NEBOSH Chemical Hazards 2

Question 1

What respiratory protection is required when handling materials classified as 'immediately dangerous to life and health' (IDLH)?

Accepted Answer

Supplied-air respirator (SCBA — self-contained breathing apparatus or airline respirator) providing independent air supply — not a filter respirator

Answer

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?

Accepted Answer

Flash point, boiling point, explosive range (LEL–UEL), and vapour density relative to air

Answer

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?

Accepted Answer

Irritants cause reversible inflammation at the contact site; corrosives cause irreversible destruction (burns) of living tissue — both are described in the GHS SDS

Answer

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?

Accepted 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

Answer

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?

Accepted 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

Answer

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.

NEBOSH IGC Gulf Practice Test

NEBOSH IGC Gulf Practice Test

NEBOSH Chemical Hazards 2