Excavation and trenching literature advises that fatalities have occurred in trenches as shallow as 1.2 metres following a collapse of the excavation sides. The additional risks relating to the excavation of underground services, leaching of dangerous levels of gases from soils and unprotected trenches mean that specific controls must be considered by Silverback and subcontractors while working on site. In relation to excavation work, an adequate system of safety, involving shoring, earth retention equipment or other appropriate measures, is to be provided to control risks to health and safety arising from:
- underground services,
- adjacent buildings, routes or roads that could become unstable as a result of excavation work,
- the collapse of the excavation,
- objects falling into the excavation,
- persons falling into excavations,
- the placement of excavated material, and
- a person inhaling or otherwise being exposed to, carbon monoxide or another impurity of the air.
Means a hole in the earth, or face of earth, formed after rock, sand, soil or other material is removed.
Means an excavation where the maximum depth is more than the minimum width.
Is a system of temporary supports and sheeting material used to maintain the stability of the sides of an excavation.
Means a cable, pipe or other thing laid or installed underground for the transmission, transportation or storage of electricity or a substance.
About an underground service, means the information about the service necessary to safely do excavation work at or near the service, including-
- the location of the service, and
- the type of the service, and
- the depth of the service, and
- for an electrical service – whether the service is or is not live, and
- the restrictions to be followed in doing the work.
Silverback and subcontracted personnel are to comply with the relevant provisions of the following procedural requirements and references. The typical hazards addressed by this procedure include:
- As principal contractor, Silverback will undertake all necessary investigations regarding underground services prior to work commencing on site. That is, Silverback will find out about underground services via contact with Dial Before You Dig Ph: 1100 and on site testing if appropriate.
- Following these investigations, Silverback will ensure that prescribed information relating to all services on site is given to any subcontractor who may be involved in excavation type work during the project. This information is to be in writing and a record is to remain on file at head office.
- Prior to excavation work commencing, planning and relevant measures are to be taken to ensure the stability of nearby buildings, adjoining structures, routes, roads and the edges of excavations, once work commences.
- Wherever practicable, a barricade or hoarding, 900mm high is to be erected to exclude entry to any excavation where the public may be at risk due to its location and accessibility.
- Wherever practicable, a barricade or hoarding, 900mm high is to be erected to exclude entry to trenches of depth 1m or more where other on site personnel may be at risk due to its location and accessibility.
- All excavations and trenches over 1.5 metres in depth, where entry is required, shall either be shored, battered back or benched unless a geo-technical engineer confirms in writing it is stable.
- All excavations and trenches less than 1.5 metres in depth with unstable rock or soil and where access is required shall be shored, battered back or benched.
- Installation and removal of shoring is to take place from outside the trench.
- Non proprietary shoring is to be designed by an engineer and installed by trained personnel only after a competent person has inspected the trench, assessed the shoring and approved the use of the shoring.
- Each bench cut into the side of the excavation or trench must be no higher than it. is wide and step dimensions are to be no greater than 1.5 metres unless a geo-technical engineer has approved a greater height or dimension in writing.
- Battering is to be at an angle of 45° or less to the horizontal and start no higher than 1.5 metres above the bottom of the trench or excavation, unless a geo-technical engineer has approved a greater batter angle in writing.
- All subcontractors involved in excavation and trenching must ensure as a minimum that a Safety Plan/Work Method Statement is prepared for any work involving excavation work greater than 1.5m deep and that it identifies and details controls for excavation collapse, falling objects, falling into the excavation and inhaling or being exposed to impurities in the air
- All subcontractors involved in trenching must ensure that the work is carried out under the direct supervision of a competent person and details of the person are given to Silverback. This competent person is to undertake, as a minimum, daily inspections of trenches and excavations.
- Covers are to be placed on unattended excavations where practicable on site.
- Barricades and signs are to be used at safe distances (eg: 1 metre) from edges to protect unattended excavations that cannot be practicably covered.
- No person is to work in an excavation or trench alone.
- Petrol driven machinery is not to be located in or near excavations and trenches.
- A safe means of access and egress is to be provided into excavations and trenches requiring access. Ladders providing a safe access and egress are to be placed in every 9 metre length of trench where workers are required to work.
- Mobile plant, materials and spoil is to be kept at least 600mm from the sides of a trench or excavation or at distances that ensures they do not endanger a person present below.
QLD Workplace Health and Safety Act 1995, Sections 22, 28-31
QLD Workplace Health and Safety Regulation 1997, Part 17
(Items 1, 2 & to monitor compliance with this procedure) – Construction Supervisor
(Items 3-19 & to ensure safe trenching and excavation practices) – Subcontractors
- A writen record of the underground investigation results are to be maintained on file