Electrical safety standard (AS/NZS 60079.10.1:2009) defines areas of risk according to the likely presence of an explosive gas/air mixture. The inside of a fume cupboard, and the inside of all the duct, is defined to be a zone 1 (high) explosion risk. The space around the fume cupboard opening, extending 600mm in front and to both sides, right down to the floor, is defined to be a zone 2 (moderate) explosion risk.
The standard requires that electrical equipment (switches, power points, fans) shall not be fitted in such hazard zones unless suitably explosion proof.
These designated zones apply to all fume cupboards which do not comply in full with AS/NZS 2243.8. Compliant fume cupboards are re-classed as non-hazardous. Ordinary switches and power points can then be used, in specified locations. The criteria which achieve the non-hazardous qualification are:

• A warning label specifying spill capacity in the fume cupboard.
• A sump with raised front lip to contain spills.
• Balanced air flow through the open sash of at least 0.5m/sec average velocity.
• Continuous exhaust airflow monitor.
• Isolation of power and gas service outlets, (but not the fan, which must keep running). The isolator(s) must need to be manually re-set, and must operate.........
  manually in the case of an emergency (such as a chemical spill)
  automatically in the event of inadequate airflow
  automatically in the event of power failure
  automatically for at least 1 minute after starting the fan (pre-purge)
• The fan must operate for at least 20 minutes (or 5 min for schools) after the isolator operates (post-purge)

Wet Hazards

Switches and power points can never be fitted inside the fume chamber.