Construction Health and Safety
Management
By Dr Simon Smith – licensed under the Creative Commons Attribution – NonCommercial – Share Alike License
http://creativecommons.org/licenses/by-nc-sa/2.5/
Construction Health & Safety Management
Simon Smith (University of Edinburgh)
& Philip Matyear (Balfour Beatty)
Part 9: Excavations
Overview
General
Undermining nearby structures
Legislation
Contact with underground
services
HSE view
Excavations
Access to the excavation
Planning
Suffocating, toxic and explosive
gases
The Hazards of Excavation
Work
Protecting members of the public
Collapse of the sides
Materials falling into
excavations
People and vehicles falling into
excavations
People being struck by plant
Supervision and Inspection
Safe plant - Quick Hitch Buckets
Summary
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
Requires employers and self employed workers
to;
• Ensure they provide and maintain workplaces,
equipment and systems of work that are , so far
as is reasonably practicable , safe to workers
and the public.
• Employees to co-operate and take care of their
own and others health and safety.
Management of Health and Safety at Work
Regs 1999
Requires employers and self employed workers
to;
• Identify the control measures they need to take
when reviewing the hierarchy of control (Reg.
4 ) to produce risk assessments
Construction, Design and Management Regs
1995
Applies to all stages of a construction project and
places duties upon clients, designers and
contractors. The regulations aim to ensure:
• Reduction of risk at the planning and design stages
• Selection of competent appointees and provision of
adequate resources
• Effective management of health and safety
throughout the project
Construction (Health, Safety and Welfare) Regs
1996
Regulation 12 & 13. Excavations, Cofferdams &
Caissons
• Institute safety management systems
• All practicable steps shall be taken, where
necessary to prevent danger to any person from
accidental collapse.
• Appoint competent persons to assist in health
and safety management
• Identify and prevent risk from underground cables
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
above.
Note. This the general principle – Some makes of
box do not rotate at the spindle joint.
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
Protection

Do not store other materials close to the sides of the
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.
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
 Look around for obvious signs of underground
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

of
Provide good ladder access or other safe means
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
Supervision

A ‘competent’ 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 w ork (Excavation) w hich 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
Supervisor
(on behalf of AWG)
Sit e Address:
Inspect ion
Tim e / Dat e
Excavat ion Reference or
Descript ion
Result of Inspect ion
(Brief Sum m ary)
Name / Signature
Act ion Required
Person
undert aking
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 follow ing 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 sometimes with disastrous consequences.
New type of system from
Caterpillar No safety pin
– Integral locking bar
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