Trenching and Excavating

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Trenching and excavating is dangerous work. Common hazards include:

  • Cave-ins;
  • Falling materials;
  • Being struck by moving equipment;
  • Falls from height;
  • Slips, trips and falls;
  • Electrical shock;
  • Drowning; and
  • Exposure to toxic and flammable gases.

The most important way to prevent injury, illness and death is to plan before you dig. Plan how the excavation will be dug and how it will be maintained to eliminate or reduce hazards. Some risk factors to consider include:

  • Soil type;
  • Weather conditions;
  • Sloping and shoring;
  • Heavy equipment;
  • Vehicle and pedestrian traffic;
  • Utilities (above, below, and nearby); and
  • Water (infiltration, saturation, and water table levels).

Employer Responsibilities

Employers must:

  • Conduct a risk assessment to determine if there is a need to rescue workers, or evacuate them from the excavation site. Develop written procedures for evacuation or rescue, if the risk assessment shows it is necessary. Assign a worker to coordinate those procedures.
  • Locate all utility lines and services before beginning an excavation. Never allow workers to use pointed tools to probe for underground gas or electrical services. Contact the utility owner to confirm the locations of utility lines and services, and to determine how to safely shut off and disconnect.
  • Mark utility locations accurately and inform workers of the locations.
  • Make sure that any drilling or excavation work to be done in proximity to underground services is done in accordance with the instructions of the owner of the service. For instance, they may require that the service is shut off and disconnected before beginning to dig.
  • Prohibit workers from using powered tools or equipment in a manner that could cause damage to utility lines and services.
  • Install guardrails or barriers to prevent workers from falling in to excavations, except at borrow pits.
  • Make sure all walkways entering an excavation more than 1.22 metres deep are:
    • Not less than 50.80 centimetres wide;
    • Equipped with guardrails, if they are more than 1.22 metres above grade; and
    • Provided with cleats when the grade is greater than 1/6.
  • Make sure workers do not enter any place where there is danger of becoming trapped without a means of escape. Provide a ladder if workers are entering an excavation more than 1.22 metres deep. The ladder must extend from the bottom of the excavation to at least 0.91 metres above the top of the excavation edge. Where this is not practical, workers must wear retrieval equipment that is attended at all times by another worker capable of immediately performing rescue.
  • Erect barricades in areas where excavated materials may be dumped, dropped or spilled. Put up warning signs to prevent workers from entering the area without proper instruction or planning.
  • Prevent water from accumulating in the excavation.
  • Secure or remove all trees, boulders or other material that may shift or move within 1.83 metres of the excavation before starting to dig.
  • Prevent workers from entering an excavation more 1.22 metres deep unless the sides of the excavation are sloped to a safe angle, or they are secured with sheet piling, shoring and bracing, or a trench box. If this is not done, workers may only enter if they are protected by another effective way.
  • Consider any added loads in the design of a support system where:
    • Equipment or other heavy objects are close to, or operated near, the edge of an excavation;
    • The excavation is next to or abutting a structure like a building; or
    • The vibrations from nearby equipment or passing vehicle traffic create hazards.
  • Excavate in short sections, and shore or brace any building walls where there is a danger of undermining nearby foundations.
  • Equip a runway used by mobile equipment with curbs in an excavation more than 1.22 metres deep.
  • Prohibit excavated material from being placed within 1.22 metres of a trench or within 1.52 metres of a pit-type excavation.
  • Install vertical planking to protect horizontal shoring members from becoming dislodged when using skips or buckets to remove material.
  • Remove any overhanging banks and trees or stumps within five metres of the excavation’s edge where work is to be done in the excavation.
  • Prevent the erosion of the slope by surface water while work is being done near or in the excavation.
  • Make sure that slopes are scaled and trimmed or otherwise stabilized to prevent slides of material or falls of rock while work is being done near or in the excavation site.
  • Make sure workers use a personal fall protection system when scaling, sloping or trimming banks or faces.
  • Make sure work is done from the top down when scaling or doing similar work. Keep the areas where the resulting debris will fall clear of workers or equipment.
  • Follow standard engineering practices when performing underground work not associated with mineral exploration or extraction, appropriate to the type of work being performed and in accordance with any additional requirements of OHS Division.
  • Gain the approval of OHS Division for methods or equipment that are new, or do not comply with standard practices in underground workings. 
  • Submit to the OHS Division the proposed methods and equipment, as well as evidence of the engineering feasibility with respect to the safety of the workers. 

Where concrete is being installed inside a trench, the employer must:

  • Remove or guard the protruding end of reinforcing steel, such as rebar, that could be hazardous to a worker.
  • Restrict workers from entering areas underneath formwork where placement of a load or a concrete pour is being performed, unless it can be ensured that the formwork can withstand the load.
  • Restrict workers from entering areas underneath formwork where a load or concrete has been placed until it is known that the formwork can withstand the load.
  • Stop the placement of a load or pouring of concrete if the formwork is found to be weak, there is too much settlement, or distortion. Restart operations only after the formwork has been repaired or strengthened, as instructed by a professional engineer.
  • Not apply a load to an unsecured concrete structure, unless it is a part of the erection drawings and supplementary instructions.

Worker Responsibilities

Workers must:

  • Take reasonable care to protect his or her health and safety and that of workers and persons at or near the workplace.
  • Properly wear or use personal protective equipment (PPE), safeguards and safety devices provided for their protection in accordance with the manufacturer’s instructions and training provided by the employer.
  • Follow safe work practices and procedures.
  • Participate in training and hazard assessments, if provided.
  • Not use equipment or perform work tasks where the required training has not yet taken place.
  • Immediately report concerns and hazards to the supervisor or employer.

Related topics

Trenching

Often grouped together, trenches are actually a type of excavation that is defined as less than 3.7 metres wide at the bottom, more than 1.2 metres deep, and of any length.

Excavating

An excavation is defined as “a cut, cavity, trench or depression in the earth's surface resulting from rock or soil removal”.

Soil type

When a soil type is defined, the purpose is to try to identify or predict the potential for the soil to move and cause a collapse while the work is being done.
The soil type is determined by the characteristics of the soil’s consistency, ease of removal, appearance, ability to excavate with hand tools versus machine, water seepage, whether the soil has been excavated before, etc.
In the province, soil types have not been defined; however, the follow general definitions can be used:
  • Good Soil is the most stable soil, it is hard and solid. Examples include clay type soils and glacial till. Such soil cannot be classified as good soil if it is fissured, has been previously disturbed, has water seeping through it, or if it is subject to vibration from sources such as heavy traffic or pile drivers. This soil type is hard to dig by hand, frequently needing the use of a pick. Some authorities call this soil type “A”.
  • Fair Soil is somewhat cohesive, but likely to crack or crumble as it does not stick together well. Examples of this soil type include average soil, angular gravel, silt, and soils that are fissured. This soil type is stiff, but a pick will easily penetrate it. Good Soil types will be considered Fair Soil if it is near sources of heavy traffic or pile drivers. Some authorities call this soil type “B”.
  • Poor Soil is the least stable type of soil, it can be described as soft, sandy and/or loose, and includes granular soils which don't stick together. Examples include gravel and sand. Some authorities call this soil type “C”. (Note: soils with water seeping through it and water saturated soils, muddy soil and wet boggy material are automatically classified as Poor Soil)

Sloping

A method of protecting employees from cave-ins by cutting back the trench wall at an angle that is inclined away from the work area of the excavation. The angle of slope required depends on the soil conditions.

Shoring

A method of protecting employees from cave-ins that supports the sides or walls. Shoring requires installing aluminum, steel, or wood panels that are supported by screws or hydraulic jacks. Some systems can be installed without the workers entering the trench. This option provides additional safety for those workers.

Wherever possible, install the shoring equipment as the excavation proceeds. If there is any delay between digging and shoring, no one should enter the unprotected trench.

Risk assessment

A risk assessment is a thorough check of the work environment and task before work begins.
The purpose is to identify potential hazards and appropriate safety measures to be used to eliminate or reduce the hazards.

Guardrails

A system of vertical and horizontal members that warns of a fall hazard and reduces the risk of a fall.

Cleats

In this context, cleats are strips of material, usually wood, attached across the width of a plank or crawlboard to provide footing. They are typically used on sloped surfaces.

Trench box

A trench box consists of a rectangular structure made of pre-constructed side sheets and adjustable cross members. It is usually made of steel or aluminum.
Trench boxes can be used to protect workers from cave-ins. They can also be used to support or shore the sides of a trench when designed, manufactured and used in accordance with a professional engineer, and when verifying documentation is available.

Workers should not be present in a trench box, when it is moved.

Fall protection system

A fall protection system will either prevent a fall (fall restraint), or bring the worker to a safer stop after falling (fall arrest). Fall restraint methods can vary widely from guardrails and temporary flooring to travel restraint systems. Fall arrest, on the other hand, consists of either a personal fall arrest system or safety net.

Formwork

The foundation, supporting structure, and mould into which concrete may be placed

Personal protective equipment

Any equipment or device which protects a worker's body from injury, illness or death. PPE acts as a barrier to protect the worker from the hazard.
PPE should only be used:
  • Where other controls are not available or adequate.
  • As a short-term measure before controls are implemented.
  • During activities such as maintenance, clean up, and repair where other controls are not feasible or effective.
  • During emergency situations.

OCCUPATIONAL HEALTH AND SAFETY ACT
R.S.N.L. 1990, c. O-3

Section 6 Workers' general duty

6. A worker, while at work, shall take reasonable care to protect his or her own health and safety and that of workers and other persons at or near the workplace.

Section 7 Specific duties of workers

7. A worker

(a) shall co-operate with his or her employer and with other workers in the workplace to protect

(i) his or her own health and safety,

(ii) the health and safety of other workers engaged in the work of the employer,

(iii) the health and safety of other workers or persons not engaged in the work of the employer but present at or near the workplace;

(a.1) shall use devices and equipment provided for his or her protection in accordance with the instructions for use and training provided with respect to the devices and equipment;

(b) shall consult and co-operate with the occupational health and safety committee, the worker health and safety representative or the workplace health and safety designate at the workplace; and

(c) shall co-operate with a person exercising a duty imposed by this Act or regulations.

[S.N.L. 1999, c. 28, s. 3; 2001, c. 10, s. 26; 2004, c. 52, s. 2]

Occupational Health and Safety Regulations, 2012
N.L.R. 5/12

Part III GENERAL DUTIES

Section 17 General duties of workers

17. (1) A worker shall make proper use of all necessary safeguards, protective clothing, safety devices, lifting devices or aids, and appliances

(a) designated and provided for his or her protection by the employer; or

(b) required under these regulations to be used or worn by a worker.

(2) A worker shall follow the safe work procedure in which he or she has been instructed.

(3) A worker shall immediately report a hazardous work condition that may come to his or her attention to the employer or supervisor.

Part V GENERAL HEALTH AND SAFETY REQUIREMENTS

Section 38 Emergency plan risk assessment

38. (1) An employer shall conduct a risk assessment in a workplace in which a need to rescue or evacuate workers may arise.

(2) Where the risk assessment required by subsection (1) shows a need for evacuation or rescue, appropriate written procedures shall be developed and implemented and a worker assigned to coordinate their implementation.

(3) Written rescue and evacuation procedures are required for but not limited to

(a) work at high angles;

(b) work in confined spaces or where there is a risk of entrapment;

(c) work with hazardous substances;

(d) underground work;

(e) work in close proximity to power lines;

(f) work on or over water; and

(g) workplaces where there are persons who require physical assistance to be moved.

(4) Where a workplace is a low risk workplace in the opinion of an employer, the employer shall post information about escape routes and conduct emergency drills he or she considers appropriate.

Part X FALL PROTECTION

Section 138 Definitions

138. In this Part

(a) "anchorage point" means a secure point of attachment for a lifeline or lanyard;

(b) "arborist" means a worker trained and employed, in whole or in part, to climb trees for an economic or scientific purpose, including

(i) detection and treatment of disease, infections or infestations,

(ii) pruning, spraying or trimming,

(iii) repairing damaged trees,

(iv) assessing growth or harvesting potential, or

(v) scientific research;

(c) "body belt" means a belt worn by a worker as a means of fall restraint;

(d) "debris net" means a net that is used to catch material and debris that can drop from work areas;

(e) "fall arrest system" means a system of physical components attached to a worker that stops a worker during a fall;

(f) "full body harness" means a harness consisting of leg and shoulder straps and an upper back suspension unit that distributes and reduces the impact force of a fall;

(g) "guardrail" means a system of vertical and horizontal members that warns of a fall hazard and reduces the risk of a fall;

(h) "lanyard" means a flexible line used to secure a worker to a lifeline, a static line or a fixed anchor point;

(i) "lifeline" means a vertical line attached to a fixed anchor point or a static line and to which a lanyard and a ropegrab may be attached;

(j) "means of fall protection" means a fall protection system and includes a harness, net, rope, body belt, structure or other equipment or device or means of

(i) restraining a worker who is at risk of falling, or

(ii) stopping a worker who has fallen;

(k) "personnel safety net" means a net that is used to catch a worker during a fall;

(l) "ropegrab" means a mechanical fall-arrest device that

(i) is attached to a lifeline and a lanyard, and

(ii) locks itself immediately on the lifeline in the event of a fall;

(m) "safe surface" means a surface at a workplace that

(i) has sufficient size and strength to adequately support a worker who falls on to the surface, and

(ii) is sufficiently horizontal to prevent a further fall from the surface by a worker who has fallen on to the surface;

(n) "softener" means padding or hoses that are used with a lifeline or static line to prevent a rope from being cut or chafed; and

(o) "static line" or "horizontal life line" means a rope

(i) that is attached horizontally to 2 or more fixed anchor points, and

(ii) to which a fall arrest system is attached.

Part XVII CONSTRUCTION, EXCAVATION AND DEMOLITION

Section 376 Definitions

376. In this Part

(a) "adjacent to an excavation" means within a distance less than or equal to the overall depth of the excavation measured from a vertical line through the toe of the excavation face;

(b) "construction project" means erection, alteration, repair, dismantling, demolition, structural or routine maintenance, painting, land clearing, earth moving, grading, excavating, trenching, boring, drilling, blasting, concreting, installation of machinery or other work considered to be construction by the minister;

(c) "demolition" means the tearing down, destruction, breakup, razing or removal of the whole or part of a building or structure, or of free-standing machinery or equipment that is directly related to the function of the structure;

(d) "falsework" means structural supports and the necessary bracing required for the support of temporary load during construction;

(e) "formwork" includes the foundation, supporting structure, and mould into which concrete may be placed;

(f) "tilt-up construction" means a system of building construction in which concrete wall panels are placed in position in the permanent structure and temporarily braced or supported; and

(g) "trench" means an excavation less than 3.7 metres wide at the bottom, more than 1.2 metres deep, and of any length.

Section 384 Concrete placing hazards

384. (1) A protruding end of reinforcing steel that is hazardous to a worker shall be removed or effectively guarded.

(2) Where a worker is required to be underneath the formwork during a concrete pour or placement of another significant load, the worker shall be restricted from the areas where the loads are placed.

(3) A worker shall be restricted from the area under a portion of formwork where a load or concrete has been placed until it can be ensured that the formwork can withstand the load.

(4) Placement of concrete or other loads shall cease in the event of weakness, undue settlement or excess distortion of formwork and may only restart after the formwork has been repaired or strengthened as specified by a professional engineer.

(5) A load shall not be applied to an uncured concrete structure except where permitted by the erection drawings and supplementary instructions.

Section 396 Underground utilities

396. (1) Before excavating or drilling with powered tools and equipment, the location of all underground utility services in the area shall be accurately determined and a danger to workers from those services shall be controlled.

(2) Excavation and drilling work in proximity to an underground service shall be undertaken in conformity with the requirements of the owner of the service.

(3) Pointed tools shall not be used to probe for underground gas and electrical services.

(4) Powered equipment used for excavating shall be operated so as to avoid damage to underground utility services and danger to workers.

Part XVIII EXCAVATION, UNDERGROUND WORK AND ROCK CRUSHING

Section 404 Definition

404. In this Part, "excavation" means a cut, cavity, trench or depression in the earth's surface resulting from rock or soil removal.

Section 405 Entrapment danger

405. (1) A worker shall not enter a place where there is a danger of entrapment unless safe access has been provided by catwalks, walkways or other acceptable means or he or she wears retrieval equipment satisfying the requirements of Part XXVII and is attended by another worker who is stationed, equipped and capable of immediately effecting a rescue.

(2) An area in which materials may be dropped, dumped or spilled shall be barricaded and protected by warning signs to prevent the inadvertent entry of workers.

Section 406 Pre-excavation requirements

406. (1) Before beginning excavation work with power tools or equipment in an area likely to have underground conduits, cables or pipelines, the location of the service facilities shall be accurately determined by the employer, marked by suitable means and communicated to the employee.

(2) Powered equipment shall not be used in a manner that exposes workers to harmful effects resulting from the damage to service facilities.

(3) Trees, boulders or other unsecured material located within 1.83 metres of the area to be excavated shall be secured or removed before excavation begins.

(4) A worker shall not enter an excavation over 1.22 metres deep unless

(a) the sides of the excavation are sloped to a safe angle and have been secured by the use of sheet piling, shoring and bracing or a trench box; or

(b) the worker is protected by other effective means.

(5) Added loads shall be considered in the design of the support system where

(a) equipment or other heavy objects are located or operated close to the edge of excavations;

(b) excavations are adjacent to or abutting buildings or other structures; or

(c) hazards are created by vibration from nearby equipment or passing vehicular traffic.

(6) Where there is a danger of undermining adjacent foundations, excavation work shall be done in short sections and the building walls shall be effectively shored or braced.

Section 407 Excavation or access

407. (1) Where a worker is required to enter an excavation greater than 1.22 metres deep, a ladder shall be provided in the immediate area where the worker is employed, extending from the bottom of the excavation to at least 0.91 metres above the top of the excavation.

(2) Walkways entering excavations shall be

(a) not less than 50.80 centimetres wide;

(b) equipped with guardrails when over 1.22 metres above grade; and

(c) provided with cleats when the grade is over 1/6.

(3) A runway which is used by mobile equipment shall be equipped with curbs.

Section 408 Removal of material

408. (1) A worker shall not permit excavated material to remain

(a) within 1.22 metres of the edge of a trench-type excavation; or

(b) within 1.52 metres of the edge of a pit-type excavation.

(2) Where skips or buckets are used to remove material from excavations, a horizontal shoring member shall be protected against dislodgement by the installation of vertical planking.

Section 409 Faces and slopes

409. (1) Where work is being carried on in an excavation

(a) the slopes shall be scaled and trimmed or otherwise stabilized to prevent slides of material or falls of rock;

(b) overhanging banks and trees or stumps and overburden shall be removed in the area within 5 metres from the edge of the excavation; and

(c) means shall be provided to prevent the erosion of the slope by surface water.

(2) Except where the minister, in writing, permits otherwise, in a pit, quarry or similar excavation

(a) the height of a face of which the material is not at a safe angle of repose shall not be greater than the height which can be safely reached by the equipment being used; and

(b) the bench height for sand, gravel and unconsolidated materials shall not exceed 5 metres and, in any event, shall not be higher than can be reached with equipment in use.

(3) A worker engaged in scaling, sloping or trimming banks or faces shall use a fall protection system that meets the requirements of Part X.

(4) Scaling and similar work shall be undertaken from the top down and the areas into which material may fall shall be kept clear of workers and equipment.

Section 410 Excavation safety

410. (1) Excavations shall be guarded by effective railings or barriers to prevent workers from falling in to excavations.

(2) Subsection (1) does not apply to a pit created to provide earth that can be used as fill at another site, referred to as a borrow pit.

(3) The accumulation of water in an excavation shall be prevented by effective means.

Section 411 Underground workings

411. (1) In an underground place of employment, including an excavation, natural entry, tunnel, raise, shaft or chamber, that is not a mine, the employment of workers shall be in accordance with

(a) standard engineering practices for the type of work being performed;

(b) the applicable requirements of these regulations; and

(c) additional requirements that the minister may consider necessary.

(2) Where an employer proposes to use methods or equipment that are new or do not comply with standard practices in underground workings, he or she shall first submit details of the proposed methods and equipment to the minister for approval and the submission shall include evidence of engineering feasibility with respect to the safety of the workers.