Confined Space Training Certificate Confined Space Definition & Hazards 2

Question 1

What level of hydrogen sulphide (H2S) in ppm is considered immediately dangerous to life and health (IDLH)?

Accepted Answer

100 ppm

Answer

The IDLH level for hydrogen sulphide is 100 ppm. At this concentration, rapid loss of consciousness and death can occur within minutes. H2S is particularly dangerous because it deadens the sense of smell at moderate concentrations.

Question 2

Why is methane particularly dangerous in confined spaces beyond its toxicity?

Accepted Answer

It is highly flammable and explosive in air concentrations of 5–15%

Answer

Methane (CH4) is flammable in concentrations of 5–15% in air (its Lower and Upper Explosive Limits). A single spark can ignite the mixture causing an explosion. It is also an asphyxiant in high concentrations.

Question 3

Which confined space hazard involves the gradual displacement of oxygen by an inert gas?

Accepted Answer

Simple asphyxiation

Answer

Simple asphyxiation occurs when an inert gas such as nitrogen, argon, or carbon dioxide displaces oxygen, reducing its concentration below safe levels. There is no toxic effect from the gas itself — the danger is purely from oxygen depletion.

Question 4

What is the Upper Explosive Limit (UEL) and why is it relevant to confined space safety?

Accepted Answer

The highest gas concentration at which ignition can occur; above this the mixture is too rich to ignite

Answer

The UEL is the highest concentration of a flammable gas in air at which ignition can occur. Above the UEL the mixture is too fuel-rich to burn. The danger zone is between the Lower Explosive Limit (LEL) and UEL.

Question 5

Which physiological effect makes carbon monoxide especially dangerous in confined spaces?

Accepted Answer

It binds to haemoglobin 200 times more readily than oxygen, preventing oxygen transport

Answer

Carbon monoxide (CO) binds to haemoglobin to form carboxyhaemoglobin with an affinity approximately 200–240 times greater than oxygen. This prevents blood from carrying oxygen to tissues, causing cellular hypoxia even when oxygen levels in the air are normal.

Confined Space Practice Test

Confined Space Practice Test

Confined Space Training Certificate Confined Space Definition & Hazards 2