comparing it to. Or exposures may simply be so infrequent that you choose to evaluate the exposure every time a task occurs, regardless of the results. 

Changes in the Workplace: A Cause for Reevaluation  

Other triggers for reevaluation could be changes to the physical workplace itself. Minor changes to equipment, an increase or decrease in production, or a modification to the process can all result in changes to the exposure profile. Your employee worker population can be a factor; new employees may have greater exposures than more experienced ones based on their work practices. Sometimes an organizational change can influence how your employees interact with the hazard. A significant change to the workday itself, say switching from 8-hour to 12-hour shifts or a period of mandatory overtime, can also have an impact. Even if the exposure measurement itself doesn’t change, you may decide to use a more conservative exposure limit to account for a decrease in recovery time.  

As a result of your previous sampling results, you may have decided to implement some new engineering or work practice controls. Reevaluating exposures once controls are in place can demonstrate if the measures are effective or if more needs to be done to reduce potential exposures. 

You may also choose to reevaluate exposures when existing control systems are modified, or a new system is installed. Additionally, as engineering controls age, they may not be as effective at minimizing exposures, especially in the absence of a preventative maintenance program. Even normal wear and tear to mechanical components in your controls, including fans, ducting or seals, can result in a change to exposures. Repeating exposure monitoring can help determine if there’s been a change in control efficacy. 

Changes to the Hazard 

As processes change and evolve, companies may look to change materials to positively impact performance or profits. Any new materials may have different health effects or may interact with other exposures to change how we consider them. Or a switch to a new vendor leads to a change in the material blend, and the ratio of chemicals is enough to change exposures.  

Changes to our knowledge of the hazards can also have an impact on the exposure profile. New health information is published frequently, and health and safety professionals should stay informed about the hazards associated with the materials in use at their workplace.  

Changes to the body of knowledge may also result in a change to the exposure limit. What may have been acceptable under the previous exposure limit might now be greater than a new limit. For instance, OSHA changed the permissible exposure limit for silica in 2016 and beryllium in 2017, prompting many companies to reevaluate their materials and processes as documented employee exposures exceeded the new limits.  

Periodic Reassessment: It’s a Smart Idea 

Health and safety professionals should plan to periodically review and reassess the entire characterization of an exposure group, starting from the preliminary judgements about exposures and working through the existing data and any changes to the workforce, workplace or the hazards since the previous exposure characterization was established. While the reassessment may simply confirm the existing characterization, it may bring to light an exposure that was previously overlooked or that you decide to revisit because you have more questions. 

If the dataset is large enough, you may decide to use statistics to help determine where you need to collect more data. Some basic statistical tools and graphical presentations can visualize the spread of data, trends over time, or even predict the potential of an unacceptable exposure in an exposure group. The datasets may help you spot variances between seasons or identify issues based on outlying exposures (possibly a chemical release or an employee not following procedure?) or trends (did exposures increase before the maintenance department replaced that fan belt?). 

Determining what exposures to reevaluate and when can be a challenge for health and safety professionals, regardless of their comfort level with industrial hygiene assessments. But you can determine what groups and which exposures need your priority and attention for the future by: 

  1. Knowing your workplace and hazards 
  2. Relying on prescribed schedules 
  3. Using the data already at your fingertips  

Following these strategies will help you stay compliant and keep workers safe. Now all that’s left to do is budget reevaluation assessments!  

This article originally appeared in the May 2022 issue of Occupational Health & Safety.

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