How should you calculate an Occupational Exposure Limit (OEL) for a chemical with multiple exposure routes?

• A. Take the highest of the route limits.
• B. Use the average of the route limits.
• C. Add all route limits together.
• D. Select the most protective route-based limit (e.g., inhalation) and apply it to the overall exposure.

Answer: (D)

When a chemical can enter the body through multiple routes, you protect against all of them by using the most protective route-specific limit and applying that to the overall exposure. The exposure risk is governed by the strictest boundary among the routes, so selecting the lowest (most protective) route-based limit ensures that no route exceeds what is considered safe. Averaging, summing, or taking the highest route limit could either mask a dangerous route or create an unrealistic overall threshold, potentially leaving some route unprotected. By choosing the most protective limit and applying it to the total exposure, you maintain a conservative and protective standard across all possible entry routes.