Page 173 - Electrical Installation in Hazardous Area

Area classification in areas which are not freely ventilated 139

/-- Extract
aidlow
Ihlnt.3 3)
Buildina bE(

Crack
+-- (Note

(Note
Air inlet __.
(Note I)
Door
Ground
Fig. 5.12 Secondary grade source of release with forced ventilation. Notes: (1)
Extract ventilation ensures that airflow at all apertures will be into building.
(2) Extract airflow sufficient to dilute maximum secondary grade source of
release to required fraction of LEL

Extract
air +

(Note 2)

Air inlet
-(Note 1)

Air inlet
-(Note 1)
Ground
a = Table 3.2 but 0.5 m minimum
Fig. 5.13 Primary grade source of release with extract ventilation. Notes: (1)
Ventilation ensures airflow is into the building in normal operation
restricting Zone 1 to inside building. (2) In abnormal circumstances
explosive atmosphere may leak from extract vent in addition to building
openings