Exposures must be characterized through methods that may include actual measurements of exposure at a worksite, exposure data from industry or a supplier, and calculations of concentration based on amount used (mathematical models).
Data from industry-wide surveys by trade associations may be used as long as they closely resemble the processes and work conditions as described in the survey. The standard does not specify how an employer is to make a reasonable estimate, nor does it require the employer to measure employee exposure (the comprehensive substance-specific health standards have employee exposure monitoring requirements). Even with actual measurements of exposure, some estimation is still involved since monitoring only determines the exposure on a particular day for a specific employee.