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.
A recent fatality at a dairy farm in Eastern Ontario occurred when a worker made an unplanned entry into an oxygen-limited structure (silo) and was immediately overcome by the hazardous atmosphere. An employer must take every precaution reasonable in the circumstances to protect workers from hazards associated with entering silos. The recommended precautions are set out below. Entry into silos should only occur following written plans or procedures for work in these areas.
Oxygen-limiting silos keep oxygen out of the silo to reduce the degradation of the feed stored in them and, in doing so, create an oxygen deficient atmosphere inside the silo. The silo is equipped with "breather bags", which are open to the atmosphere either internally or externally, and which act as "lungs" to minimize silo pressure changes due to temperature variations throughout the day. In the warmth of the day, when the silo is heated by the sun, the gas trapped inside the silo expands and the bags "breathe out" and collapse. At night the silo cools, and the air inside contracts and the lungs "breathe in" and expand again. An oxygen-limited silo is sealed from the outside atmosphere, complete with a glass-lined coating inside and gasket bolts hold the side panels together. Typically, there are access hatches located at the bottom and at the top that are only large enough for a person to fit through. The release mechanisms for the access hatches must be manually removed to enable the hatch to be opened. A silo may vary in size ranging on average from 7 to 30 metres in height and from 6 to 12 metres in diameter. They are commonly used in dairy farming operations; however, they could be used in other agricultural applications for storage of corn feed, haylage or other feed. The feed is conveyed pneumatically and is blown through the top of the silo. Once full the silo is sealed tight.
These silos are intended to eliminate the oxygen content inside. Fermentation of the feed begins immediately. As fermentation progresses oxygen is used up. Fermentation consists of two stages: aerobic and anaerobic. The trapped oxygen in the silo is utilized during the aerobic stage then followed by the anaerobic stage. A critical time during the fermentation process occurs three to five days after the silo is filled during which time the oxygen is used up and nitrogen oxides reach their peak. The lack of oxygen is an imminent danger and can immediately overcome a person causing injury or death. Entry into oxygen-limited structures should be avoided by performing the task from outside the structure where possible; entry should be considered only when it is absolutely necessary to do so. Unplanned or inadvertent entries into these types of silos should never occur. The oxygen content will be reduced from normal atmospheric content of 20.9% to as low as 1%. In addition, other hazardous gases such as carbon dioxide, nitrogen dioxide, and methane may be present.
The Ontario Occupational Health and Safety Act applies with some limitations and conditions, to all farming operations (O. Reg. 414/05) that have paid workers under the Act. It does not apply to a farming operation operated by a self-employed person who does not have paid workers.
or contact the Ministry of Labour Health & Safety Contact Centre at 1-877-202-0008.
Remember that while complying with occupational health and safety laws, you are also required to comply with applicable environmental laws.
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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.