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The OSHA final rule governing respirable crystalline silica calls for employers to monitor air quality and conduct exposure measurements in some situations.

But how exactly should this monitoring be conducted? How frequently? What should employers do with the results?

In this entry, we’ll try to answer common questions related to this requirement.

Who needs to conduct exposure assessments?

Both construction industry employers and employers in general industry and maritime can potentially be required to conduct exposure assessments if their workplaces expose employees to respirable crystalline silica at or above 25 micrograms — a.k.a. the “action level,” or half of the new PEL. A few specific construction tasks have built-in exceptions.

In construction: The rule says that exposure assessments should be conducted for “all occupational exposures to respirable crystalline silica in construction work, except where employee exposure will remain below 25 micrograms per cubic meter of air (25 μg/m3) as an 8-hour time-weighted average (TWA) under any foreseeable conditions.”

But “employers following the standard for construction need only follow this [exposure assessment] provision, and the remainder of paragraph (d)(2), for tasks not listed in Table 1 or where the employer does not fully and properly implement the engineering controls, work practices, and respiratory protection.”

Table 1 is a list of specific job tasks and corresponding engineering controls that, when followed, limit exposure to respirable crystalline silica.

In general industry and maritime: OSHA says, “The employer shall assess the exposure of each employee who is or may reasonably be expected to be exposed to respirable crystalline silica at or above the action level.”

But then adds:

“Where tasks performed in a general industry or maritime setting are indistinguishable from construction tasks listed on Table 1, OSHA permits employers to comply with either all of the provisions of the standard for general industry and maritime, or all of the provisions of the standard for construction. When this occurs and the employer fully complies with the standard for construction, the employer will not be required to conduct exposure assessments for employees engaged in those tasks.”

So for construction and general industry and maritime alike, the rule says that if you expect an employee could be exposed at a level of 25 micrograms per cubic meter (or greater), you must conduct an exposure assessment in that workspace. The exception is tasks from Table 1 in the construction section of the rule.

Okay, it looks like my employee qualifies for an exposure assessment. What do I do?

OSHA says there are two options — the scheduled monitoring option and the performance option.

Under the scheduled monitoring option: OSHA says the employer can monitor “each employee on the basis of one or more personal breathing zone air samples that reflect the exposures of employees on each shift, for each job classification, in each work area” and re-monitor as needed.

Under the performance option: OSHA says employers can use “any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica,” but “[w]hen using the performance option, the burden is on the employer to demonstrate that the data accurately characterize employee exposure.”

Essentially, under the performance option, the employer is saying, “I don’t need to go in and monitor the air in my employee’s workplace during their work because I already have equivalent data that’s just as accurate.” OSHA makes clear that this equivalent data can be challenged by an OSHA inspector, and it is our estimation that this is probably the riskier option.

Let’s say I go with the scheduled monitoring option.

OSHA provides a pretty straightforward “if/then” guide for how to proceed.

  • Begin by sampling the 8-hour TWA exposure for each shift, job classification, and work area that may be exposed. OSHA says that if “several employees perform the same tasks on the same shift and in the same work area, the employer may sample a representative fraction of these employees in order to meet this requirement.”
  • If the initial monitoring indicates that employee exposure is below the action level — again, 25 micrograms, half of the PEL — then you can stop monitoring that employee. As long as the employee’s work conditions stay the same, you never have to monitor again.
  • If the monitoring indicates that employee exposure is “at or above the action level but at or below the PEL,” you will need to conduct another monitoring within six months.  However, if you can get two consecutive, subsequent readings that show the employee’s exposure level has fallen below the action level, you can stop monitoring that employee, too. (Unless, again, his or her work or work conditions change.)
  • If monitoring indicates employee exposure is above the PEL, you need to conduct another monitoring within three months.

OSHA makes clear that you are required to reassess each employee’s exposure whenever there’s a change in “production, process, control equipment, personnel, or work practices.” However, reassessing doesn’t necessarily equate to re-monitoring. For example, a change in the workplace could eliminate an employee’s chance of being exposed to silica dust entirely, therefore, there wouldn’t be any respirable silica dust emissions to monitor.

Where do I go for information on the technical aspects of the monitoring itself?

Appendix A of the new rule provides all needed technical information about monitoring, and “specifies the procedures for analyzing air samples for respirable crystalline silica, as well as the quality control procedures that employers must ensure that laboratories use when performing an analysis required.”

Do I have to tell my employees the results of their monitoring under the scheduled monitoring option?


OSHA says you have to tell employees within five working days of receiving the results yourself if you’re in construction, and within 15 days if you’re a general industry or maritime employer. OSHA says you can provide the written results individually, or “post the results in an appropriate location accessible to all affected employees.” The key is that the results are in written, not verbal, form.

In addition, OSHA says that when “an exposure assessment indicates that employee exposure is above the PEL,” the written notification must also include information about “corrective action being taken to reduce employee exposure to or below the PEL.”

What if an employee — or a representative, such as a union rep — wants to watch the monitoring process under the scheduled monitoring option?

OSHA says you have to let them. You also have to provide that observer with PPE to wear during the observation (if they need it) free of charge.

However, note that OSHA specifies you don’t have to do this for workers who are not “affected employees.”

So let’s say you have two workers, A and B, at your facility. Only Worker A is exposed to silica dust in his/her work area, and requires monitoring. In this case, you don’t have to let Worker B observe the monitoring process if he/she asks to do so; only Worker A has that right.

What if OSHA conducts its own exposure measurements at my workplace, and those measurements disagree with ones I have previously taken?

In short, it will be up to the inspector regarding how to move forward.

The rule says that “in situations where exposure measurements made by OSHA indicate that exposures are above the PEL, and that result is clearly inconsistent with an employer’s own exposure assessment, OSHA will use its enforcement discretion to determine an appropriate response.”

What if I instead choose the performance option?

OSHA spells out that this approach is “for employers who are able to characterize employee exposures through alternative methods.”

We should note from the outset that this approach:

  • Seems riskier
  • Puts the burden of proof on the employer
  • Provides fewer concrete ways of knowing for certain that you’re covered

OSHA does not provide specifics for exactly what data is acceptable under this option. The rule says “OSHA intends for the performance option to give employers flexibility to accurately characterize exposures using whatever processes or data are most appropriate for their circumstances. The Agency concludes it would be inconsistent to include specifications or criteria in the definition of objective data and thus has not done so here.”

In choosing this option, you are essentially making the case that you can present OSHA with information that will show you have good evidence that you know as much about your employees’ exposure to silica dust as you would under the scheduled monitoring option. OSHA says you can use this option whenever you have “any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica.” Your sources can be previous air monitoring, or simply other information about silica exposure in your facility. However, the key is that this evidence must be as compelling as the results of scheduled monitoring would be.

Is there an example of how OSHA sees the performance option being used successfully?

Sort of.

In the rule, OSHA provides the example of NADA — an automobile dealers’ trade association — which “conducted air monitoring for employees performing a variety of tasks in automobile body shops” and then “worked to ensure that the results of the study were representative of typical operations.” NADA also ensured that “the sampling procedures and techniques for controlling dust were documented.”

OSHA says that therefore, “these data may allow body shops that perform tasks in a manner consistent with that described in the NADA survey to rely on this objective data to characterize employee exposures to respirable crystalline silica.” [Our italics.]

So even in its own example, OSHA will only say that following this model “may” allow NADA body shops to achieve compliance through the performance option. It seems OSHA is hinting that the performance option will always involve greater subjectivity when it comes to whether an employer is compliant or not.

What if the monitoring results or data I use under the performance option were taken a long time ago?

Technically, that’s okay.

In the text of the rule, OSHA says it “has been persuaded [. . .] not to establish time limitations for monitoring results used to assess exposures under the performance option, as long as the employer can demonstrate the data accurately characterize current employee exposures to respirable crystalline silica.”

So, OSHA is saying you can present an inspector with results taken long ago, but it will also be up to you to convince the inspector that the covered employee’s workplace and work has remained substantively unchanged since then.

What if I am using the performance option, and an employee’s work or workplace changes?

In that case, just as under the scheduled monitoring option, you’ll have to reassess whether or not you’re still compliant.

What if want to use the performance option, but I’ll need to see my workers in action before I can be 100% sure their situations are covered by previous data?

In this case, the performance option is probably not appropriate for you.

OSHA says you “must demonstrate that employee exposures have been accurately characterized” for each worker “prior to the time the work commences.”

So you can’t observe your workers working for a while, and then decide if their work is analogous to a previously-monitored situation. You have to be able to make that claim going in.

Whatever option I select, if I conduct exposure measurements, will I need to keep a record of them?


OSHA says employers must “make and maintain an accurate record of all exposure measurements taken to assess employee exposure to respirable crystalline silica.”

OSHA spells out that this record needs to include:

  • “The date of measurement for each sample taken”
  • “The task monitored”
  • “Sampling and analytical methods used”
  • “Number, duration, and results of samples taken”
  • “Identity of the laboratory that performed the analysis”
  • “Type of personal protective equipment, such as respirators, worn by the employees monitored”
  • “Name, social security number, and job classification of all employees represented by the monitoring, indicating which employees were actually monitored”

What if I am using the performance option, and I’m relying on data I didn’t gather myself?

In that case, OSHA says you still have to keep a record of any data you will rely upon to comply with the requirements of the rule.

OSHA specifies this data record must include:

  • “The crystalline silica-containing material in question”
  • “The source of the objective data”
  • “The testing protocol and results of testing”
  • “A description of the process, task, or activity on which the objective data were based”
  • “Other data relevant to the process, task, activity, material, or exposures on which the objective data were based”

What does OSHA say about using an electronic solution to comply with the recordkeeping aspects of this requirement?

In the rule, OSHA makes clear it is very open to the use of an electronic solution for satisfying the exposure measurement and data recordkeeping requirements.

OSHA explicitly notes that “Electronic recordkeeping has become commonplace.” In a case study within the rule concerning a business that must track air monitoring records for hundreds of employees, OSHA says it “understands that there are multiple ways to maintain these records,” and that employers should “use whatever method works best for them, paper or electronic.”

The cloud-based EHS Management Platform from VelocityEHS can provide a central platform from which to manage your EHS responsibilities, and document, track, and report on required information surrounding exposure assessment requirements. You can catalog and analyze employee tasks that qualify them for monitoring, allowing you to better demonstrate compliance, and easily access information related to previous monitorings. In addition, administrative features allow you to quickly and easily notify employees when and where monitoring may be required, and create automatic reminders for when exposure assessments are due to recur. Click here to request a demonstration of these features.