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Blitz Results: Trenching Hazards

Safe At Work Ontario
  • Issued: December 2, 2015
  • Content last reviewed: December 2015

Workers can be seriously injured as a result of hazards involving the construction of trenches.

A trench is an excavation that is deeper than it is wide. Generally, a trench is excavated to install or repair underground utilities such as sewers, electricity, watermains, natural gas and telecommunications and to construct foundations for buildings or other structures.

Trenches can be dangerous due to their depth and relatively narrow opening that can limit escape in an emergency. Workers can also be at risk due to widely varying soil types, unstable ground conditions and high water content.

In July and August 2015, the Ministry of Labour conducted a safety blitz focusing on hazards involving the construction of trenches. They visited construction projects across Ontario where trenches were being excavated.

Construction inspectors checked on compliance with the Occupational Health and Safety Act (OHSA) and its regulations. They checked for safety issues involving:

  • excavation and trenching support systems
  • identification, location and marking of utilities before work is undertaken
  • measures taken to prevent falls by workers and
  • trench work notification to the Ministry of Labour.

The blitz’s goals were to:

  • raise awareness of hazards involving trenches at construction projects
  • increase worksite compliance with the law and
  • prevent injuries that could arise from unsafe work practices.

Report summary

In July and August 2015, ministry inspectors conducted 994 field visits to 862 workplaces and issued 1,683 orders under the OHSA and Regulations for Construction Projects. This included 151 stop work orders. Some of the workplaces were visited more than once.

Of the orders:

  • 21 per cent (345 orders) were issued under the OHSA
  • 77 per cent (1,304 orders) were issued under the Regulations for Construction Projects
  • 2 per cent (34 orders) were issued under other regulations

Of those orders, four frequently issued trench-related orders under the Regulations for Construction Projects involved a failure of employers to ensure:

  • trenches that were four feet or deeper had proper support systems to prevent the walls from collapsing onto workers [Section 234(1)]
  • material, excavated soil and equipment were kept a safe distance from the upper edge of the trench’s wall to prevent the material from falling onto workers and to maintain the wall’s stability [Section 233]
  • workers were wearing personal protective headwear to protect workers in the trench from falling debris [Section 22] and
  • adequate written procedures existed for emergencies and were posted in a conspicuous place at the construction project [Section 17]

Full Report

Inspection blitzes are part of the province’s Safe at Work Ontario compliance strategy. They are announced to the sector by the ministry in advance, although individual workplaces are not identified in advance. Results are posted on the ministry’s website. The blitzes raise awareness of workplace hazards and are intended to promote compliance with the OHSA and its regulations.

Inspectors’ findings may impact the frequency and level of future inspections of individual workplaces. Inspectors may also refer employers to health and safety associations for compliance assistance and health and safety-related training.

Blitz Focus

Inspectors visited construction projects where trenches were being excavated.

In particular, ministry inspectors visited construction projects:

  • with a high incidence of lost-time injuries involving excavation workers
  • where complaints had been received and
  • where there was a history of non-compliance.

Inspectors focused on the following key priorities:

  1. Trench wall support: Inspectors checked that:
    • trenching support systems were in place and excavation walls were properly sloped
    • support systems were designed by a professional engineer if they were prefabricated, hydraulic or engineered systems
    • employers were determining the sites’ soil types to ascertain the strength and stability of excavation walls
    • trench and excavation walls were being stripped of any loose rock or other material that could slide, roll or fall on a worker
    • constructors were taking appropriate precautions to prevent damage to nearby structures, including employing a professional engineer to specify in writing any precautions to be taken
    • there was safe access and egress available to workers
  2. Utilities locations: Inspectors checked that:
    • before beginning work, employers identified, located and marked utilities to prevent worker contact with gas lines, electrical conductors and other services during excavations
    • utility owners were being asked to supervise the uncovering of potentially hazardous utilities if services could not be disconnected during the excavation
  3. Areas adjacent to trenches: Inspectors checked that:
    • a level area extending at least one metre from the upper edge of each trench wall was kept clear of equipment, excavated soil, rock and construction material
    • no equipment, construction material or excavated soil was stockpiled near the upper edge of an excavation wall to ensure debris wouldn’t fall into trenches and onto workers as well as to ensure the excavation wall’s soil wouldn’t collapse
  4. Safety measures: Inspectors checked that:
    • employers had measures and procedures in place to prevent slips, trips and falls hazards
    • a barrier at least 1.1 metres high was provided, when required, at the top of an excavation if it did not meet regulatory slope requirements and was more than 2.4 metres deep
    • a clear work space of at least 450 millimetres was maintained between an excavation wall and any work platform
    • workers were not working alone
  5. Trench work notification: Inspectors checked that:
    • employers were submitting Notices of Project to the Ministry of Labour for trench projects, when required.

Inspection activity summary

Table 1 – Inspection Visits To Construction Projects
Program Activities Number
Field visits 994
Number of workplaces visited 862
Orders issues 1683
Stop work orders 151
Requirements 38
Orders and requirements per workplace visited 1.95
Orders and requirement per visit 1.69

Requirements and stop work orders are part of the total orders issued

Order analysis

Trenching incidents continue to be an issue at Ontario construction projects.

Of the 1,683 total orders issued during the blitz:

Table 2 - Frequently issued orders under Regulations for Construction Projects[1]
Reason for order Number of orders Percentage of total [2] orders
Excavation safety (Sections 222 to 242) 195 11.59%
Registration and notices (Sections 5 to 6) 147 8.73%
Fall protection hazards (Section 26) 143 8.50%
Personal protective equipment (Sections 21 to 25) 123 7.31%
Access and egress to work areas (Sections 70 to 84) 108 6.42%
Emergency procedures (Section 17) 95 5.64%
Housekeeping concerns (Sections 35 to 48) 86 5.11%
Traffic protection (Sections 67 to 69) 75 4.46%
Construction equipment hazards (Sections 93 to 116) 70 4.16%
Fire safety (Sections 52 to 55) 40 2.38%

[1] Contains a sampling of some common order sections
[2] All orders, including those under OHSA and Regulations for Construction Projects

The most frequently issued orders during this blitz were for excavation-related Sections 222 to 242 of the Regulations for Construction Projects. Almost 12 percent of the orders issued during the blitz concerned these sections.

Other frequently issued orders under the Regulations for Construction Projects were related to the excavation work taking place and included the following contraventions:

  • workers not wearing fall protection and not having the fall protection training as required.
  • workers not wearing prescribed personal protective equipment – the most common being hard hats.
  • workers not provided with required access to and egress from work areas located above or below ground level such as stairs, runway, ramp or ladder. This would include access and egress in and out of a trench.
  • no procedures posted at the workplace in case of an emergency.

About 98 per cent of orders in the 2015 trenching blitz were issued to constructors or employers for non compliance with OHSA and the Regulations for Construction Projects.


During the blitz, 345 orders were issued under the OHSA. Of those, 151 (45 per cent) were stop work orders issued in situations where non compliance posed an immediate risk to the health and safety of workers.

The results show that focusing enforcement on the internal responsibility system continues to be a priority for constructors and employers and is a key to workplace health and safety in Ontario.

During a field visit, inspectors continue to encourage and assist all workplace parties, workers, supervisors, employers and constructors, to work together to keep the workplace safe and ensure compliance with the health and safety laws. During the trenching blitz, workplace parties were encouraged to work together to identify and control hazards involving the excavation of trenches.

Next steps

The results of this blitz verify the need to continue focused enforcement activity in the above-noted areas.

Inspectors will continue to focus on trenching hazards that may put workers at risk of injury.

Compliance help for employers

For more information on identifying, preventing and controlling these hazards, please contact Ministry of Labor safety partners.