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Occupational Health and Safety Act: The Government department in Alberta that administers the Occupational Health and Safety Act and Regulations made under that Act.

Occupational illness: Any abnormal condition or disorder, other than one resulting from an occupational injury, caused by exposure to environmental factors associated with employment. It includes acute and chronic illnesses or diseases that may be caused by inhalation, absorption, ingestion, or direct contact.

Occupational injury: Any such injury such as a cut, fracture, sprain, amputation, etc., which results from a work accident or from a single instantaneous exposure in the work environment.

Ohm: The unit by which resistance to electrical current is measured. From Ohm's Law (Current=Voltage/Resistance, or in other words, Current=Voltage/Ohms), a mathematical expression of the relationship between these three elements.

Opening statement: The factual presentation given by an attorney at the beginning of a case. The defendant's attorney has the option of delaying his opening statement for the defense until the plaintiff's evidence has been introduced.

Opening: A gap or void 30 inches (76 cm) or more high and 18 inches (48 cm) or more wide, in a wall or partition, through which employees can fall to a lower level.

Open sides and ends: The edges of a platform that are more than 14 inches (36 cm) away horizontally from a sturdy, continuous, vertical surface (such as a building wall) or a sturdy, continuous horizontal surface (such as a floor), or a point of access. Exception: For plastering and lathing operations the horizontal threshold distance is 18 inches (46 cm).

Operating Work Site: The specific location of a work activity where work is not limited to office activities. Eg.: drilling sites, maintenance shops and laboratories.

Overcurrent: Any current in excess of the rated capacity of equipment or of a conductor.

Overhand bricklaying: The process of laying bricks and masonry units such that the surface of the wall to be jointed is on the opposite side of the wall from the mason, requiring the mason to lean over the wall to complete the work. Related work includes mason tending and electrical installation incorporated into the brick wall during the overhand bricklaying process.