Ministry of Labour l Fact Sheet #5 l April 2014

Construction Safety — Excavation Hazards

Hazards involving excavations, including trenches, can kill or seriously injure workers at construction projects.

Cave-insWorkers can be critically injured or die in an excavation cave-in. Many cave-ins occur on small, short-duration jobs like water, gas, electrical and sewer connections. Employers, supervisors and workers must follow the requirements set out in the Occupational Health and Safety Act (OHSA) and Regulations for Construction Projects.

Other hazards falls into trenches or excavations

tripping over equipment

excavated material or other objects falling on workers

exposure to underground services or overhead electrical cables

unstable adjacent structures

mishandled or poorly placed materials

hazardous atmosphere (noxious gases/lack of oxygen)

toxic, irritating or flammable and explosive gases

incidents involving vehicles and other mobile equipment

Plan before you digOBLIGATIONS UNDER THE CONSTRUCTION REGULATIONS

Remove debris and excavated soil near excavation site [s. 223]

Arrange to protect workers from falling into an excavation [s. 233(4)]

Plan for removing water in an excavation [s. 230]

Identify and locate overhead power lines and underground services [s. 228]

Know the types of soil and what sloping, shoring or shielding are required [s. 226]

Prepare an emergency plan [s. 17 - 18]

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REASONABLE PRECAUTIONS UNDER OHSA SECTION 25(2)(H)

Determine how workers will enter and exit an excavation

Know in advance what excavation equipment and tools are needed

Consider possibility of atmospheric hazards (rain) in an excavation

Be aware of nearby vehicles and mobile equipment vibrating the soil

Note environmental conditions

It’s the law!MARK AND LOCATE SERVICES: Employers must ensure all gas, electrical and other services are located or marked in or near the area to be excavated. If a service poses a hazard, it must be shut off and disconnected before the excavation activity begins. If a potentially hazardous service cannot be disconnected, the service owner must be asked to supervise its uncovering during the excavation [Construction Regulation section 228].

ADJACENT STRUCTURES: Constructors must prevent damage to adjacent structures by engaging a professional engineer who must specify in writing the precautions to be taken [Construction Regulation section 229].

SOIL STRENGTH: The soil type will determine the strength and stability of excavation walls. You can determine the soil you have encountered and protect the excavation walls from collapsing by referring to Construction Regulation section 226. Tip: Inspect trenches and excavations following rain, melting snow, thawing earth, and the overflow from nearby streams, storm drains and sewers.

WALL STABILITY: Strip the wall of a trench or excavation of any loose rock or other material that may slide, roll or fall on a worker. [Construction Regulation section 232(1)]. Tip: Keep heavy equipment, excavated soil or rock and construction material away from the edges of the trench or excavation [Construction Regulation section 233].

Keep at least one metre of each wall’s upper edge clear of equipment, excavated soil, rock and construction ma-terial. Do not position or operate a vehicle or machinery in a manner that could affect the wall’s stability [Construc-tion Regulation section 233].

WORK SPACE: Maintain a clear work space of at least 450 millimetres between the wall of an excavation and any formwork, masonry or similar wall [Construction Regulation section 231].

FALL PROTECTION: Provide a barrier at least 1.1 metres high at the top if an excavation does not meet regulatory slope requirements and is more than 2.4 metres deep [Construction Regulation section 233(4)].

PROTECT YOURSELF: Unless walls of a trench are sound and made of solid rock, never enter a trench deeper than 1.2 metres unless it is properly sloped, shored or protected by a trench box. Never work alone in a trench.

PROTECTIVE SYSTEMS: Three basic methods can protect workers against trench or excavation cave-ins and other hazards:

1. Sloping, which involves cutting back the trench wall at an angle inclined away from the excavation.

2. Shoring, which helps support trench and excavation walls to prevent movement of soil, underground utilities, roadways and foundations. Timber and hydraulic systems are the most commonly used supports to shore up walls. Both types must be designed by a professional engineer.

3. Prefabricated support systems (e.g., trench boxes and shields), which can prevent soil cave-ins.

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“COMPETENT PERSON”: Trenches and excavations must be inspected daily for hazards and as conditions change before workers enter them. This must be done by a “competent person” (as defined by the OHSA).

A “competent person”:

has the knowledge, training and experience to organize the work

is familiar with the OHSA and the Construction Regulations, and

can identify existing and potential health and safety hazards and/or unsafe working conditions.

For “unsupported excavations” (excavations that are not trenches and not made of Type 41 soil), a professional engineer must:

provide a written opinion that workers will not be endangered[Construction Regulation section 234(2)(h)], and

inspect the excavation or appoint a competent person to inspect the excavation, as frequently as the opinion specifies [Construction Regulation section. 234(3)].

ENTRY AND EXIT: Excavations require workers to have safe access and egress using ladders, steps, ramps, or other safe means of entering or exiting. Trenches must be provided with ladders. Trench ladders must be placed within the area protected by the support system and be accessible in the event of a collapse [Construction Regulation section 240].

Inspector focusMinistry inspectors check for the excavation and trench hazards identified in this fact sheet. They check that em-ployers, supervisors and workers are complying with the OHSA and its regulations. In particular, they check for compliance with Construction Regulation.sections 222 to 242.

More information Ministry of Labour, construction safety:

www.ontario.ca/ConstructionSafety

Infrastructure Health and Safety Association: www.ihsa.ca/

Workplace Safety and Insurance Board: www.wsib.on.ca

Ontario Sewer and Watermain Contactors Association: www.oswca.org

Operating Engineers Training Institute of Ontario: www.oetio.com

Canadian Safety Association (CSA) standards referenced in occupational health and safety legislation: http://ohsviewaccess.csa.ca/default.asp?lang=EN

1 Type 4 soil: is soft and very loose. It is very sensitive and, upon disturbance, is significantly reduced in natural strength. It runs easily or flows unless it is completely supported before excavating procedures. It has almost no internal strength, is wet or muddy, and exerts substantial fluid pressure on its supporting system.[Construction Regulation section 226 (5)].

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Toll-free numberCall 1-877-202-0008 any time to report critical injuries, fatalities or work refusals. Call 8:30 a.m. to 5 p.m., Mon-day-Friday, for general inquiries about workplace health and safety. Always call 911 in an emergency.

Note: This document does not constitute legal advice. To determine your rights and obligations under the Occu-pational Health and Safety Act (OHSA) and its regulations, please contact your legal counsel or refer to the legislation at www.e-laws.gov.on.ca/html/statutes/english/elaws_statutes_90o01_e.htm .