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Fire & Explosion Safety

Electrical Equipment

Duct Penetration

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Explosive Atmosphere

Explosion Hazard

 – A mixture of air, under atmospheric conditions,

and flammable gas, or vapour

 – Capable of self-sustaining propagation upon

ignition

 – Hazardous. If exploded, can cause damage

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Conditions for Explosion Hazard

AIR

Event of simultaneous occurrence of 

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Explosion Protection Concept

Explosion protection by removing one of the threefactors in fire triangle

1. Primary Protection (make safe)• Prevention of explosive atmosphere, example

 – Ventilation

 – inertization

2. Secondary Protection (encompass all electrical

apparatus used in hazardous areas)• Prevention of the ignition of explosive atmosphere

• Comply with IEC/EN 60079 or AS60079

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Hazardous Area Classification

• Explosive atmosphere is present, or may be

present for long period

• Allows selection of appropriate certifiedequipment

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Hazard Probability

• Zone 0

• Explosive gas atmosphere is present continuously

• Zone 1

•Explosive gas atmosphere is likely to occur in normaloperation

• Zone 2

• Explosive atmosphere is not like to occur in normal operation

• Non hazardous

• Explosive gas atmosphere is never present

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Gas or Apparatus Group

Decreasing MIE

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Ignition Characteristics

GAS OR

VAPOUR

LEL % UEL % MIE (µJ)

Propane 1.7 10.9 180

Ethylene 2.3 36 60

Hydrogen 4.0 77 19

Source: EEHA note

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LEL & UEL

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Explosive Limits (LEL & UEL)

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Temperature Class

Hydrogen auto ignition temperature is 560 C. Resultant classification may be T1.

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Typical Details

Duct Penetration B Wall

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Fire Damper

• Automatic closure of damper blade activated

by temperature (68-79C) within the duct

 – Rupture of frangible bulb causes the spring return

or operation of pneumatic actuator

• Manual closure independent and can override

the automatic means of control

 – Operation may be pneumatic or electric

• Open/close Indication of damper

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