CSCS Excavation Safety 3

Question 1

Who is legally defined as the 'competent person' required to inspect excavations under CDM Regulations 2015?

Accepted Answer

A person with sufficient training, experience, and knowledge to identify hazards and specify the necessary precautions for excavation work

Answer

Under CDM Regulations 2015, a competent person is someone with sufficient training, experience, knowledge, and other qualities to carry out the inspection properly. For excavation inspections, they must understand soil mechanics, support systems, and the hazards of excavation work. They must produce written inspection reports that are kept on site.

Question 2

What colour does a CAT scanner display or indicate when it detects a power cable in 'Power' mode?

Accepted Answer

The signal strength increases and an audible warning sounds — the operator must mark the position and determine the depth before any excavation

Answer

In Power mode, the CAT detects the electromagnetic field naturally emitted by live power cables. The signal strength meter shows increasing readings as the detector approaches the cable, and an audible tone becomes louder. The operator must mark the cable's position on the ground and use the Genny to establish its depth. HSE guidance HSG47 requires all modes (Power, Radio, Genny) to be used.

Question 3

What hazard does vibration from nearby plant or traffic pose to an open excavation?

Accepted Answer

Vibration can destabilise the sides of the excavation, increasing the risk of collapse, and may dislodge shoring or trench box supports

Answer

Vibration from heavy plant, traffic, or piling operations can significantly destabilise excavation sides, particularly in granular soils. It can also dislodge shoring supports and cause previously stable soil to collapse. Under CDM Regulations 2015, the competent person must consider vibration sources in the risk assessment and may need to restrict plant movement near excavations.

Question 4

What must happen if an uncharted underground service is discovered during excavation?

Accepted Answer

Stop work immediately, make the area safe, and report the discovery to the site manager who must identify the service before work resumes

Answer

If any unexpected underground service is encountered during excavation, all work must stop immediately. The area must be made safe and the discovery reported to the site manager. The service must be positively identified by contacting the relevant utility provider before any further work takes place. This is required under HSE guidance HSG47 and the CDM Regulations 2015.

Question 5

What is the purpose of monitoring equipment such as inclinometers used on large excavation projects?

Accepted Answer

To detect and measure ground movement around the excavation, providing early warning of potential instability or collapse

Answer

Inclinometers and other monitoring equipment measure lateral ground movement around excavations. They provide early warning of ground displacement that could indicate impending collapse, allowing preventive action before failure occurs. On large or deep excavations, CDM Regulations 2015 may require ongoing monitoring as part of the construction phase plan.

CSCS Green Card Practice Test

CSCS Green Card Practice Test

CSCS Excavation Safety 3