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NFPA 820 - Mechanical Ventilation

Question asked by hazensawyer on Nov 23, 2016

2016 NFPA 820 Section 9.2.4 states:

9.2.4 All mechanically ventilated spaces shall be served by both
supply and exhaust fans, unless otherwise permitted by the
(1) For covered process facilities that are not routinely
entered by personnel and where mechanically ventilated,
the space shall be permitted to be ventilated by exhaust
fans only, and the induced supply (outside) air shall meet
the ventilation rate specified in the applicable chapter
when determining the area classification.
(2) Small aboveground buildings and structures, including
domes and covers, with a floor or surface of 9.3 m2
(100 ft2 ) or less that are physically separated from other
buildings or structures and do not present a fire hazard
to other buildings or structures shall be permitted to be
ventilated by a supply fan only.


Question 1: The purpose of NFPA 820 is to provide "a degree of fire and explosion protection for life, property, continuity of mission, and protection of the environment" and " to reduce or eliminate the effects of fire or explosion". It seems to make sense that Section 9.2.4 applies to a mechanical ventilation system designed for fire and explosion protection. However, if there is a space that has an odor control system (but is treated in all other aspects as if it is not ventilated), would I still need to provide a supply fan? or can I provide the odor control system that exhausts air and provide make up air louvers? Even though the space is technically being "mechanically ventilated", it is not provided for the purpose of fire and explosion protection. I don't see why a supply fan would be required. 


Question 2: Similar to the above, 9.2.4(1) uses the term "routinely entered by personnel". What is "routinely entered"? Is this once a week, once a month, once every 6 months, once a year? If a space that is only anticipated to be entered once a year or better yet once every 5 years, is this "routinely entered" and must be provided with both supply AND exhaust fans?


Thank you!