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4.1.7.6.(1)
ApplicationIntent
OS1OS1
ObjectiveOS1 Fire Safety
Attribution
[F01-OS1.1]
Application
Application 1: 
Recirculation of exhaust air from mechanical ventilation systems required in Article 4.1.7.2., and where:
  • the flammable vapour concentration in the exhaust air is continuously monitored,
  • interlocks are provided so that if such concentration exceed 25% of the lower explosive limit, an alarm is sounded, recirculation is stopped and exhaust air is directed outside the building, and
  • Class I liquids are stored.
Exceptions: 
except where such storage consists only of closed containers and no dispensing operations are performed, or Class I or II liquids are processed, dispensed or used.
Exceptions: 
except:
  • as exempted in Sentences 4.1.1.1.(2) and (3), which apply to unique hazards in process plants, transportation, oil burning equipment, farms, isolated construction projects, and aerosol products, and
  • when in conformance with the appropriate provincial or territorial legislation.
Application 2: 
This also applies, as required in Clause 3.2.8.2.(1)(e), to dedicated storage rooms for cylinders of Class 2.1 flammable gases.
Exceptions: 
except:
  • where the quantities in a single fire compartment do not exceed 25 kg in the case of heavier-than-air gases,
  • where the quantities in a single fire compartment do not exceed those permitted in Sentence 3.2.8.2.(2) in the case of lighter-than-air gases,
  • as exempted in Sentence 3.1.1.4.(1), which applies to Class 2 gas manufacturing and dispensing facilities, and
  • for aerosols covered in Subsection 3.2.5.
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Intent
Intent 1: 
To remove the obligation, in Sentences 4.1.7.4.(1) and 5.4.5.2.(1), for exhaust air to be discharged outside the building and to permit its recirculation inside the building if a fail-safe system is provided. This is to limit the probability that vapour will accumulate, which could lead to the ignition of vapour from a nearby ignition source, which could lead to harm to persons.
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