This is like asking a computer user if they need a keyboard or a mouse. The answer, of course, is that both are important. Likewise, both qualitative and quantitative exposure assessment techniques are important in determining exposures to potential health hazards in the workplace.
What is the difference between the two assessments? A qualitative assessment often reviews all potential exposures, and “triages” or prioritizes these exposures to those likely to result in significant potential health hazards. A quantitative assessment conducts sampling to measure specific exposures, which are then compared to published occupational exposure limits (OELs), such as those in the table below.
|Permissible Exposure Limits (PELs)||Occupational Safety & Health Administration (OSHA)|
|Threshold Limit Values (TLVs)||American Conference of Governmental Industrial Hygienists (ACGIH)|
|Recommended Exposure Limits (RELs)||National Institute of Occupational Safety & Health (NIOSH)|
In a qualitative analysis, an industrial hygienist reviews the toxicity (inherent danger) of an agent along with the frequency, duration, and extent (degree) of exposure to estimate whether a given exposure scenario is “acceptable” or if it is likely to produce a negative health effect. Questions are asked regarding process flow, procedures, and existing exposure controls. Safety Data Sheets (SDSs) are reviewed. Observations are made of equipment operation and employee work practices; and the impact of process variability and worker performance is considered. Such an assessment may be performed for one specific substance or for the entire spectrum of potential occupational health hazards in a given workplace. Once the qualitative process is complete, sampling can be employed to test hypotheses. It can also be used if the qualitative process did not reveal a clear answer.
Quantitative assessment is the evaluation of employee exposure using largely empirical methods, and is the actual measurement of a chemical, physical, or biological agent using some sort of sampling method. Techniques may include the use of direct-reading instruments like sound level meters or gas detectors that provide instantaneous results. Other techniques include the physical collection of a substance on specialized media which is then submitted to a laboratory for analysis. Examples include air sampling pumps and either sorbent tubes or filter cassettes; mold spore traps; or surface wipe samples.
If sampling results approach or exceed a recognized OEL, exposure controls may be needed. These include engineering controls, administrative controls, and personal protective equipment (PPE). The employer might also substitute the particular agent with a less toxic alternative, or might choose to eliminate the agent altogether.
Because these assessments only represent a snapshot in time, qualitative assessments should be reviewed and updated whenever there are changes to the agents, processes, and/or controls in the workplace. Prudent practice would also include reviewing qualitative assessments on a periodic basis. Quantitative assessments should also be reviewed and updates when there are concerns for changes in exposures.
Together, these two methods – both qualitative and quantitative – help the employer to characterize the likely exposure of each worker or each “similar exposure group” of workers to various workplace health hazards so that the risk of occupational disease may be effectively managed.