CSCS Excavation Safety 2

Question 1

What is the purpose of a Genny (signal generator) used in conjunction with a CAT scanner before excavation?

Accepted Answer

To apply a detectable signal to specific underground services so the CAT can locate non-metallic and dead cables that would otherwise be undetectable

Answer

A Genny (signal generator) connects to or induces a signal onto specific underground services, allowing the CAT to detect cables and pipes that do not naturally emit a detectable signal. This includes dead electrical cables, fibre optic cables, and plastic pipes. HSE guidance HSG47 requires both CAT and Genny to be used together for a thorough survey.

Question 2

What is the recommended safe method for stockpiling excavated material (spoil) adjacent to a trench?

Accepted Answer

Spoil must be kept at least 1 metre from the edge of the excavation and not heaped to a height that could cause instability

Answer

HSE guidance requires excavated spoil to be placed at least 1 metre from the edge of the excavation. Heavy spoil near the edge increases the lateral pressure on the trench sides and significantly increases the risk of collapse. Additionally, loose spoil at the edge can fall into the excavation onto workers below.

Question 3

What action must be taken if water begins to accumulate in an excavation during work?

Accepted Answer

Assess the risk, implement pumping to remove water, check the stability of the excavation sides, and ensure operatives are not at risk of drowning

Answer

Water ingress is a serious risk in excavations — it destabilises the sides, increases the risk of collapse, and creates a drowning hazard. Under CDM Regulations 2015, the competent person must assess the situation, arrange pumping, reinspect the support systems for any deterioration, and ensure workers can safely egress. Work must stop if the risk cannot be controlled.

Question 4

What information must be included in a permit to dig before excavation work commences?

Accepted Answer

The location and extent of the dig, known underground services, CAT/Genny survey results, support methods, emergency contacts, and authorisation signatures

Answer

A permit to dig is a formal document that must include: the exact location and dimensions of the excavation; details of all known underground services from utility plans and CAT/Genny surveys; the proposed method of excavation; support systems to be used; emergency procedures; and authorisation signatures from the competent person and site manager. This is required under CDM Regulations 2015.

Question 5

What is the minimum distance from a known gas main at which mechanical excavation must stop and hand digging must commence?

Accepted Answer

500mm

Answer

HSE guidance HSG47 states that when excavating near known gas mains, mechanical excavation must cease and hand digging must be used when within 500mm of the expected position of the service. This reduces the risk of striking and damaging the gas main. The same 500mm rule applies to other buried services.

CSCS Green Card Practice Test

CSCS Green Card Practice Test

CSCS Excavation Safety 2