Biogas — methane + CO2 + H2S mix produced from organic waste. Farm, wastewater and industrial biogas plants are growing in Turkey (400+ facilities by end of 2024). Each poses explosion and H2S poisoning risks. NFPA 820 sets hazardous-area classification for wastewater treatment; biogas facilities follow it.
Biogas Composition
- Methane (CH4): 50-70% (primary combustible)
- CO2: 25-45% (inert but displaces O2)
- H2S: 50-5000 ppm (toxic + corrosive)
- Moisture, NH3, siloxane: Trace levels
- Production: anaerobic digester at 35-55 C; 20-40 day HRT
NFPA 820 Zone Classification
Hazardous location for wastewater/biogas:
- Class I Div 1 (Zone 0/1): Digester interior, gas holder, compressor interior
- Class I Div 2 (Zone 2): 3 m around digester, pump room
- Electrical equipment must be explosion-proof
- Ventilation: 12 ACH in pump/compressor room
H2S Poisoning Risk
H2S can become odorless (destroys olfactory nerve):
- 10 ppm: tolerated
- 100 ppm: dangerous within 1 hour
- 500 ppm: rapid death
- 1000+ ppm: instant death (knock-down)
Fixed H2S detection mandatory — 10 ppm alarm, 20 ppm evacuation.
Gas Holder Protection
Biogas collects in the membrane gas holder:
- Double-membrane: inner biogas, outer air (constant pressure)
- Overpressure relief: 5 mbar
- Vacuum relief: 2 mbar
- Flare: safely burns overpressure release
- Lightning protection: flame arrestors on all lines
Working Inside a Digester
Annual cleaning after draining the digester:
- Hot work permit (NFPA 51B) + confined space permit
- LEL below 10% (ventilation)
- H2S below 5 ppm
- O2 between 19.5% and 23.5%
- Personnel on SCBA + harness
- Rescue-ready standby outside
Turkey Biogas Project Notes
EPDK and the Ministry of Environment license biogas plants for fire/explosion safety. Design engineer checklist:
- Hazardous-area classification per ATEX 137 — drives material selection
- Flame-arrestor certification (ATEX + UL)
- H2S scrubber (biofilter or iron oxide) pre-combustion removal
- Flare or CHP (cogeneration) — never raw venting
- Training + annual drills
Biogas pipe calc with MEP Calc
Biogas line sizing, pressure drop, flame-arrestor placement and H2S scrubber flow calc.
Learn MorePrimary reference: NFPA 820 - Standard for Fire Protection in Wastewater Treatment and Collection Facilities. ATEX 137 directive and EN 60079 are supporting. NFPA official: NFPA 820.