NEBOSH Chemical Hazards 2 — Questions and Answers
Question 1: What respiratory protection is required when handling materials classified as 'immediately dangerous to life and health' (IDLH)?
- Supplied-air respirator (SCBA — self-contained breathing apparatus or airline respirator) providing independent air supply — not a filter respirator (Correct answer)
- Standard dust mask (FFP2)
- N95 filtering facepiece respirator
- No respiratory protection is required for IDLH concentrations
Correct answer: Supplied-air respirator (SCBA — self-contained breathing apparatus or airline respirator) providing independent air supply — not a filter respirator
IDLH concentrations are those that could cause death, irreversible health effects, or impair escape within 30 minutes. At IDLH levels, the contaminated atmosphere cannot be relied upon at any moment — only supplied-air equipment (SCBA or airline) that provides a completely independent source of breathing air is adequate.
Question 2: What are the properties of a substance that determine its flammability risk?
- Flash point, boiling point, explosive range (LEL–UEL), and vapour density relative to air (Correct answer)
- Colour and odour
- Molecular weight and pH
- Only flash point determines flammability risk
Correct answer: Flash point, boiling point, explosive range (LEL–UEL), and vapour density relative to air
Flash point (lowest temperature at which vapour can ignite): lower flash point = higher flammability risk. Boiling point: lower boiling point = higher vapour generation. LEL/UEL: the range of vapour concentrations that can ignite. Vapour density: vapours heavier than air accumulate in low-lying areas (pits, trenches) creating invisible ignition hazard.
Question 3: What is the difference between 'irritant' and 'corrosive' chemical hazards?
- Irritants cause reversible inflammation at the contact site; corrosives cause irreversible destruction (burns) of living tissue — both are described in the GHS SDS (Correct answer)
- Corrosives are always more dangerous than irritants
- Irritants are only a concern for skin exposure
- There is no practical difference in workplace controls
Correct answer: Irritants cause reversible inflammation at the contact site; corrosives cause irreversible destruction (burns) of living tissue — both are described in the GHS SDS
GHS classification: Skin/eye irritants (categories 2–3) cause reversible inflammatory reaction. Corrosives (category 1) cause irreversible tissue destruction — chemical burns of skin, eyes, and respiratory tract. Severity of harm drives the control requirements. Corrosives require more robust engineering controls and PPE (acid/alkali-resistant gloves, face shield).
Question 4: What is the health significance of 'sensitization' in chemical exposure?
- Once sensitized, even tiny exposures cause severe immune reactions (asthma, contact dermatitis) that worsen with each exposure — sensitized workers must be removed from all further exposure to that substance (Correct answer)
- Sensitization is a minor skin reaction that improves with continued exposure
- Sensitization occurs in all workers exposed to any chemical
- Sensitization can be treated by reducing the exposure level
Correct answer: Once sensitized, even tiny exposures cause severe immune reactions (asthma, contact dermatitis) that worsen with each exposure — sensitized workers must be removed from all further exposure to that substance
Chemical sensitization (to respiratory sensitizers like isocyanates, lab animal proteins, or skin sensitizers like epoxy resins, cobalt) occurs after initial exposure creates immune memory. Subsequent exposures — even at very low levels below OELs — trigger severe immune responses (occupational asthma, contact dermatitis). Sensitized individuals must avoid all further exposure to that allergen.
Question 5: What does 'biological exposure index' (BEI) monitor and how does it complement air monitoring?
- BEI measures chemicals or their metabolites in biological samples (blood, urine) representing internal absorbed dose from all exposure routes — complementing air monitoring which only measures inhalation route (Correct answer)
- BEI replaces air monitoring for all chemicals
- BEI only monitors toxic metals
- BEI is only used in chemical manufacturing
Correct answer: BEI measures chemicals or their metabolites in biological samples (blood, urine) representing internal absorbed dose from all exposure routes — complementing air monitoring which only measures inhalation route
Air monitoring measures only inhalation exposure; BEI (biological monitoring) measures the actual dose absorbed via all routes. For skin-absorbing chemicals (organophosphate pesticides, solvents), air monitoring alone significantly underestimates total exposure. BEIs are set by ACGIH; equivalent biological monitoring guidance values are published by various authorities.
Question 6: What PPE is required when handling concentrated sulphuric acid?
- Chemical-resistant face shield (not just safety glasses), acid-resistant gloves (Neoprene or butyl rubber), chemical-resistant apron or suit, and eye wash station immediately accessible (Correct answer)
- Safety glasses alone are adequate
- Standard nitrile gloves are sufficient
- Normal work clothes are adequate
Correct answer: Chemical-resistant face shield (not just safety glasses), acid-resistant gloves (Neoprene or butyl rubber), chemical-resistant apron or suit, and eye wash station immediately accessible
Concentrated sulphuric acid (highly corrosive, causes severe chemical burns, exothermic reaction with water) requires: face shield (acid splash can cause permanent blindness — safety glasses have gaps), chemical-specific acid-resistant gloves (latex permeates rapidly, nitrile is marginal — neoprene or butyl rubber preferred), chemical-resistant body protection, and immediate access to an eye wash/safety shower.
NEBOSH Chemical Hazards 2
What respiratory protection is required when handling materials classified as 'immediately dangerous to life and health' (IDLH)?