The Occupant Load Ratings are calculated by the Ministry of Municipal Affairs and Housing for the Province of Ontario using a number of different calculations and are found in the Ontario Building Code.

Some of these calculations are as follows:
• the size of the room or space
• number of doors providing direct access to egress routes and exits
• width of the doors
• type of seating: fixed theatre style or, movable tables and chairs
• do the occupants exit the building directly at ground level or do they have to use stairs or ramps
• width and length of the aisles
• space required for lectern, podium or stage

Once the numbers have been calculated, the only way they can be revised is through renovation and/or construction (change style of seating etc.).

If a lecturer were to increase the size of his/her class by letting the students bring extra chairs into the room or by letting the students sit in the aisles, they could conceivably be charged by the "Authority Having Jurisdiction" (Fire Department), if someone were to be injured, or worse, due to overcrowding during an emergency situation.

The following are excerpts from The Ontario Fire Code:

Section 2.7
Article 2.7.1.4.(1) The number of persons occupying a room or floor space in an assembly occupancy shall not exceed the occupant load for the intended use as determined in Sentence (2).

• (2) The occupant load for any room or floor space shall be the lower of
• (a) the occupant load as calculated in accordance with Sentences (3) to (7), or
• (b) the occupant load for which means of egress are provided as determined by the Building Code.