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					School of Engineering and Electronics
                  &
          Bovis Lend Lease




EXCAVATIONS
  Overview

General                        Undermining nearby
                               structures
Legislation
                               Contact with underground
HSE view                       services
Excavations                    Access to the excavation
Planning                       Suffocating, toxic and
The Hazards of Excavation      explosive gases
Work                           Protecting members of the
Collapse of the sides          public
Materials falling into         Supervision and Inspection
excavations                    Safe plant - Quick Hitch
People and vehicles falling    Buckets
into excavations               Summary
People being struck by plant   Further reading
General
Fact - Excavation work is one of the most
hazardous       operations on site.

Fact - If an incident on site is excavation related,
            death or serious injury is the likely
outcome.

Fact - Up to seven people die each year working
in          and around excavations.

Fact - One cubic metre of soil can weigh over
            one tonne ( the same as a new mini car)
Legislation - Principle Requirements
Health and Safety at Work Act etc 1974              Construction, Design and Management Regs
Requires employers and self employed workers         1995
 to;                                                 Applies to all stages of a construction project and
                                                     places duties upon clients, designers and
• Ensure they provide and maintain workplaces,       contractors. The regulations aim to ensure:
  equipment and systems of work that are , so far
  as is reasonably practicable , safe to workers    • Reduction of risk at the planning and design stages
  and the public.                                   • Selection of competent appointees and provision of
• Employees to co-operate and take care of their      adequate resources
  own and others health and safety.                 • Effective management of health and safety
Management of Health and Safety at Work               throughout the project
 Regs 1999                                          Construction (Health, Safety and Welfare) Regs
Requires employers and self employed workers         1996
 to;
                                                     Regulation 12 & 13. Excavations, Cofferdams &
• Identify the control measures they need to take    Caissons
  when reviewing the hierarchy of control (Reg.     • All practicable steps shall be taken, where
  4 ) to produce risk assessments                     necessary to prevent danger to any person from
• Institute safety management systems                 accidental collapse.

• Appoint competent persons to assist in health     • Identify and prevent risk from underground cables
  and safety management                               and services

• Ensure co-ordination and co-operation             • Ensure cofferdams and caissons properly
                                                      designed, constructed and maintained.
• Provide information and relevant information
  training to employees                             • Regulation 29/30 – Inspection and Reporting
                                                      Schedule 7.
HSE view
    Comments by a HSE inspector when the ‘Be Safe and Shore’
guidance notes  were issued in 1999, that are still valid today;
     An HSE spokesperson said:

    "Digging foundations and trenches for drains is one of the first jobs carried
out on    construction sites. For too many workers, it is also the last job they
do.”


   "To most people, being buried alive is the stuff of horror trims, yet every day
    workers either knowingly take that risk or are placed at risk by their
employers.


   "If those managing and supervising such work would stop to consider that
the average cubic metre of soil weighs a tonne - and it is quite common for that
    volume to collapse into an unsupported excavations - they might treat it with
the respect it deserves."
                                THINK BEFORE YOU DIG !
Excavations
No two excavations are the same, they can range from a small hole for a fence
post to a long pipe line project and yet size doesn’t always matter when you
consider the hazards. Here are some typical examples.
Planning
All excavation work must be planned before work commences on site -
This is essential if the work is to be carried out in a safe manner.
 Consider the picture below
                              How much planning has gone into this operation?
                              Would you enter this excavation?
                              Do you think they have considered the following?
                              • Ground conditions and adequate support
                              • Surcharge loads from spoil and mechanical
                                equipment
                              • Existing structures above and below ground
                              • Location of underground services
                              • Ingress of ground / surface water
                              • Access and egress to the excavation
                              • Edge protection and materials falling from height
                              • Protection of the public and others
                              For more information on planning see the
                              Health and Safety Procedures FM-H&S-033 (01).
                              Excavation Checklist No: 1
Excavation – Hazards
1. Collapse of the sides

       Make sure the necessary equipment needed such
as trench sheets, props, baulks, etc are available on site
before     commencing work.
       Prevent the sides and ends from collapsing by
battering them to a safe angle or support with timber,
sheeting or      proprietary support systems
      DO NOT go into unsupported excavations
      Never work ahead of the support
      Remember that even work in shallow trenches can
be     dangerous. You may need       to provide support if
the work involves bending or kneeling within the trench
Excavation – Hazards
1. Collapse of the sides – Correct Installation of Trench
Boxes
                                                                             1. Assemble box with correct
                                                                                spindle assembly to desired
                                                                                trench width
                                                                             2. Excavate ground to about
                                                                                1m or deeper as ground
                                                                                permits and lower box into
                                                                                trench using 4 leg chains of
                                                                                the correct SWL

3. The excavator then progressively
   excavates between the two faces
   of the box plates and pushes
   down on each of the four corners
   of the box using the machine
   bucket.
4. This method continues until the
   desired depth is reached
5. For extension tops the procedure
   is the same.
6. Extraction is the reverse of       Note; This the general principle – Some makes of
                                      box do not rotate at the spindle joint.
   above.
Excavation – Hazards
1. Collapse of the sides – battering back & safe slope
angles




Graph of typical safe slope angles – All angles are from the
horizontal
Extract from – Be safe and shore – HSG 185
Excavation – Hazards
2. Materials falling into excavations – Edge
Protectionstore other materials close to the sides of the
 Do not
      excavations. The spoil may fall into the excavation
and the extra loading will make the sides more prone to
collapse
     Make sure the edges of the excavation are protected
      against    falling materials. Provide toe-boards or
similar.
    Always wear a hard hat when working in excavations
Excavation – Hazards
3. People and vehicles falling into
excavations
 Take steps to prevent people falling into excavations. If
the excavation is 2m or more deep, provide substantial
barriers, e.g Guard rails and toeboards.
 Keep vehicles away from excavations where ever
possible. Use brightly painted baulks or barriers where
necessary
 Where vehicles have to tip materils into excavations,
use stop blocks to prevent them from over running.
Remember      that the sides of the excavatiion may need
extra support
 Excavation – Hazards
 4. People being struck by plant
    Keep the operatives separte from moving plant such as
     excavators and vehicles removing spoil
    Equip vehicles with audible reversing alarms and rear
     visibility aids such as rear view cameras, fish eye and
     convex mirrors.
 Plant operatives should be competent with a card /
certificate to confirm their level of ability such as CTA, CITB,
& the new CPCS.
 Ensure equipment is well maintained and operators
inspect at regular intervals – visual check daily, recorded
every 7 days
Excavation – Hazards
5. Undermining nearby structures

 Make sure the excavaton does not affect the
footings    of scaffolds or the foundations of nearby
structures. Walls       have very shallow foundations
which can be      undermined by even small trenches
 Decide if the structure needs temporary support
before  digging starts. A survey of the foundations
and the advice of a structural engineer may be
needed.
Excavation – Hazards
6. Contact with underground
services around for obvious signs of underground
 Look
services, e.g.   valve covers or patching of footpath and
road surfaces
 Use cable locating devices to track any services and
mark the ground accordingly
 Make sure that the person supervising the
excavation work has service plans and knows how to use
them. Use the ‘permit to dig’ procedure, safe digging
practices and make sure the emergency procedures are
known to every one in the team.
 Correctly support any existing services that encroach
the excavation
Excavation – Hazards
7. Access to the excavation

    Provide good ladder access or other safe means
of   getting in and out of the excavation.
 Ladders must extend 5 rungs / over 1.0m above
topside ground level – same criteria as scaffold
    Tie and secure ladders at all access points
     Install a short ladder on shallow excavations –
       discourage operatives jumping in and climbing
out of       trenches
    Consider the length of excavation and number of
     access points for general and emergency use,
space at regular intervals on long trenches
 Keep access points clear of materials, remove
excess mud etc from ladder rungs as it builds up
Excavation – Hazards
8. Suffocating, Toxic and Explosive Gases.

 When chalk and limestone comes into contact with
acidic      water it can liberate carbon dioxide and
Glauconitic sand (Thanet sand) can oxidise causing oxygen
deficiency.

 Other gases such as methane and hydrogen sulphide
can seep into trenches from contaminated ground or
damaged services (Transco etc).

 Fumes from petrol and diesel engine equipment can
collect within trenches if sited near excavation - this can
lead to asphyxiation and / or poisoning. (Such equipment
should  never be taken into excavations)

    Tests for gas must be carried out before work is started
     and detectors positioned within the working space to
     provide constant monitoring.
Excavation – Hazards
9. Protecting members of the public
 Fence off all excavations in public places to prevent pedestrians
and vehicles falling into them.
 Where children might get onto a site out of hours, take
precautions     (e.g. backfilling or securely covering excavations) to
reduce the chance     of them being injured
    Works on the public highway should be guarded and signed in
     accordance with the New Roads and Street Work Act guidelines
 Excavations close to public thoroughfares need to be well
                                                                             !
signed and   lighted during the hours of darkness
    Keep the operation within the confines of the site boundary         DANGER
                                                                            DEEP
                                                                         EXCAVATION
    Excavations – Supervision and
    Inspection
      A ‘competent’
    Supervision person must supervise the installation, alteration or removal of
         excavation support
        People working in excavations should be given clear instructions on how to work safely.

    Inspection
            a competent person must inspect excavations:
           At the start of each shift before work begins
           After any event likely to have affected the strength or stability of the
    excavation
           After any accidental fall of rock, earth or other material
           A written report should be made after most inspections
           STOP work if the inspection shows the excavation to be unsafe

            Use form (FM-H&S-019 (01) shown on next page to record excavation inspections
Excavations – Inspection Form
With Reference to ‘The construction (Health, Safety and Welfare) Regulations 1996’, the completion of this form constitutes
an Inspection of a place of work (Excavation) which should be completed prior to any access by employees or persons under
control of the employer and regularly thereaft er.

                           EXCAVATION INSPECTION REPORT
                                                       Sit e Saf ety
Sit e Address:                                         Supervisor                           Name / Signature
                                                       (on behalf of AWG)

                                                                                                            Person
  Inspect ion     Excavat ion Reference or              Result of Inspect ion
                                                                                 Act ion Required        undert aking
  Time / Dat e    Descript ion                           (Brief Summary)
                                                                                                          Inspect ion

                                                                                                       Name / Signature


                                                                                                       Name / Signature


                                                                                                       Name / Signature


                                                                                                       Name / Signature


                                                                                                       Name / Signature


                                                                                                       Name / Signature


This report must be ret ained for a minimum period of three months following the completion of the inspection.
‘Quick Hitch’ Buckets
The past has shown that we cannot rely upon the
hydraulic ram located within the quick hitch body to
safely lock and secure the bucket to the lower arm of the
excavator.
Quick hitch systems are now the ‘norm’ on most
excavators and while the locking mechanisms and
technology are improving, buckets still come off -
                                                            New type of system from
sometimes with disastrous consequences.                     Caterpillar No safety pin –
                                                            Integral locking bar
Check the bucket systems on your site and ensure the
safety pin on the older type of system is always in
position and secure.
              Safety pin fits here - Not Here
  Summary

 No excavation can be
      considered safe,
     however shallow !

Always consider the hazards and PLAN the
work.
Use the company procedures and this
presentation as guide to help plan and control
your excavation work.
Further Reading
Available from HSE Books
Consider This !!




Even Grave Diggers use trench
support

				
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