Excavations, Confined Spaces, Demolition & Asbestos

A trench 2 metres deep is supported with a trench box and people are working in it. When must a competent person inspect it?

• AAt the start of each shift, and after any event likely to affect stability✓
• BOnce a week, and again after any accidental fall of material from the sides
• CEvery day at midday, and whenever the trench support is extended or altered
• DWhen it is deeper than 1.2 metres, and then at the end of each working shift

Answer: CDM 2015 requires an inspection at the start of every shift before work begins, after any event such as heavy rain or nearby vibration that could affect the sides, and after any accidental fall of rock, earth or material, with a written report where required. Weekly checks or end-of-shift checks leave people working in an unchecked excavation.

Spoil is being stockpiled beside a 1.5 metre deep service trench. As a minimum rule of thumb, how far from the edge should the spoil and any stored materials be kept?

• AAt least 600 mm, the width of a standard trench box panel
• BAt least 1.5 metres, matching the depth of the excavation✓
• CAt least 0.5 metres, so the spoil heap does not obstruct the walkway
• DAt least 3 metres, double the depth of the excavation

Answer: Spoil and materials placed close to the edge load the sides and can cause collapse or fall onto people below, so, although HSE sets no fixed distance, the widely used industry rule of thumb is to keep them back at least the depth of the excavation and never less than 1 metre. Half a metre or 600 mm puts weight right on the crest, while double the depth is more than the accepted rule of thumb demands.

A mechanical excavator is about to break ground close to a marked underground electricity cable. Following HSG47, the site manager should ensure that:

• AThe cable has been confirmed as low voltage so the excavator can dig across it
• BThe utility plans have been printed and pinned in the site office for reference
• CThe excavator is fitted with a toothless bucket and works under a banksman only
• DThe cable has been located with a CAT and genny and is exposed by hand digging✓

Answer: Safe digging means combining plans, a locator survey and careful hand digging with insulated tools or vacuum excavation to expose the service before any machine works nearby. Plans alone are often inaccurate, a toothless bucket and banksman do not prevent a strike, and even low-voltage cables can kill or cause severe burns.

Which of the following is most likely to be a confined space under the Confined Spaces Regulations 1997?

• AA lockable plant room with fixed mechanical ventilation and no gases stored
• BAn open-topped chamber where solvent vapour could collect at an explosive level✓
• CA 1.5 metre deep foundation trench in clean, dry ground with a ladder at each end
• DA fenced roof compound holding gas cylinders in the open air on a windy site

Answer: A confined space is any substantially enclosed place where a specified risk arises, such as fire or explosion, loss of consciousness from fumes or lack of oxygen, drowning, or asphyxiation by free-flowing solids. An open top does not disqualify a chamber if vapour can build up inside it, whereas an ordinary ventilated room, an open compound and a clean dry trench have enclosure or a hazard but not both.

A worker collapses inside a deep manhole during a survey. What should the top person do?

• ARaise the alarm and start the rescue plan without entering the manhole✓
• BClimb down at once to pull the worker out before the gas concentration rises
• CLower a second worker on a rope to fit a mask to the collapsed worker
• DVentilate the manhole for ten minutes and then go down to check breathing

Answer: Most confined-space deaths are would-be rescuers who enter an atmosphere that has already overcome someone, so rescue must follow the pre-planned arrangements using trained rescuers and equipment such as a tripod and winch. Any unplanned entry, whether immediate or after some ventilation, risks adding another casualty.

A site manager is issuing a permit for entry into a live foul sewer chamber. When should the atmosphere be tested?

• ABefore entry and continuously while anyone is inside✓
• BAt the end of the shift so results can be logged on the permit
• CBefore entry only, with a re-test if the work lasts more than 4 hours
• DOnce at the start of the contract by the client's environmental adviser

Answer: Sewer atmospheres change without warning as flows bring in hydrogen sulphide, methane or oxygen-deficient air, so testing must be carried out before entry and then continuously with personal monitors during the work. A single pre-entry reading, a post-shift record or a one-off contract check cannot detect a change that occurs while people are inside.

Under regulation 20 of CDM 2015, the arrangements for demolition or dismantling of a structure must be:

• ARecorded in writing before the work begins✓
• BAgreed verbally with the principal designer
• CReviewed by the HSE at the pre-start meeting
• DFiled with the local authority 28 days ahead

Answer: The regulation requires that arrangements for demolition or dismantling, including how the risk of danger will be controlled, are recorded in writing before the work starts, usually as a method statement supported by a structural survey. A verbal agreement is not a record, and neither the local authority nor the HSE approves demolition methods in advance under CDM.

A demolition contractor proposes pre-weakening a two-storey steel-framed building in the evening, ready for an excavator to pull it down the next morning. What should the site manager insist on in relation to the pre-weakening?

• ASigned confirmation from the client that the building has no remaining occupants
• BA second excavator on standby and a lighting tower in case the work overruns
• CEngineering control of the pre-weakening and an exclusion zone kept up overnight✓
• DA method statement that swaps pre-weakening for hand demolition of the roof

Answer: Pre-weakening deliberately reduces a structure's stability, so it must be designed and supervised by a competent engineer, and the weakened structure must be kept inside an exclusion zone until it is brought down, because it could collapse prematurely at any time. Extra plant and occupancy checks do not address that risk, and hand demolition of the roof would put people onto a structure that is about to be weakened.

Before intrusive refurbishment work begins in an office block built in 1985, which type of asbestos survey is required?

• AA refurbishment and demolition survey✓
• BA structural condition survey of the frame
• CAn asbestos awareness survey by the client
• DA management survey of the occupied areas

Answer: Any building constructed before 2000 may contain asbestos, and work that disturbs the fabric needs a fully intrusive refurbishment and demolition survey to locate materials hidden in voids, ducts and behind finishes. A management survey covers only normal occupation, awareness training is not a survey, and a structural survey looks at load-bearing condition rather than hazardous materials.

During a strip-out, a labourer uncovers a board behind a boiler that looks like asbestos insulating board. What should the site manager do?

• ARemove the board intact and store it in a locked container for later analysis
• BHave the labourer wet the board, bag it and set it aside for a licensed carrier
• CContinue the strip-out with FFP3 masks until the surveyor confirms the material
• DStop the work, keep people away, leave it undisturbed and arrange sampling✓

Answer: Suspected asbestos must not be handled or disturbed by untrained people: the area is cleared and secured, the find is reported, and a competent analyst samples it before any decision on removal. Asbestos insulating board is usually licensable work, so wetting and bagging by a labourer, carrying on with masks, or moving the board all create fibre release and are unlawful.

Which of these asbestos jobs would normally require an HSE-licensed contractor?

• ARemoving asbestos-containing floor tiles with a hand scraper
• BRemoving sprayed asbestos coating from structural steel beams✓
• CRemoving well-bonded asbestos cement sheets from a garage roof
• DRemoving an intact textured coating from a ceiling by hand

Answer: Sprayed coatings, loose lagging and most asbestos insulating board release fibres readily and are licensable work under the Control of Asbestos Regulations 2012. Asbestos cement, textured coatings and floor tiles are generally non-licensed work, though some tasks may be notifiable non-licensed work and still need trained people and controls.

Under regulation 4 of the Control of Asbestos Regulations 2012, the dutyholder for a non-domestic building must:

• ACommission a refurbishment survey every 5 years whatever the use
• BLabel every ACM with the type of fibre and its date of installation
• CFind any asbestos, assess it and keep a written plan to manage it✓
• DRemove all asbestos within 12 months of taking over the premises

Answer: The duty to manage requires the dutyholder to find out whether asbestos is present, assess its condition, keep an up-to-date register and management plan, and pass the information to anyone likely to disturb it. Removal is only necessary where material is damaged or will be disturbed, intrusive surveys are triggered by work rather than a calendar, and fibre-type labelling is not a requirement.