NEBOSH Chemical Hazards 3 — Questions and Answers
Question 1: What is the hazard of carbon monoxide (CO) in the workplace?
- CO is a colourless, odourless, tasteless gas that binds haemoglobin 200× more strongly than oxygen, causing tissue hypoxia — undetectable without a gas monitor (Correct answer)
- CO is easily detected by its pungent smell
- CO is only hazardous in confined spaces
- CO causes only mild headaches at all occupational exposure levels
Correct answer: CO is a colourless, odourless, tasteless gas that binds haemoglobin 200× more strongly than oxygen, causing tissue hypoxia — undetectable without a gas monitor
Carbon monoxide is produced by incomplete combustion (diesel engines, gas heaters, welding in confined spaces). Its insidious danger is that it is completely undetectable by human senses until symptoms appear (headache, dizziness, nausea) and rapidly progresses to unconsciousness and death. Continuous monitoring with audible alarms is the only reliable protection.
Question 2: What is the meaning of the 'lower explosive limit' (LEL) for flammable vapours?
- The minimum concentration of vapour in air required for ignition — below LEL the mixture is too lean to ignite (Correct answer)
- The concentration at which vapour becomes toxic
- The maximum vapour concentration that can explode
- The flash point temperature of the liquid
Correct answer: The minimum concentration of vapour in air required for ignition — below LEL the mixture is too lean to ignite
LEL is the minimum vapour concentration (expressed as % of air) that will support ignition. Below LEL, the mixture is too lean (insufficient fuel). Above UEL (upper explosive limit), the mixture is too rich (insufficient oxygen). Between LEL and UEL is the explosive range — all ignition sources must be eliminated.
Question 3: What is the GHS classification for a substance that causes cancer?
- Carcinogen Category 1A (known human carcinogen) or 1B (presumed) or Category 2 (suspected) — identified by the GHS08 health hazard pictogram (Correct answer)
- GHS06 (skull and crossbones)
- GHS02 (flame)
- GHS01 (exploding bomb)
Correct answer: Carcinogen Category 1A (known human carcinogen) or 1B (presumed) or Category 2 (suspected) — identified by the GHS08 health hazard pictogram
GHS classifies carcinogens: Category 1A (known carcinogens with sufficient human evidence — IARC Group 1: asbestos, benzene, formaldehyde), Category 1B (strong presumptive evidence from animal studies), Category 2 (suspected). All identified with the GHS08 health hazard pictogram (exclamation mark silhouette within a circle) and signal word 'Danger' (1A/1B) or 'Warning' (2).
Question 4: What are the specific chemical hazards present in oil and gas drilling operations in the Gulf?
- Hydrogen sulphide (Hâ‚‚S), hydrocarbon gases (methane, propane), drilling muds (chemical additives), NORM (naturally occurring radioactive material), benzene in crude oil, and silica in cuttings (Correct answer)
- Oil and gas operations pose only fire and explosion risks
- Chemical exposure only occurs in refinery operations
- NORM is not a concern in Gulf oil and gas operations
Correct answer: Hydrogen sulphide (Hâ‚‚S), hydrocarbon gases (methane, propane), drilling muds (chemical additives), NORM (naturally occurring radioactive material), benzene in crude oil, and silica in cuttings
Gulf upstream oil and gas workers face: H₂S (toxic, potentially immediately lethal — requires continuous personal monitor), hydrocarbon gases (fire/explosion), benzene (carcinogen in crude), drilling mud chemicals (irritants, potential sensitizers), NORM (naturally occurring radioactive material in scale and produced water), and crystalline silica in drilling cuttings.
Question 5: What personal protective equipment provides the highest level of chemical protection?
- Level A (HAZMAT): fully encapsulating chemical-resistant suit with SCBA — used for unknown or highly toxic/volatile substances where any skin/inhalation exposure must be prevented (Correct answer)
- Level C (air-purifying respirator with chemical-resistant splash suit)
- Standard acid-resistant apron with N95 mask
- Chemical splash goggles and nitrile gloves
Correct answer: Level A (HAZMAT): fully encapsulating chemical-resistant suit with SCBA — used for unknown or highly toxic/volatile substances where any skin/inhalation exposure must be prevented
The US EPA HAZMAT PPE level system: Level A = fully encapsulating vapor-protective suit + SCBA (highest — for unknown atmospheres and highest toxicity/volatility). Level B = chemical-resistant suit + SCBA (high inhalation risk, less severe skin hazard). Level C = air-purifying respirator + splash suit (known contaminant, concentrations within respirator capability). Level D = basic work uniform (no significant chemical hazard).
Question 6: What is 'substitution' as a chemical control measure and what are its limitations?
- Replacing a hazardous substance with a less hazardous one — effective when available, but the substitute must be verified as genuinely less hazardous and technically viable (Correct answer)
- Substitution always eliminates all risk from chemical exposures
- Substitution means replacing all chemicals with water
- Substitution is only applicable in laboratory settings
Correct answer: Replacing a hazardous substance with a less hazardous one — effective when available, but the substitute must be verified as genuinely less hazardous and technically viable
Substitution (e.g., replacing a Class 1A carcinogen with a less hazardous solvent, using water-based instead of solvent-based products) is the second most effective control after elimination. Limitations: a suitable substitute may not exist or may compromise product quality; the substitute may introduce different hazards that must also be assessed; technical constraints may make substitution impractical.
NEBOSH Chemical Hazards 3
What is the hazard of carbon monoxide (CO) in the workplace?