An excavation is a hole left in the ground as the result of removing material. A trench is an excavation in which the depth exceeds the width. Trenching and excavation work is inherently dangerous. Hazards include cave-ins, struck-by injuries, electrical contact, and slips, trips, and falls.
As part of Safe At Work Ontario's strategy to raise awareness of the hazards involved in this type of work, to prevent injuries and illnesses that could arise from unsafe work practices, and to ensure workplace parties are complying with health and safety legislation, the Ministry of Labour (MOL) will be conducting a safety blitz on excavation projects in May 2013.
During the MOL's excavation safety blitz, inspectors will be targeting the following types of excavation projects:
- “trenching” (digging of long narrow excavations) to install or repair services such as natural gas, electrical, telecommunications, and sewers
- construction of foundations
- “soil retention” (stabilizing soil in an excavation)
- digging basements for residential housing
- forming “footing” (supports) for the construction of buildings or bridges
- road construction and repair involving excavation.
One of the biggest hazards related to trenching and excavation is the risk of cave-ins. An unstable trench or excavation can collapse, killing or injuring workers by suffocation or crushing when a worker is buried by falling soil. Trench stability is affected by a number of factors such as:
- improper use or installation of support system or trench box
- soil type and moisture content
- depth of the trench
- length of time the trench is left open
- surcharge (excessive weight near the trench)
- adjacent buildings and structures
- existing foundations, and
- previous excavations or soil disturbances.
There are three basic methods of protecting workers against trench cave-ins:
- trench boxes
Most fatal cave-ins occur on small jobs of short duration such as service connections and excavations for drains and wells. Too often people think that these jobs are not hazardous enough to require safeguards against collapse. Unless the walls are solid rock, never enter a trench deeper than 1.2 metres (4 feet) if it is not properly sloped, shored, or protected by a trench box.
The risk of a cave-in is not the only hazard in trenching. Injuries and deaths are also related to other major areas:
- falls into excavation or trench
- slips, trips, and falls while accessing, egressing, or working in the excavation or trench
- insufficient personal protective equipment
- contact with overhead electrical conductors and underground utilities
- materials handling and housekeeping
- heavy equipment working near the excavation
- traffic control on the site and on public roads
- confined spaces and hazardous atmospheres
- material, equipment, or vehicles falling onto workers in excavations or trenches
- excavation or trench affecting stability of adjacent structures
- storage of excavated material
- voids, underground parking garages, vaults, subways
- flooding/water hazards.
Before excavating, the gas, electrical, and other services in the area must be accurately located and marked. If the service poses a hazard, it must be shut off and disconnected. Over half of all powerline contacts involve buried cable.
For more info, download the Trenching Hazards chapter of our Construction Health and Safety Manual.
Part III (sections 222 to 242) of the Construction Regulation applies to all excavating and trenching operations. It identifies the various types of soils and specifies the type of shoring and timbering to be used for each. It spells out the precautions that must be taken before an excavation is begun and the requirements for trench support systems that must be designed by a professional engineer.
- Trenching Safety (Hazard Introduction)
- Traffic Control – Temporary Work Zones
- Traffic Control and Backing Vehicles
- Confined Space Entry
- Confined Spaces Hazard Awareness for Construction
- Ladder Handling – Hands On
- Electrical Safety – Underground Workers
- Cable Locating
- Personal Protective Equipment
- Pipeline Construction Safety Training (Online)
A reminder to call Ontario One Call or contact the utilities in the area before excavating a site.
Contains everything you need to recognize and protect yourself against construction health and safety hazards. 350 pages. Revised, Apr 2013.
A comprehensive safety manual, similar to Construction Health and Safety Manual (M029), developed for six trades: boilermakers, millwrights, refrigeration and air-conditioning mechanics, pipe trades, sprinkler and fire protection trades, and insulators.
Pocket-sized card showing excavator handsignals. 4¼” x 2¾”. Two-sided.
This advisory outlines what you need to do before clearing a blocked sewer service line.
This DVD covers all major hazards and safeguards involved in trenching operations. The main focus is on preventing and protecting against cave-ins, but it also explains sloping, shoring, and trench boxes in detail. 27 minutes. Colour.
This advisory contains helpful information for the excavator about locating underground utilities before starting to dig. 1 page.
The Safety Talks manual covers a wide variety of safety topics for the construction industry. By presenting the information in a concise and easily digestible format, you can prevent an injury or save a life in just 5 minutes. Revised May, 2008.
The Trenching Safety manual provides an introduction to trenching hazards. Contents include: soil types, causes of cave-ins, protection and safeguards, and emergency procedures. 32 pages. Revised, Nov 2010.
This safety meeting package contains everything you need to conduct a multimedia safety meeting. Conveniently available on CD, this package contains an electronic slideshow presentation on Trenching, facilitator's notes and a quiz on the content of the presentation.
Conducting a five-minute safety talk is hands-on way to remind workers that health and safety are important on the job and can help workers recognize and control hazards.
- Wind turbines (IHSA Magazine, Vol 13, Issue 1)
- MOL Blitz Results 2012 (IHSA Magazine, Vol 13, Issue 1)
- Gas and Sewer Line Conflicts (IHSA Magazine, Vol 13, Issue 1)
Visit the MOL website for more info about the blitz.