Actividades

Tunnelling was considered as being inherently dangerous because of the nature of the activities, the variability of the ground and issues arising from working in a confined space which may become dangerous in various ways. Groundworks are likewise inherently dangerous, for similar reasons.

Whilst knowledge and equipment is constantly improving, it is apparent from consultation (and case studies) that high quality risk management is essential at all times. The tunnelling industry in particular has sought to improve communication and activity by fostering closer working between designers and contractors.

The most notable catastrophic event in the UK in recent years was the Heathrow collapse, where massive economic loss was fortunately not accompanied by loss of life.

Those involved in tunnelling and deeper excavations are in general expert in what they do. They are invariably aware of the risks which need to be managed, but the hazards are ever present and have to be taken very seriously.

There have nevertheless been many tunnelling incidents which caused or could have caused a catastrophe. There was a view from the consultees that some of these incidents were due to obvious mistakes, particularly where the risks inherent in the NATM tunnelling method were not rigorously managed.

The UK tunnelling industry appears to work on the issues continuously and insurers take an interest due to the high claims involved and a joint guide has been prepared1.

The management of risk once an activity starts to deviate from the expected has been discussed in the literature2 and the need for Ownership Leadership and Partnership identified (Martin Thurgood, private correspondence). The case studies support the need for rigorous study of potential catastrophic events, independent review (see Glossary), contingency planning, training, avoidance of excessive commercial pressure etc. However, anecdotally procurement still tends often to focus upon risk shedding and lowest apparent cost.

The use of the Observational Method to manage risk in tunnelling and groundworks (as

mentioned in 2.9 above) is a technique in which risks are closely managed on a continuous basis in support of the design and construction strategy (as opposed to being a simple monitoring process, albeit with ‘stop’ limits). Remedial actions are prepared for and then put into play as soon as they are required. The role of the client is central to this.

Compared to the problems of deep excavation, there was a view that temporary works for general excavations and groundworks should pose little difficulty, but unusual situations arise and there is often commercial pressure to leave excavated faced unsupported if they ‘appear’ safe. The consultees felt that potentially catastrophic scenarios can also be posed, as some case studies showed, by issues such as undermining adjacent foundations, if there is inadequate communication, planning and control of the work.

9.2.10 Fire

Fire risks need to be considered in two ways: risk of a fire starting and what happens if a fire does start.

Safety risk assessment for fires will need to include consideration of: § Use of flammable material

§ Potential sources of ignition

§ Risks of rapid fire spread and loss of control § Compartmentation

§ Ease of escape

§ Ease of fire fighting (access, reach etc)

§ Risk to adjacent properties and their inhabitants Fires during construction mainly start from:

§ Vandalism or careless smoking etc § Hot work getting out of control § Electrical fault

Once a fire has started the issues are: § Detection

§ Fire fighting (workers)

§ Escape of workers and others (alarms, escape routes protection) § Reduction of intensity of fire (choice of materials, fire load,

stores/rubbish/waste/housekeeping, fire suppression etc) § Reduction of area of fire

§ Effect upon adjacent properties

§ Release of poisonous gases and particles § Fire fighting (Fire Brigade)

§ Rapid access to reliable information for the fire brigade about hazards, particularly storage of gas cylinders.

1

The joint code of practice for risk management of tunnel works in the UK, 2003, Pub. The British Tunnelling Society

2

Under CDM 2007 (together with, in some aspects of construction, the Regulatory Reform (Fire Safety) Order 2005 or ‘RRO’) these matters should be considered by the Principal Contractor in a Risk Assessment which needs to continuously updated and used as a management tool on site. There was concern from consultees that this is not being done well on some sites.

Fires during construction have in recent decades caused some loss of life and property but in recent years fires on new-build sites using timber frames have experienced a greater level of economic loss and the size and severity of the fires have alerted the industry to the risk of multiple loss of life of fire-fighters, workers and/or others in the building (particularly where there is phased handover) or in adjacent buildings. The consultees felt that dormant sites appear to be particularly at risk but all sites are at some risk, particularly when unattended.

Designers should (under CDM 2007) be considering hazards such as fire, during construction

and in-use and during maintenance, adaptation, refurbishment and demolition. Bearing in mind

the risks during new-build construction referred to above and the risks of fire-spread through breaches in fire protection arising from error or later damage, it is surprising that designers have not (generally) taken steps to eliminate the hazard or to reduce the risks considerably. An appropriate response in some circumstances might be to choose a different form of construction, taking everything into account.

The insurance industry has become increasingly concerned about construction-phase losses in structures using timber framing. Losses during construction can be major because

compartmentation may not yet have been installed and fire fighting systems may be lacking. The causes of fires appear to mainly involve arson, accidents during hot work or smoking.

Arrangements for fire service contact with new projects appear to vary and it has been suggested that it should be an explicit requirement that projects with timber frame construction should be notified to the Fire and Rescue Service.

The response of the contracting and specialist supplier parts of the industry to this catastrophic event risk – which can hardly be a surprise – appears to have been slow. However, the industry has now prepared guidance1 and the HSE is also updating existing guidance2. There is debate about the adequacy of the response as a whole, so far, in the light of fires still being experienced. In particular, designers, specifiers and CDM-coordinators may have been insufficiently involved in managing this safety risk, although the APS (Association for Project Safety) have recently issued guidance3 discussing the issues.

This is an example of an issue which needed to be actively and rapidly addressed.