Excavation and Trenching

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Did you know that the minimum slope for a trench is 1:1 (run: rise)? However, soil type and other conditions may require a slope of as much as 4:1 (run: rise).

Though often used grouped together, excavations and trenches are different. An excavation is a hole in the ground created by removing material, often soil or rock. A trench is a type of excavation deeper than it is wide. Excavation and trenching is inherently dangerous, common hazards include

  • Cave-ins
  • Materials falling into the excavation or trench
  • Being struck by moving equipment
  • Electrical contact, and
  • Falls from heights into the excavation or trench
  • Exposure to harmful or flammable gases that can collect inside the excavation or trench

The most important way to prevent injuries and reduce or eliminate hazards in excavation and trenching is to plan before you dig. Locate and mark gas and powerlines before digging and if those services pose a hazard, it must be shut off and disconnected. Plan how the excavation or trench will be dug and what will be done to prevent cave-ins and limit exposure to other hazards like harmful gases in the atmosphere.

Cave-ins are the most common cause of fatalities in excavations and trenches. Workers can be suffocated, crushed or buried by falling soil. An excavation or trench must be made in a way to prevent the collapse of its walls. In some cases, the walls can be sloped to prevent a cave-in. In other cases, shoring or bracing techniques can be used to prevent a collapse. Alternatively, trench cages can be used to protect workers should cave-in occurs.

An employer must:

  • Contact the local utility company or companies before starting excavation or trench and have the utility clearly locate and mark any utility lines to its end.
  • Sometimes a utility line that seems continuous may have different owners. Contact all the utility owners so that the whole of any utility line affected by a planned excavation or trench can be located and marked by a competent person.
  • Not allow people or objects to touch a utility line that has been located or marked, except if you are following the instructions of a competent person employed, contracted or authorized by owner or operator of the utility.
  • Support walls with adequate shoring or bracing, or use a certified trench cage in excavations or trenches deeper than 1.2 m that are used by workers. Shoring, bracing or a trench cage is not necessary if the excavation or trench is:
    • cut in sound and stable rock,
    • sloped to within 1.2 m of the bottom of the excavation or trench and the slope does not have a vertical rise of more than 1 m of to each 1 m of horizontal run, or
    • where soil overburden is located above an excavation or trench excavated in sound and stable rock, for the entire overburden and the slope does not have a vertical rise of more than 1 m of to each 1 m of horizontal run.
  • Have an engineer certify in writing that any slope the walls of an excavation or trench at an angle greater than a 1 m vertical rise to each 1 m horizontal run will be stable and not a hazard to anyone in the excavation or trench.
  • Make sure walls and crests cut into the rock are adequately supported by rock bolts, wire mesh or another type of protection.
  • Following the completion of a demolition project, make sure that
    • the demolition area is fenced or barricaded;
    • an excavation is backfilled to grade level; or
    • an excavation is sloped to its angle of repose.
  • Make sure any shoring, bracing or caging for the excavation or trench can support the increased load of any nearby powered mobile equipment. Strip the walls of an excavation or trench the walls of an excavation or trench of loose rock or other material that could slide, roll or fall on people in the excavation or trench and injure them.
  • Shore up any utility pole, building or other structure is if it could become unstable because of excavation or trenching. Alternatively, it may be removed entirely.
  • Install fences, guards or barricades near or at the sides of temporary excavations that are more than 1.2 m deep. Do not remove them unless it is necessary to excavate an area or perform other work.
  • Before anyone enters excavations or trenches that are at least 1.2 m deep, install a ladder extending at least 1 m above the excavation or trench. It is also acceptable to provide another way to enter or exit the trench as long as it is equally safe.
    • Entrances and exits must be at least 15 m from where a person is working.
    • If using a trench cage keep entrances and exits within the trench cage.
  • Keep the excavated material :
    • at least 1 m away from the edge of an excavation or trench. If keeping it any closer make sure an engineer certifies the shorter distance is safe ; and
    • far enough away from the edge of an excavation or trench so it does not fall back into the excavation or trench.
  • Keep excavations or trenches reasonably free of water if people are working in them.
  • Ensure any potentially hazardous atmosphere of an excavation or trench is safe before anyone enters it.
    • Test the atmosphere for hazardous gas, vapour or dust, flammables;
    • Follow the exposure limits established in Part 2: Occupational Health of the Workplace Health and Safety Regulations or make sure any concentrations hazardous gas, vapour, dust, or flammables in the atmosphere is not more than 50% of the lower explosive limit;
    • Test the oxygen levels to make sure the atmosphere is safe with neither too much nor too little oxygen. Saturation of oxygen in the atmosphere cannot be less than 19.5% or more than 22.5%, unless the employer can demonstrate that an unsafe oxygen level is not possible in their circumstance; and
    • Take adequate precautions to reduce the risk of injury to a person.
  • Have an engineer certify the design of trench cages used in an excavation or trench. Certification must include how deep the trench cage may be used and how it is supposed to be installed, erected, used, maintained and dismantled.
  • Make sure any alterations, repairs or modifications to a trench cage that may affect its structural integrity are certified by an engineer and meet all regulatory requirements.
  • Make sure, if a trench cage is below ground level, the soil above the cage is sloped to within 1.2 m of the bottom of the excavation or trench and is not at an angle greater than 1 m of vertical rise to each 1 m of horizontal run.
  • Make sure every trench cage has a permanently attached nameplate that is located where it is visible and can be read during inspections and while the trench cage is being used. All nameplates must identify the engineer that certified the cage’s design and state how deep the cage might be used.
  • Make sure a competent person inspects any trench cage daily before it is used to identify any defects or damage that may affect the structural integrity of the cage.
  • Remove a trench cage from service, if any defect or damage that affects the structural integrity is identified. Do not use that trench cage again until it is repaired and re-certified by an engineer.
  • Make sure trench cages rest as close as possible to the bottom of the excavation or trench. A trench cage should not rest above the maximum height specified by its design or 900 mm, whichever is less. An engineer’s certification is necessary to use a trench cage under different circumstances.
  • Make sure shoring or bracing for an excavation or trench is commercially manufactured or complies with an engineer certified design.
  • Install, build, maintain and dismantle any shoring or bracing for an excavation or trench according to the manufacturer's specifications or an engineer's specifications.
  • Make sure that loose rocks are scaled off the faces of excavations after a blasting operation ends and before other work is started or resumed in the blasting area.

An employee must:

  • Not enter an excavation or trench 1.2 m or more in-depth unless that a ladder is installed that extends at least 1m above the excavation or trench or some other adequate means of access and exit is provided.
  • Not work inside trenches if they are not adequately protected from cave-ins and other risks.
  • Not store hazardous substances in an excavation or trench.
(ae)"trench" means an excavation in which the excavation depth exceeds the excavation width.
Competent person” means a person who is
(i) qualified because of their knowledge, training and experience to do the assigned work in a manner that ensures the health and safety of every person in the workplace, and
(ii) knowledgeable about the provisions of the Act and regulations that apply to the assigned work, and about potential or actual danger to health or safety associated with the assigned work.
“Hazardous Substance” means chemical or biological material, dangerous goods within the meaning of the Dangerous Goods Transportation Act or a controlled product within the meaning of the Hazardous Products Act  (Canada) that is likely to, because of its harmful nature, cause injury or damage to the health or safety of a person exposed to it.

Workplace Health and Safety Regulations
N.S. Reg. 52/2013

Part 1 INTERPRETATION AND APPLICATION

Section 1.2 Definitions for these regulations

1.2 In these regulations,

"Act" means the Occupational Health and Safety Act ;

"adequate" means sufficient to protect a person from injury or damage to health;

"ANSI" means the American National Standards Institute;

"anchorage" means a secure connecting point capable of safely withstanding the impact forces, as prescribed in these regulations or an applicable standard, applied by a fall-protection system;

"approved" means approved by the Department or by an agency or authority designated or selected by the Department to make approvals;

"competent person" means a person who is

(i) qualified because of their knowledge, training and experience to do the assigned work in a manner that ensures the health and safety of every person in the workplace, and

(ii) knowledgeable about the provisions of the Act and regulations that apply to the assigned work, and about potential or actual danger to health or safety associated with the assigned work,

"CSA" means the Canadian Standards Association;

"certified" means meeting the requirements of a standard as attested to by a certification organization accredited by the Standards Council of Canada or an engineer;

"Department" means the Department of Labour and Advanced Education;

"designated" means, in relation to an employer, appointed in writing by the employer;

"emergency services agency" means an agency operating within the Province for the purpose of responding to emergencies, including

(i) a municipal police force required to be maintained under the Police Act, including the Royal Canadian Mounted Police,

(ii) fire departments,

(iii) ambulance services;

"engineer" means a person who is registered as a member or licensed to practise under the Engineering Profession Act and is competent to do the work being performed;

"latest version" means, in relation to a standard or other publication, the latest edition of the standard or publication as supplemented, amended, added to, replaced or superseded;

"manufacturer's specifications" means

(i) the written instructions of a manufacturer of a machine, material, tool or equipment that outline the manner in which the machine, material, tool or equipment is to be erected, installed, assembled, started, operated, used, handled, stored, stopped, adjusted, carried, maintained, repaired, inspected, serviced, tested, cleaned or dismantled, and

(ii) a manufacturer's instruction, operating or maintenance manual and drawings respecting a machine, tool or equipment;

"temporary highway workplace" means a temporary workplace on a highway, as defined in Part 24;

"work area" means a location at a workplace where an employee or self-employed person is working or may be required to work.

Part 2 OCCUPATIONAL HEALTH

Section 2.1 Definitions for Part 2

2.1 In this Part,

"physical agent", in relation to threshold limit values for occupational exposure, means an agent of acoustic, electromagnetic, ergonomic, mechanical or thermal nature;

"threshold limit values" means the threshold limit values established by the TLVs and BEIs that represent

(i) for chemical substances, the airborne concentrations of chemical substances and conditions under which it is believed that nearly all healthy workers may be repeatedly exposed, day after day, over a working lifetime, without adverse health effects,

(ii) for physical agents, the levels of exposure and conditions under which it is believed that nearly all healthy workers may be repeatedly exposed, day after day, without adverse health effects,

"TLVs and BEIs" means the latest version of the publication of the American Conference of Governmental Industrial Hygienists of threshold limit values and biological exposure indices.

Occupational Safety General Regulations
N.S. Reg. 44/99

Part 1 Title and Definitions

Section 2 Definitions

2. In these regulations,

(a) "Act" means the Occupational Health and Safety Act ;

(aa) "adequate" means sufficient to protect a person from injury or damage to health;

(b) "ALI" means the Automotive Lift Institute;

(ba) "angle of repose" means the angle with the horizontal at which material will no longer flow freely;

(c) "ANSI" means the American National Standards Institute;

(ca) "approved" means approved by the Department or by an agency or authority designated or selected by the Department to make approvals;

(d) "ASME" means the American Society of Mechanical Engineers;

(e) "ASTM" means the American Society for Testing and Materials;

(ea) "CGA" means the Compressed Gas Association;

(f) "CGSB" means the Canadian General Standards Board;

(g) "competent person" means a person who is

(i) qualified because of their knowledge, training and experience to do the assigned work in a manner that ensures the health and safety of every person in the workplace, and

(ii) knowledgeable about the provisions of the Act and regulations that apply to the assigned work, and about potential or actual danger to health or safety associated with the assigned work;

(ga) "compressed air" means air mechanically raised to a pressure higher than atmospheric pressure;

(h) "CSA" means the Canadian Standards Association;

(i) "demolition" means the destruction or removal of all, or part, of an existing building or structure;

(ia) "Department" means the Department of Labour and Advanced Education;

(j) "designated" means, in relation to an employer, appointed in writing by the employer;

(k) "electrical installation" means the wires, machinery, apparatus, appliances, devices, material and equipment used or intended for use for the generation, transmission, distribution, supply and use of electrical power or energy, and includes a power line and power line equipment;

(l) "engineer" means a person who is registered as a member or licensed to practise under the Engineering Profession Act and is competent to do the work being performed;

(m) "firefighter" means

(i) an employee who provides fire suppression services to the public from a fire department within a municipality or local service district, or

(ii) an industrial firefighter;

(n) "guardrail" means a fall protection system consisting of vertical and horizontal members that

(i) are capable of withstanding concentrated forces, as prescribed in these regulations or an applicable standard,

(ii) warn of a fall hazard, and

(iii) reduce the risk of a fall;

(o) "hazardous substance" means chemical or biological material, dangerous goods within the meaning of the Dangerous Goods Transportation Act or a controlled product within the meaning of the Hazardous Products Act (Canada) that is likely to, because of its harmful nature, cause injury or damage to the health or safety of a person exposed to it;

(p) "hoist" means a device or equipment and its structure used for lifting or lowering material, including cranes, an automotive lift, a winch, a chain fall or other similar device, but does not include a lift truck, a power operated elevating work platform, a device to which the Elevators and Lifts Act applies or a hoist that operates in a shaft in the underground at a mine;

(pa) "ITSDF" means the Industrial Truck Standards Development Foundation;

(q) "industrial firefighter" means an employee who

(i) is designated to fight fires at the employee's place of employment, and

(ii) is employed by an employer who does not, in the normal course of its business, provide fire suppression services to the public;

(qa) "latest version" means, in relation to a standard or other publication, the latest edition of the standard or publication as supplemented, amended, added to, replaced or superseded;

(r) "lift truck" means a lift truck as defined in the latest version of ANSI standard ANSI/ITSDF B56.1, "Safety Standard for Low Lift and High Lift Trucks";

(s) "locked out" means to have

(i) isolated the energy source or sources from a machine, equipment, tool or electrical installation,

(ii) dissipated any residual energy in a system, and

(iii) secured the isolation of the energy source or sources by an inhibiting device that is operated by a key or other process,

and to have performed a "lock-out" has a similar meaning;

(t) "machine" Repealed. [N.S. Reg. 52/2000, s. 1]

(u) "manufacturer's specifications" means

(i) the written instructions of a manufacturer of a machine, material, tool or equipment that outline the manner in which the machine, material, tool or equipment is to be erected, installed, assembled, started, operated, used, handled, stored, stopped, adjusted, carried, maintained, repaired, inspected, serviced, tested, cleaned or dismantled, and

(ii) a manufacturer's instruction, operating or maintenance manual and drawings respecting a machine, tool or equipment;

(ua) "mobile crane" means a mobile crane to which the latest version of CSA standard CSA Z150 , "Safety Code on Mobile Cranes" applies;

(v) "NFPA" means the National Fire Protection Association;

(va) "overhead crane" means any mechanical device or structure that is used to raise, lower and move material that travels overhead and that incorporates a

(i) power driven drum, bridge and cable or rope,

(ii) single or multiple girder, and

(iii) moveable bridge carrying a moveable or fixed hoisting mechanism,

but does not include wall cranes, cantilever gantry cranes and semi-gantry cranes;

(vb) "personal flotation device" means personal protective equipment that is capable of supporting a person with their head above water without the direct effort of the person wearing the equipment;

(w) "power line" means the above-ground or underground wiring that is used to distribute electricity;

(x) "power line equipment" means the components that are required to distribute electricity by means of a power line;

(y) "power operated elevating work platform" means a mobile horizontal working surface that provides access and support to a person at a workplace, and that is elevated and lowered by means of a mechanism and [that complies with] Part 23: Scaffolds and Other Elevated Work Platforms, of the Workplace Health and Safety Regulations made under the Act, including a standard listed in subsection (4) thereof;

(z) "powered mobile equipment" means self-propelled equipment that is designed to operate on land in conditions other than a public highway, but does not include equipment primarily designed to transport persons, a lift truck or a power operated elevating work platform;

(aa) "SAE" means the Society of Automotive Engineers;

(ab) "structural fire-fighting" means the activities of rescue, fire suppression and conservation of property from fires involving buildings, structures, vehicles, vessels, aircraft or other large objects constructed by human effort;

(ac) "surface mine" means a work or undertaking, other than a trench, for the purpose of opening up, proving, removing or extracting any metallic or non-metallic mineral or mineral bearing substance, rock, earth, clay, sand or gravel by means of an open excavation, and includes a pit or quarry;

(ad) "tower crane" means any mechanical device or structure that

(i) incorporates a power-driven drum and cable or rope and a vertical mast or tower and a jib,

(ii) is of the traveling, fixed or climbing type, and

(iii) is used exclusively for raising, lowering and moving material;

(ae)"trench" means an excavation in which the excavation depth exceeds the excavation width;

(af) "work area" means a location at the workplace at which an employee or self-employed person is or is likely to be working;

(ag) "worked" means drilled, blasted, extracted, excavated, loaded or subjected to other similar work.

[N.S. Reg. 52/2000, s. 1; 151/2003; 53/2013, ss. 1, 93]

Part 13 Premises and Building Safety, Construction and Demolition

Section 153 Underground utility lines

153. (1) In this Section,

(a) "utility line" means underground electrical, water, telephone, gas or other utility line or piping; and

(b) "physical limit" means the general location on the utility line where the utility's responsibility for the utility line ends.

(2) Where the location of any utility line is likely to endanger a person at a workplace, an employer must ensure that before beginning an excavation or trench the utility that owns or operates the utility line is contacted in order to have the utility clearly locate and mark the utility line to the physical limit of the utility line.

(3) The physical limit of the utility line in subsection (2) may be established by the utility based on reasonable factors the utility can identify to an employer.

(4) The utility must inform the employer if the employer has requested the utility to locate and mark a utility line or a portion of a utility line that is beyond the physical limit.

(5) Where a utility stops locating and marking a utility line because it has reached the physical limit of the utility line but the utility line continues, the employer must ensure the remainder of the utility line is located and marked by a competent person.

(6) Except as provided in subsection (7), an employer must ensure that no object or person comes in contact with a utility line located or marked in accordance with subsection (2) or (5).

(7) An object or person may come into contact with a utility line, whether up to the physical limit of the utility line or beyond the physical limit of the utility line, only under the following conditions:

(a) after the utility line has been located and marked in accordance with subsection (2) and (5); and

(b) the work involving the contact is performed by or in accordance with the instructions of a competent person who is employed, contracted or authorized by the utility that owns or operates the utility line.

[N.S. Reg. 53/2013, s. 68]

Section 162

162. Following the completion of a demolition project, an employer shall ensure that

(a) the demolition area is fenced or barricaded;

(b) an excavation is backfilled to grade level; or

(c) an excavation is sloped to its angle of repose.

[N.S. Reg. 53/2013, s. 71]

Part 14 Excavations and Trenches

Section 166

166. (1) Where a person may enter an excavation or trench and a wall of an excavation or trench is greater than 1.2 m in height, an employer shall ensure that the wall is supported by adequate shoring or bracing, or that an adequate trench cage is used, except where the employer is able to establish that the excavation or trench

(a) is cut in sound and stable rock;

(b) is sloped

(i) to within 1.2 m of the bottom of the excavation or trench, or

(ii) where soil overburden is located above an excavation or trench excavated in sound and stable rock, for the entire overburden,

and the slope does not exceed 1 m of vertical rise to each 1 m of horizontal run; or

(c) is one that a person does not enter within a horizontal distance from the walls of the excavation or trench that is equal to the height of the walls.

(2) Where the walls or crests of an excavation or trench are cut in rock, an employer shall ensure that the walls and crests are adequately supported by rock bolts, wire mesh or other means of adequate protection, if necessary, to ensure safe working conditions.

(3) Where powered mobile equipment is used near the edge of an excavation or trench, an employer shall ensure that any shoring, bracing or caging for the excavation or trench is adequate to support the increased load.

(4) An employer shall ensure that the walls of an excavation or trench are stripped of loose rock or other material that could slide, roll or fall on a person in the excavation or trench and injure that person.

(5) Despite clause. (1)(b), an employer may slope the walls of an excavation or trench at an angle that exceeds a 1 m vertical rise to each 1 m horizontal run where an engineer has certified in writing that the steeper slope will be stable and is not a hazard to a person in the excavation or trench.

(6) An employer shall ensure that a utility pole, building or other structure is provided adequate support or removed if the utility pole, building or other structure may become unstable because of excavation or trenching activity.

[N.S. Reg. 52/2000, s. 86]

Section 167

167. No person shall enter an excavation or trench 1.2 m or more in depth unless an employer ensures that a ladder is installed that extends at least 1 m above the excavation or trench or some other adequate means of access and exit is provided

(a) that is no more than 15 m from where the person is working; or

(b) where a trench cage is used, within the trench cage.

Section 168

168. An employer shall ensure that excavated material is

(a) kept at least 1 m away from the edge of an excavation or trench, unless an engineer certifies a shorter distance as adequate; and

(b) located a sufficient distance from the edge of the excavation or trench to ensure the excavated material does not re-enter the excavation or trench.

[N.S. Reg. 52/2000, s. 87]

Section 169

169. (1) An employer shall ensure that an excavation or trench in which a person works is kept reasonably free of water.

(2) Where a person may be exposed to a hazardous substance or to an oxygen rich atmosphere in an excavation or trench, an employer shall ensure that, before the person enters the excavation or trench,

(a) testing is performed to

(i) determine the concentration of any hazardous gas, vapour or dust, flammables, the concentration of oxygen and oxygen deficiency in the atmosphere in the immediate area of the excavation or trench where the work is to be performed,

(ii) ensure that the concentration of a chemical substance or a mixture of chemical substances in the excavation or trench does not exceed its occupational exposure limit under Part 2: Occupational Health of the Workplace Health and Safety Regulations made under the Act or 50% of its lower explosive limit, and

(iii) ensure that the level of oxygen in the atmosphere in the excavation or trench is not less than 19.5% and not more than 22.5%, unless the employer can demonstrate that an unsafe oxygen level is not possible in the circumstances; and

(b) adequate precautions are taken to reduce the risk of injury to a person.

(3) No person shall store hazardous substances in an excavation or trench.

(4) An employer shall provide, at or near the sides of all temporary excavations greater than 1.2 m in depth, fences, guards or barricades that prevent a person from falling into an excavation, and shall keep those fences, guards or barricades in place at all times, except where they interfere with the excavation or other work being done.

[N.S. Reg. 52/2000, s. 88; 53/2013, s. 73]

Section 170

170. (1) Where a trench cage is used in an excavation or trench, an engineer shall certify the design of the cage.

(2) An engineer shall include in the certified design required in subsection. (1) information on

(a) the depth at which the trench cage may be used; and

(b) the manner in which the trench cage is to be installed, erected, used, maintained and dismantled.

(3) Where a trench cage is altered, repaired or otherwise modified in a manner that may affect the structural integrity of the cage, an employer shall ensure that it meets the requirements of these regulations and is certified by an engineer in accordance with subsections. (1) and (2) prior to use after the alteration, repair or modification.

(4) Where the top of a trench cage is below ground level, an employer shall ensure that the soil above the cage is sloped in accordance with clause 166(1)(b).

Section 171

171. (1) An employer shall ensure that a nameplate is permanently attached to a trench cage, in a location visible for inspection when the cage is in use, identifying the engineer that certified the design of the trench cage and the depth at which the cage may be used.

(2) An employer shall designate a competent person to inspect a trench cage before each day it is used to ensure that it does not have any defects or damage that may affect the structural integrity of the cage.

(3) Where an inspection required in subsection (2) identifies a defect or damage that affects the structural integrity of the trench cage, an employer shall remove the cage from service until it is repaired and re-certified in accordance with subsection 170(3).

Section 172

172. An employer shall ensure that, where a trench cage is used, the cage

(a) rests as close as possible to the bottom of the excavation or trench; and

(b) does not rest above the bottom of the excavation or trench more than the designed maximum height, or 900 mm, whichever is the lesser,

unless an engineer certifying the design of the cage also certifies its use in the specific circumstances.

Section 173

173. (1) An employer shall ensure that shoring or bracing for an excavation or trench

(a) complies with a design certified by an engineer; or

(b) is commercially manufactured.

(2) An employer shall ensure that any shoring or bracing for an excavation or trench is installed, erected, maintained and dismantled in accordance with the manufacturer's specifications or an engineer's specifications.

Blasting Safety Regulations
N.S. Reg. 89/2008

Section 86 Removal of loose rocks

86. An employer must ensure that loose rocks are scaled off the faces of excavations after a blasting operation ends and before other work is started or resumed in the blasting area.