NEBOSH CC Excavation and Demolition Safety

Question 1

Before any excavation work begins on a construction site, what is the essential first step to identify underground hazards?

Accepted Answer

Obtain service plans from utility providers and carry out a CAT and Genny scan of the area

Answer

HSG47 (Avoiding Danger from Underground Services) requires obtaining up-to-date plans from all utility providers and then using a cable avoidance tool (CAT) and signal generator (Genny) to scan the excavation area. Plans alone are insufficient as services may have been diverted or added without updating records.

Question 2

What is the primary purpose of trench support (shoring) during excavation work?

Accepted Answer

To prevent the collapse of trench sides, which could bury workers

Answer

Trench support systems (shoring, trench boxes, sheet piling, battering) prevent the collapse of excavation sides, which is one of the most serious hazards in construction. Unsupported trenches can collapse without warning, burying workers under tonnes of soil. One cubic metre of soil weighs approximately 1.5-2 tonnes.

Question 3

Under what circumstances might battering (sloping the sides) be preferred over vertical shoring for an excavation?

Accepted Answer

When there is sufficient space to slope the sides to a safe angle and the ground conditions are suitable

Answer

Battering involves cutting the excavation sides to a safe angle (typically 45 degrees or less for most soils). It is preferred when there is adequate space, as it avoids the need for support equipment. However, the safe angle depends on soil type, moisture content, and surcharge loads. A competent person must determine the appropriate angle.

Question 4

What hazardous atmosphere might accumulate in a deep excavation, and what precautions are required?

Accepted Answer

Carbon dioxide, methane, or hydrogen sulphide can accumulate; gas monitoring and ventilation are required

Answer

Deep excavations can accumulate hazardous gases including CO2 (from decomposing organic matter), methane (from landfill or natural deposits), and H2S (from sewers or contaminated land). Oxygen depletion can also occur. Gas monitoring before entry, continuous monitoring during work, and provision of ventilation are essential precautions.

Question 5

A building is to be demolished. Under CDM 2015, what specific document must be prepared before demolition work begins?

Accepted Answer

A detailed demolition method statement prepared by a competent person, included within the construction phase plan

Answer

CDM 2015 Regulation 20 requires that demolition or dismantling of a structure is planned and carried out in a safe manner under the supervision of a competent person. A detailed method statement must be prepared, describing the sequence of demolition, structural stability measures, hazardous material removal (especially asbestos), and exclusion zones.

NEBOSH Construction Certificate Practice Test

NEBOSH Construction Certificate Practice Test

NEBOSH CC Excavation and Demolition Safety