Confined Space Training Certificate Atmospheric Hazards and Gas Testing

Question 1

What is the normal oxygen concentration in ambient air, and at what level does it become immediately dangerous in a confined space?

Accepted Answer

21% normal; below 19.5% is dangerous

Answer

23% normal; below 20% is dangerous

Answer

18% normal; below 16% is dangerous

Answer

20% normal; below 17% is dangerous

Question 2

Before entering a confined space, atmospheric monitoring should ideally be carried out:

Accepted Answer

From outside the space before entry, using remote sampling

Answer

Only if workers can smell unusual odours

Answer

Only after the first worker has entered to check conditions

Answer

Once a week as part of routine maintenance

Question 3

Which gas is commonly referred to as the 'silent killer' in confined spaces because it is colourless and odourless?

Accepted Answer

Carbon monoxide

Answer

Hydrogen sulphide

Answer

Chlorine

Answer

Ammonia

Question 4

What does the term 'LEL' stand for in the context of gas monitoring in confined spaces?

Accepted Answer

Lower Explosive Limit

Answer

Low Energy Level

Answer

Least Effective Limit

Answer

Lower Emission Limit

Question 5

When conducting atmospheric monitoring in a confined space, readings should be taken at multiple levels because:

Accepted Answer

Gases have different densities and may stratify — heavier gases sink and lighter gases rise

Answer

Different monitoring instruments are calibrated for different heights

Answer

HSE requires readings at exactly three heights

Answer

It is only necessary if the space is deeper than 5 metres

Question 6

Hydrogen sulphide (H₂S) is particularly dangerous in confined spaces because:

Accepted Answer

It is heavier than air and can quickly paralyse the sense of smell at higher concentrations

Answer

It is lighter than air and always rises to the top of confined spaces

Answer

It can only be produced by chemical reactions, never naturally

Answer

It has a persistent strong odour that increases with concentration