Hazardous Area Classification Basics: Zone 1/2 vs Zone 21/22

The first step in any explosion-proof project is always hazardous-area classification—working out where, and when, an explosive atmosphere may form. Get the zone wrong and the Ex equipment you choose is either wasted money or non-compliant.

Two families: gas vs dust

Flammable gas / vapour

Zone	Meaning
Zone 0	Explosive gas atmosphere present continuously or for long periods
Zone 1	Likely to occur in normal operation
Zone 2	Only briefly under abnormal conditions

Combustible dust

Zone	Meaning
Zone 20	Explosive dust cloud present continuously
Zone 21	Likely in normal operation
Zone 22	Only briefly under abnormal conditions

Typical zones by Hong Kong industry

• Pharma / Chinese medicine: ethanol extraction → often Zone 1 (gas); milling, granulation → Zone 21/22 (dust)
• Nutraceutical OEM: powder production → Zone 22; solvent steps → Zone 1/2
• Food processing: dusty environments → Zone 21/22
• Chemical / coatings / inks: flammable solvents → Zone 1/2

What comes after classification?

Once zones are defined, you can select matching Ex equipment (protection type, temperature class, IP rating) and complete design, installation and certification.

Not sure which zone your plant falls into?

Many Hong Kong industrial users have limited Ex knowledge—that's normal. We offer a free on-site assessment to quickly identify hazardous areas and compliance gaps. Get in touch.