Under the original regulations (which remain in force until September 30 06), a confined space was typically defined as "a space in which, because of its construction, location, contents or work activity therein, the accumulation of a hazardous gas, vapour, dust or fume or the creation of an oxygen-deficient atmosphere may occur". In short, the potential for creation of hazardous atmosphere (for whatever reason) was the essential factor in determining whether a space was, or was not, a "confined space".

In the original definition, there was no consideration given to probability of occurrence in deciding whether there was potential, nor was the meaning of an "accumulation" defined. From the early 80s to the early 90s, these weaknesses in the original definition were typically not problematic, since the "textbook" understanding has always been that a "confined space" is one where atmospheric conditions could constitute an immediate danger to life or health. However, during the 90s, the definition was given increasingly broad (or some might say literal) application, and the notion of "accumulation" became problematic.

In offering this definition, the Ministry of Labour seemed to be trying to exclude from the definition certain types of spaces that might, arguably, be "primarily designed or intended for human occupancy". However, many thought that this "intent for human occupancy" aspect would not be exclusionary, since spaces such as arena refrigeration control rooms and similar mechanical rooms, while often not treated as "confined spaces", were not clearly spaces "primarily designed or intended for human occupancy" - rather, they were primary designed and intended to house machinery, some of which might contain hazardous gases, vapours, etc.

Under the new regulations, a confined space is defined as "a fully or partially enclosed space, (a) that is not both designed and constructed for continuous human occupancy, and (b) in which atmospheric hazards may occur because of its construction, location or contents or because of work that is done in it." From our perspective, this new definition has virtually the same meaning and consequences as the definition provided in the 2001 draft proposed regulation, and fails to achieve the goal of excluding spaces that are not "confined spaces" as they are traditionally understood by the occupational hygiene profession.

From our perspective, these conclusions don't make a lot of sense.

Firstly, the definition in the new regulation(s) does not draw any equivalency between being "designed and constructed for continuous human occupancy", and the frequency or regularity with which a worker enters or exits the space". If the intent of the new definition was to say "it is not a confined space if a worker enters and exits the space on a regular basis", the regulation could have said so, but it did not.

Secondly, just because a space serves as a "control room" does not mean that it was “designed and constructed for continuous human occupancy". Certainly some control rooms (like operator control rooms in power plants or production facilities) are intentionally designed and constructed for continuous human occupancy, and typically, there are no atmospheric hazards in these types of spaces under any circumstances. But, is it really the case that "arena chiller rooms" (which often contain large amounts of refrigerant gases in closed systems within small poorly ventilated rooms) are "designed and constructed for continuous human occupancy"? Would any architect who designed an ice rink agree that he or she designed the chiller room with the expectation of “continuous human occupancy” of that room? If an asphyxiation fatality occurred as a result of work on refrigerant systems in a chiller room, would saying "it wasn’t a confined space" be an effective statement of defense? From our perspective, an arena chiller room could meet the definition of "confined space" under the new regulation, and under the right set of circumstances, an atmospheric hazard could certainly arise in an arena chiller room.

Thirdly, the new definition, and the manner in which it appears to be interpreted, really fails to get at the underlying risk factors – namely, (1) the physical potential for toxic, explosive, or combustible substances being present at IDLH concentrations (immediately dangerous to life and/or health), or for IDLH oxygen depletion to occur, and (2) the likelihood or probability of such events occurring. It’s far from clear that the suitability of a space for “occupancy” (whatever that means) bears any predictable relationship to these risk factors.

The matter of how the definition is interpreted has significant implications for compliance with the new regulation(s). There are many different types of confined spaces, with different kinds of potential atmospheric hazards that arise for different reasons, under different sets of circumstances. As such, professional judgment will be key in determining whether a space is a "confined space" for purposes of the regulation; and for this reason, the regulation requires assessments of spaces to be performed by persons with adequate training, skills and experience. More liberal interpretation will result in a larger the number of spaces being classified as "confined spaces", and this in turn will determine the level of financial and human resources needed for confined space program implementation and management.