Formwork and Shoring

Did you know?

Did you know that if a person may be exposed to a hazardous substance in an excavation or trench, testing must be performed in the working area before anyone is allowed to enter and adequate precautions must be taken to reduce the risk of injury?

Summary

Formwork refers to the total system of support for freshly placed concrete, including the mould or sheathing, supporting members, hardware, and necessary bracing. Shoring is a system of vertical or inclined supports for forms; it may be of wood or metal posts, scaffold-type frames, or various patented members or other systems of falsework. Shoring is typically used to support such things as formwork, floors immediately following removal of formwork, buildings and excavation or trench sidewalls. Improper design, erection, or dismantling of formwork or shoring can have severe consequences, including fatalities.

Hazards related to formwork and shoring include:

  • Failure of formwork, releasing the contents and destabilizing larger structures.
  • Collapsing of excavation or trench sidewalls, formwork or structures being supported (e.g., trench cave-in).
  • Falling objects.
  • Employees falling from heights.
  • Being struck by moving machinery, tools, and equipment.

Some reasons why formwork and shoring could fail include:

  • Not designed or certified by a qualified engineer.
  • Not following the engineer’s specifications and designs.
  • Design or construction that does not follow engineer certified plans or manufacturer specification.
  • Not accounting for all factors that could impact structural integrity (e.g., wind).
  • No or inadequate inspections and maintenance of formwork or shoring.
  • Premature removal of formwork or shoring.
  • Loading formwork or shoring beyond limits.
  • Using equipment that is defective or has reduced structural integrity.
  • Improper foundation (e.g., type and condition of soil).
  • Use of shortcuts or inappropriate steps to cut costs.
  • Unclear instructions or lack of training.

An employer must make sure that, when at a project:

  • All bracings and supports for a part of the project are completed before beginning any work that puts a load on that part. [N.S. Reg. 44/99, s. 154(1)(a)]
  • Bracing is used on all free-standing walls of brick, concrete blocks, or similar materials taller than 2 metres from both sides until the wall is attached to a rigid structure and the mortar has set adequately. [N.S. Reg. 44/99, s. 154(1)(b)]
  • Bracing is used on all walls or structures designed to support any part of a roof or load to prevent collapse. [N.S. Reg. 44/99, s. 154(1)(c)]
  • Erect all columns in such a way that it does not collapse, and brace if necessary. [N.S. Reg. 44/99, s. 154(1)(d)]
  • Use bracing or shoring for support beneath floor levels where concrete is poured. [N.S. Reg. 44/99, s. 154(2)]
  • All bracing or shoring must comply with the latest version of CSA standard CSA S.269.1, “Falsework for Construction Purposes.” [N.S. Reg. 44/99, s. 154(4)]
  • All bracing and shoring must be designed by an engineer and all related work must be done according to the engineer’s certified specifications, as specified in the CSA Standard CSA S.269.1 in Section 8.4.7.4.
  • The footings for shoring and bracing must be designed to support the maximum load that might be put on them without excessive settlement or deformation. [N.S. Reg. 44/99, s. 154(5)]

An employer must make sure that the following occurs when working in or near excavations and trenches:

  • If a person has to enter the excavation or trench, sidewalls taller than 1.2 metres must be supported with adequate shoring or bracing, or use a trench cage. [N.S. Reg. 44/99, s. 166(1)]. These measures are not required if the employer establishes that the excavation or trench:
    • is cut in sound and stable rock; [N.S. Reg. 44/99, s. 166(1)(a)]
    • is sloped to within 1.2 metres of the bottom of the excavation or trench, or when soil overburden is located above an excavation and the trench is excavated in sound and stable rock, the overburden must be sloped. In either case, the slope must not exceed 1 metre of vertical rise to each 1 metre of horizontal run. An exception may be possible if certified by an engineer. [N.S. Reg. 44/99, s. 166(1)(b) and s.166(5)]
    • 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 (i.e., one where a person who enters is far enough away that a wall could not collapse on them). [N.S. Reg. 44/99, s. 166(1)(c)]
  • The walls and crests of an excavation or trench cut in rock are supported with rock bolts, wire mesh, or other means of adequate protection. [N.S. Reg. 44/99, s. 166(2)]
  • The shoring, bracing, or caging used can support the extra load from any powered mobile equipment used near the edge of the excavation or trench. [N.S. Reg. 44/99, s. 166(3)]
  • The walls are stripped of loose rocks or other material that could slide, roll, or fall on and injure a person. [N.S. Reg. 44/99, s. 166(4)]
  • A utility pole, building, or other structure that may become unstable is adequately supported or removed. [N.S. Reg. 44/99, s. 166(6)]
  • Do not allow anyone to enter an excavation or trench that is 1.2 metres deep or more unless a ladder is installed that extends at least 1 metre above the opening or another adequate means of access and exit is provided. The ladder or alternative must be no more than 15 metres from where the person is working, or within a trench cage. [N.S. Reg. 44/99, s. 167]
  • Excavated material must be kept at least 1 metre away from the edge of an excavation or trench unless an engineer certifies a shorter distance , and must be far enough away from the edge that the material does not re-enter the opening. [N.S. Reg. 44/99, s. 168]
  • An excavation or trench in which a person works must be kept reasonably free of water. [N.S. Reg. 44/99, s. 169(1)]
  • If a person may be exposed to a hazardous substance or an oxygen-rich atmosphere in an excavation or trench, testing must be performed to determine the concentration of the hazardous substance and oxygen in the working area before they are allowed to enter. Adequate precautions must be taken to reduce the risk of injury. [N.S. Reg. 44/99, s. 169(2)(a)(i) and s.169(2)(b)]
  • Make sure that the concentrations of all substances are in full compliance with the occupational exposure limit under the Workplace Health and Safety Regulation or 50% of its lower explosive limit before a person is allowed to enter. [N.S. Reg. 44/99, s. 169(2)(a)(ii)]
  • Make sure that the oxygen level is not less than 19.5% and not more than 22.5% before a person is allowed to enter, unless it can be demonstrated that an unsafe oxygen level is not possible and adequate steps are taken to reduce the risk of injury. [N.S. Reg. 44/99, s. 169(2)(a)(iii)]
  • No person must be allowed to store hazardous substances in an excavation or trench. [N.S. Reg. 44/99, s. 169(3)]
  • Provide and maintain fences, guards, or barricades that prevent a person from falling into a temporary excavation that is deeper than 1.2 metres, except when they interfere with the excavation or other work. [N.S. Reg. 44/99, s. 169(4)]
  • Make sure that shoring or bracing complies with a design certified by an engineer or is commercially manufactured. [N.S. Reg. 44/99, s. 173(1)]
  • Make sure that shoring or bracing is installed, erected, maintained, and dismantled in accordance with the engineer’s or manufacturer's specifications. [N.S. Reg. 44/99, s. 173(2)]

The Nova Scotia Temporary Workplace Traffic Control Manual requires that employers make sure concrete barriers are placed along an excavation or trench that is 0.3 metres in depth or more when that excavation or trench is at or near a street, road or highway and the worksite is left unattended.

An employer must make sure that the following occurs when using trench cages:

  • An engineer must certify the design of any trench cage used, and the certification must include information on how to install, erect, use, maintain, dismantle, and the depth at which the trench cage may be used. [N.S. Reg. 44/99, s. 170(1) and (2)]
  • Make sure if a trench cage is altered, repaired, or modified that it still meets the requirements of the regulations and are certified by an engineer before it is used again. [N.S. Reg. 44/99, s. 170(3)]
  • Where the top of a trench cage is below ground level, make sure that the soil above the cage is sloped to within 1.2 metres of the bottom of the trench or where the soil overburden is located above a trench excavated in sound and stable rock and the slope does not exceed 1 metre of vertical rise to each 1 metre horizontal run. [N.S. Reg. 44/99, s. 170(4))]
  • Make sure that each trench cage has an easily visible permanent nameplate that states the engineer who certified the cage’s design and the depth at which it can be used. [N.S. Reg. 44/99, s. 171(1)]
  • Make sure that a trench cage is inspected by a designated competent person each day before it is used to be sure that it does not have any defects or damages that may affect its structural integrity. [N.S. Reg. 44/99, s. 171(2)]
  • Remove a trench cage from service if it is found that a defect or damage affects its structural integrity until it is repaired and re-certified by an engineer. [N.S. Reg. 44/99, s. 171(3)]
  • Make sure that the trench cage rests as close as possible to the bottom of the excavation or trench unless the engineer that certifies the cage’s design also certifies its use in special circumstances. [N.S. Reg. 44/99, s. 172(a)]
  • Make sure the bottom of the trench cage does not rest above the bottom of the excavation or trench at more than the designated maximum height or 900 mm from the bottom, whichever is less, unless the engineer that certifies the cage’s design also certifies its use in special circumstances. [N.S. Reg. 44/99, s. 172(b)]

Employees do not have specific requirements under the regulations related to formwork and shoring, but they still have a part to play in protecting their safety.

An employee must:

  • Take every reasonable precaution to protect their own safety and the safety of others at or near the workplace. This action can mean following the engineer’s designs when installing, erecting, using, and dismantling formwork and shoring, using equipment as trained, and following safe work procedures. [S.N.S. 1996, c.7, s. 17(1)(a)]
  • Co-operate with your employer and other employees to protect their own safety and the safety of others at or near the workplace. [S.N.S. 1996, c.7, s. 17(1)(b)]
  • Wear or use the necessary personal protective equipment or devices. [N.S. Reg. 44/99, s. 9]
  • Report any aspect of the workplace that is or may be dangerous to their own safety or that of others in the workplace. [S.N.S. 1996, c.7, s. 17(2)]
  • Be trained and supervised as necessary.

Legislation

OCCUPATIONAL HEALTH AND SAFETY ACT

S.N.S. 1996, c. 7

Section 17

17. (1) Every employee, while at work, shall

(a) take every reasonable precaution in the circumstances to protect the employee's own health and safety and that of other persons at or near the workplace;

(b) co-operate with the employer and with the employee's fellow employees to protect the employee's own health and safety and that of other persons at or near the workplace;

(c) take every reasonable precaution in the circumstances to ensure that protective devices, equipment or clothing required by the employer, this Act or the regulations are used or worn;

(d) consult and co-operate with the joint occupational health and safety committee, where such a committee has been established at the workplace, or the health and safety representative, where one has been selected at the workplace;

(e) co-operate with any person performing a duty or exercising a power conferred by this Act or the regulations; and

(f) comply with this Act and the regulations.

(2) Where an employee believes that any condition, device, equipment, machine, material or thing or any aspect of the workplace is or may be dangerous to the employee's health or safety or that of any other person at the workplace, the employee shall

(a) immediately report it to a supervisor;

(b) where the matter is not remedied to the employee's satisfaction, report it to the committee or the representative, if any; and

(c) where the matter is not remedied to the employee's satisfaction after the employee reports in accordance with clauses (a) and (b), report it to the Division.


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 3 Personal Protective Equipment

Section 9 Use of personal protective equipment

9. (1) An employer shall ensure that adequate personal protective equipment or devices required for an assigned task are used, based on

(a) the nature of the task;

(b) the location and conditions of the workplace; and

(c) any hazards that may affect the health and safety of persons in the workplace.

(2) Where personal protective equipment or devices are required under the Act or these regulations, an employer shall ensure that

(a) an employee receives adequate training in the proper use and care of the personal protective equipment or devices; and

(b) an employee wears or uses the personal protective equipment or devices in accordance with the instruction and training provided.

(3) An employer shall ensure that all personal protective equipment or devices required under the Act or these regulations are

(a) maintained by a competent person; and

(b) tested or visually inspected before each use,

in accordance with the manufacturer's specifications.

(4) Where a person identifies any defect in personal protective equipment or devices that may impair the adequacy of the equipment or devices, the employer shall ensure that the personal protective equipment or devices are not used until they are repaired.

[N.S. Reg. 52/2000, s. 3; 53/2013, s. 93]

Part 13 Premises and Building Safety, Construction and Demolition

Section 154 Bracing and supports

154. (1) An employer at a project shall ensure that

(a) work is completed on any component designed to support or give added support to a part of the project before proceeding with any work that adds to the load on that part;

(b) a free standing wall of brick, concrete blocks or similar materials greater than 2 m in height is braced from both sides until the wall is attached to a rigid structure and the mortar has set adequately;

(c) a free standing wall or structure designed to support roof components or any load is braced in an adequate manner to prevent collapse of the wall or structure; and

(d) a column is erected in an adequate manner to prevent collapse of the column and, where further support is required to ensure that the column does not collapse, braced in an adequate manner.

(2) An employer at a project shall use bracing or shoring for support beneath floor levels where concrete is being poured.

(3) An employer at a project shall

(a) ensure that bracing or shoring is designed by an engineer and is erected, maintained and dismantled in accordance with the engineer's certified specifications; or

(b) retain the bracing or shoring at all floor levels beneath the floor where concrete is being poured until the removal of the bracing or shoring is authorized in writing by an engineer.

(4) An employer shall ensure that any bracing or shoring referred to in this Section complies with the latest version of CSA standard CSA S269.1 , "Falsework for Construction Purposes."

(5) An employer shall ensure that footings for shoring and bracing are designed to support the maximum load likely to be imposed, without excessive settlement or deformation.

[N.S. Reg. 53/2013, s. 69]

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.