Human Safety, Toxicity, and Personal Protective Equipment
Toxicity is a dose relationship
Acute toxicity is measured by LD50 (dose) or LC50 (concentration). A lower LD50 means a more toxic product. Signal words summarize the most restrictive route of exposure: Danger/Poison for Category I, Warning for Category II, and Caution for Categories III and IV. “Caution” does not mean harmless. Chronic effects, such as cancer or reproductive harm, may appear on the label even when acute toxicity is low.
Exposure routes and PPE
The main routes are dermal, inhalation, oral, and ocular. Labels specify minimum PPE; you may wear more protection, but not less. Common items include coveralls, gloves, boots, eye protection, and respirators. Choose chemical-resistant materials specified by the label, and replace gloves that tear or become contaminated. Fit-test respirators and use the correct cartridge. Remove PPE before eating, drinking, or smoking, and wash thoroughly after work.
Heat and decontamination
New Mexico heat creates a real conflict between PPE and heat illness. Use work-rest cycles, shade, and hydration, but do not strip off required PPE. Plan decontamination before the job: clean water, soap, and a change of clothes. Know first-aid directions on the label and call Poison Control or emergency services when needed.
Traps
Questions often present a product with a low oral toxicity but high dermal toxicity; the signal word reflects the most restrictive route, not just oral LD50. Another trap is assuming gloves are always required or never required-follow the label. Do not mix PPE components from different labels.
Worked example
Product A has an oral LD50 of 50 mg/kg; Product B has 500 mg/kg. Product A is more toxic because a smaller dose can be lethal. If the label requires a respirator for Product A, a dust mask is not an acceptable substitute.