Floor Area’s Densification; Impact and Consequences on the Means of Egress

A new trend

Floor area densification is an increasingly common practice, especially in the context of reorganization projects for existing office space. The labour market has adapted to several realities, therefore, it is not uncommon to find that employers now seek to densify their workspaces so to leverage such spaces and improve the flexibility of office spaces. Computer technology progress and the increase of employers’ openness to teleworking have also contributed to this trend of shared office space.

Professionals who design such spaces often forget to validate if the means of egress can receive the occupant load produced by these office spaces. This validation shall be part of the designer’s priorities, especially when the project concerns an existing floor area layout.

The maximum exit capacity of the floor area shall be determined to ensure that the means of egress width is sufficient to allow the exit of all the occupants within a reasonable time.

How to Determine the Occupant Load On A Floor Area?

The occupant load shall be determined by Table 3.1.17.1. of Division B of National Building Code of Canada considering the intended occupancy or considering the number of seats, if more than the one determined from Table 3.1.17.1. [NBC 2010 amended QC, 3.1.17.1.(c)].

When a tenant occupies several storeys in the same building, some rooms shall be considered, such as meeting rooms and common spaces, may be used by the occupants of the other storeys.

In this situation, it will be incorrect to determine the occupant load at a level including meeting rooms and common spaces by applying 9.3 m2/person (occupation load required for offices) for the whole floor area, as if the meeting spaces were occupied only by the employees of that storey.

The proper way to proceed in this case would be to add up the number of persons estimated to meeting rooms and/or common areas, the number of persons estimated to office space, to obtain an occupant load corresponding to the all the premises of the floor area.

How to Determine the Maximum Egress Capacity of a Floor Area?

The maximum egress capacity of a floor area shall be determined by adding the maximum capacity of each exit serving the floor area. This value is obtained by multiplying the clear width of each exit by one of the rates required in accordance to Sentence 3.4.3.2. (1). We shall not forget that each exit cannot be more than 50% of the total width required for the exits [NBC 2010 amended QC, 3.4.3.2. (7)].

In case of an existing floor area reorganization, a simple verification of the dimensions on the layout plan is not sufficient. We also recommend to visually verify existing exit stairs as they circulate indoors to ensure that there is no clear width restriction. Moreover, validation of the dimensions of the steps and risers is favorable to ensure to use the correct rate required in Sentence 3.4.3.2.(1).

Work method

It is very useful to adopt a work method when it is time to perform this validation. Here below is an example of efficient work methods:

  • The creation of occupant load table for each floor area. This table lists all the rooms, their surface areas, occupancy rate to apply, as well as the number of persons per room.
  • The creation of maximum egress capacity table, where is listed all the floor area exits, their clear width, exits according to Article 3.4.3.2., as well as the maximum egress capacity.
  • The creation of a comparative table between the occupant load determined at step 1 and the maximum egress capacity for each floor area, permitting to validate that the occupant load of the floor areas does not exceed the maximum egress capacity.

Conclusion

In conclusion, when the densification of the floor area is desired, it may be necessary to modify the existing means of egress during the reorganization of the space since it must be kept in mind that the occupant load is limited to the total capacity of the exits serving the storey.

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By Marylène Cantatore, Architect, Codes and Standards – Fire Safety team

By |2019-06-25T15:07:57+00:00June 19th, 2019|News|0 Comments