Print Print This Page

Timber Dome Structure Failures

  • Issued: September 2, 2014
  • Content last reviewed: September 2014

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.

Hazard summary

This information bulletin is intended to raise awareness about the potential for serious injuries that could result from the collapse of timber dome structures. Timber dome structures are usually used by transportation and road maintenance authorities, municipalities, and snow removal contractors to protect and store sand and salt used for winter road maintenance.


In March and April 2014, four timber dome structures collapsed in various locations in Ontario. Each collapse was started by an unbalanced snow load that was imposed on the structure – usually at the lower panels of the domes. Contributing factors may have included a lack of snow removal at the base of the domes, inadequate structural inspections, construction issues with the panel glued joints and the lack of a maintenance program.

Hazard location

Timber dome structures are located throughout Ontario. A large number of these are in exposed areas that are frequently subject to weather extremes, such as heavy snow and high wind. In addition, these timber dome structures are highly susceptible to heavy equipment damage. These factors, if not monitored, will reduce the service life of the individual structural components, which undermines the structural integrity of the entire dome and can lead to structural collapse.

Recommended precautions and control measures

Employers and owners of timber dome structures should have the structural integrity of the domes inspected by a professional engineer (P.Eng) familiar with timber dome construction. Any design flaws or other deficiencies identified by the P.Eng should be repaired and corrected as recommended.

Requirements under the Occupational Health and Safety Act

Relevant legal requirements under the Occupational Health and Safety Act (OHSA) include but are not limited to:

  • An employer shall ensure that a building, structure, or any part thereof, or any other part of a workplace, whether temporary or permanent, is capable of supporting any loads that may be applied to it,
    • as determined by the applicable design requirements established under the version of the Building Code that was in force at the time of its construction,
    • in accordance with such other requirements as may be prescribed, or
    • in accordance with good engineering practice, if subclauses (i) and (ii) do not apply. (OHSA clause 25 (1)(e)(i), (ii), and (iii))
  • An employer shall acquaint a worker or a person in authority over a worker with any hazard in the work, and in the handling, storage, use, disposal and transport of any article, device, equipment, or a biological, chemical or physical agent (OHSA clause 25(2)(d)). For example, workers should be aware of any hazards involved in operating heavy equipment in or around timber domes.
  • An employer shall provide information, instruction and supervision to a worker to protect the health or safety of the worker (OHSA clause 25(2)(a)). Such information and instruction may include the importance of removing snow around the base of the domes.
  • An employer shall take every precaution reasonable in the circumstances for the protection of a worker (OHSA clause 25(2)(h)), including those working in or around timber domes.


  • "Sand Domes Inspection Manual (SDIM)" published in 1988 by the Structural Office Highway, Engineering Division of the Ministry of Transportation.
  • Occupational Health and Safety Act

For more information, contact the Ministry of Labour Health & Safety Contact Centre toll free at 1-877-202-0008.

ISBN 978-1-4606-4613-7 (HTML)

Disclaimer: This web resource has been prepared to assist the workplace parties in understanding some of their obligations under the Occupational Health and Safety Act (OHSA) and the regulations. It is not intended to replace the OHSA or the regulations and reference should always be made to the official version of the legislation.

It is the responsibility of the workplace parties to ensure compliance with the legislation. This web resource does not constitute legal advice. If you require assistance with respect to the interpretation of the legislation and its potential application in specific circumstances, please contact your legal counsel.

While this web resource will also be available to Ministry of Labour inspectors, they will apply and enforce the OHSA and its regulations based on the facts as they may find them in the workplace. This web resource does not affect their enforcement discretion in any way.