Biogas Safety first!

Specific requirements
3. Requirements for holding tanks/preliminary pits
Technical protective measures
Holding tanks/preliminary pits for substrates inside
buildings must be equipped with a suitable (e.g.
explosion-protected) extraction unit with at least
five air changes per hour and flow monitoring with an
alarm in the event of failure.
Organisational protective measures
The equipment for extracting the gases must be automatically
switched on during the filling process.
Openings in the receiver tanks must remain closed
except during the filling process.
Satisfactory functioning of the extraction unit
must be checked prior to commissioning and the
results must be documented.
Classification of Ex zones
Holding tanks / preliminary pits:
Pit or tank, open or closed, for the receipt, buffer
storage and feeding of feedstock, in some cases
involving the mixing or recirculation of substrate
or digestate, with or without heating.
No zoning necessary, unless the manufacturer’s
instructions specify different classification of
zones.
Open holding tanks / preliminary pits outdoors:
Pit or tank for slurry, open across its entire crosssection,
with or without floating cover (no heating,
no substrate recirculation and no digestate
recirculation), gas accumulation not possible.
No zoning necessary, unless the manufacturer’s
instructions specify different classification of
zones.
Closed holding tanks / preliminary pits outdoors:
Pit or tank with a technically leak-tight cover;
even slight leaks are detected at an early stage
by regular checks; suitable gas displacement
with respect to the gas system in order to reliably
prevent overpressure and underpressure; leaktight
feedstock input thanks to loading below the
surface of the substrate. Closed receptacles of
this type also include receptacles with substrate
recirculation, substrate mixing and heating.
No zoning necessary, unless the manufacturer’s
instructions specify different classification of
zones.
Interior of closed holding tanks / preliminary pits:
Zone: same as the zone with the highest requirements
in the connected gas system.
Vicinity of closed holding tanks / preliminary pits:
No zoning necessary, unless the manufacturer’s
instructions specify different classification of
zones.
Covered holding tanks / preliminary pits without
substrate recirculation and without heating
outdoors:
Non-technically leak-tight receptacle, not connected
to the gas system. Has openings for filling.
No zoning necessary, unless the manufacturer’s
instructions specify different classification of
zones.
Holding tanks / preliminary pits for easily
degradable substrates:
Easily degradable feedstock materials include
liquid and paste-like biowastes. An adequate
flow rate (e.g. at least five times air change of the
pre-digester pit volume) is provided by monitored
extraction.
Zone 2: interior.
No zone: exterior.
Holding tanks / preliminary pits for slurry with
maximum fill level below ground level:
A sufficiently large opening area, e.g. through
grating covers; very low gas production rate as
a result of the low temperature.
Zone 2: interior
No zone: exterior
Insufficiently large opening area:
Air exchange takes place only during loading and
emptying processes. Very low gas production
because of the low temperature.
Zone 1: interior
Zone 2: in the immediate area surrounding
the openings
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