Vinyl chloride monomer (VCM, CH2=CHCl) is a flammable carcinogenic gas/liquid used in PVC manufacture. LEL 3.6%, UEL 33%, flash point −78 °C. Closed tank leaks quickly form explosive atmospheres. ATEX 2014/34/EU and NFPA 30 require explosion-protected design for VCM tanks, transfer pumps and piping.
VCM Properties
- Molecular weight: 62.5 g/mol
- Boiling point: −13.4 °C (atmospheric)
- LEL: 3.6% by volume
- UEL: 33% by volume
- Autoignition: 472 °C
- IARC: Group 1 carcinogen (linked to liver angiosarcoma)
ATEX Zone Classification
- Zone 0: Tank ullage - continuous VCM vapor
- Zone 1: Tank vent outlet, pump seal, loading arm (explosive atmosphere likely in normal operation)
- Zone 2: 3 m radius around Zone 1 (only short-term, under fault or abnormal conditions)
- Equipment category: II 2G Ex db IIA T2 (VCM gas group IIA)
Explosion Pressure
VCM maximum explosion pressure: Pmax = 8.8 bar (1 atm initial).
Deflagration index Kst: 50 bar·m/s (St1 class).
NFPA 68 venting equation: Av = (Kst × V0.75) / (Pred × 1000). For a 100 m³ volume with Pred = 0.5 bar, Av = 50 × 31.6 / 500 ≈ 3.2 m² of vent panel — two 1.6 m² panels are a practical choice.
Fire Protection
- Deluge water spray: 10 L/min/m² tank cooling
- Foam: Alcohol-resistant AFFF (VCM is not a polar solvent, but it can polymerize at fire temperatures, so a standard AFFF film is not sufficient)
- Gas detection: Catalytic or IR, alarm at 20% LEL, emergency shutdown (ESD) at 40% LEL
- Emergency shutdown: isolation of all transfer lines in under 30 s
- Ventilation: 12 air changes per hour, explosion-protected (Ex) fan
ATEX ventilation with MEP Calc
MEP Calc supports air-change sizing, ESD flow, explosion pressure and vent area calculations for VCM storage.
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Download SprinkCalc on the App StoreNFPA 30, ATEX 2014/34/EU, IEC 60079-10-1, NFPA 68, IARC Monographs. NFPA 30 Flammable Liquids code.