NEBOSH Chemical Hazards 3

Question 1

What is the hazard of carbon monoxide (CO) in the workplace?

Accepted Answer

CO is a colourless, odourless, tasteless gas that binds haemoglobin 200× more strongly than oxygen, causing tissue hypoxia — undetectable without a gas monitor

Answer

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?

Accepted Answer

The minimum concentration of vapour in air required for ignition — below LEL the mixture is too lean to ignite

Answer

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?

Accepted Answer

Carcinogen Category 1A (known human carcinogen) or 1B (presumed) or Category 2 (suspected) — identified by the GHS08 health hazard pictogram

Answer

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?

Accepted Answer

Hydrogen sulphide (H₂S), hydrocarbon gases (methane, propane), drilling muds (chemical additives), NORM (naturally occurring radioactive material), benzene in crude oil, and silica in cuttings

Answer

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?

Accepted 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

Answer

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).

NEBOSH IGC Gulf Practice Test

NEBOSH IGC Gulf Practice Test

NEBOSH Chemical Hazards 3