Advanced Sciences and Mathematics
What the exam expects
This domain tests application, not recall. You must convert units, average exposures over time, and read study results critically.
Toxicology. Know dose-response, routes of entry (inhalation, dermal, ingestion, injection), acute versus chronic effects, latency, target-organ specificity, and how particle size and vapor pressure drive airborne concentration. Odor threshold is not a protective warning property. IDLH guides respirator and escape decisions; it is not an exposure limit.
Physics. Fall protection clearance equals free fall plus deceleration distance plus harness stretch plus a safety margin - a 6-ft lanyard can produce well over 12 ft of total fall. Noise is logarithmic; a 3 dB increase doubles sound energy. Ventilation follows Q = V x A, linking flow, face velocity, and hood area.
Statistics and epidemiology. Separate standard deviation (spread within a sample) from standard error (precision of a mean), and incidence (new cases per population at risk over time) from prevalence (all cases present at a point). Sensitivity, specificity, and predictive value behave very differently when a disease is rare.
Traps that catch candidates
- Converting ppm to mg/m3 incorrectly: mg/m3 = ppm x molecular weight / 24.45 at 25 C and 1 atm.
- Applying an 8-hour TWA limit to a short, high exposure; that is a STEL or ceiling question.
- Confusing OSHA's 5 dB exchange rate with ACGIH's 3 dB rate.
- Treating statistical significance as practical significance.
Worked example
A worker is exposed to 100 ppm solvent for 4 hours and 50 ppm for 4 hours. TWA = (100x4 + 50x4) / 8 = 75 ppm. Compare 75 ppm to the 8-hour limit. If the limit were 50 ppm, the exposure exceeds it even though half the shift was exactly at the limit.