Biogas Safety first!

Specific requirements
6. Requirements for wooden roof structures in gas storage systems
Wooden roof structures are often used as a substructure
for gas storage systems. As wooden roof
structures in biogas storages are exposed to particular
conditions, and visually indiscernible damage
to wood reduces the load-bearing capacity of
the beams to such an extent that they are liable to
fail without notice, a special approach to checking
structural stability must be used for the sake of the
safety of all persons charged with inspection/maintenance
work.
Technical protective measures
Whenever wooden roof structures are used it is important
to make sure that the structural analysis calculations
take account of the unusual environment,
water saturation and sulphur deposits. In order to
guarantee the stability of the wooden structure, reinforcements
must be installed between the beams.
It is also necessary to choose suitable quality timber
that is precision-cut to size.
The supporting construction of the timber beams
must be designed such that the beams are prevented
from slipping out if they become deformed.
Organisational protective measures
In order to ensure the stability of wooden roof structures,
regular visual inspections and checks must be
carried out during operation to identify any abnormalities.
If the tank is opened for operational reasons,
a load test must be performed prior to walk-on access.
Regular checks of timber roof structures
Regular visual inspection through sight glasses
by the persons responsible (operator, person appointed
by the operator or specialised firm) for:
ZZ
conspicuous deformation, irregularities,
breaks or splintering, for the purpose of ruling
out acute apparent danger during subsequent
investigative steps.
Regular checks regarding abnormalities in
operation by the persons responsible (operator,
person appointed by the operator or specialised
firm) for:
ZZ
damage to or malfunctions in agitators, screw
conveyors, etc.
ZZ
pieces of wood in pumps, coarse material
screens or separators.
The aim is to detect damage at an early
stage and prevent economic consequences.
Ad hoc check
Checking carried out in the course of
opening of the tank for operational
reasons by the persons responsible
(operator, person appointed by the
operator or specialised firm):
ZZ
A load test must be performed
before anyone steps on the wooden
roof structure.
ZZ
The load test must be carried out
with a load calculated according
to the formula below at at
least three representative points
in midspan (centre of a beam in
the longitudinal direction). If the
entire area is affected, testing of
the roof structure must be carried
out on at least every third beam
and on particularly conspicuous
or sagging beams. The test load
must be applied for a period of at
least three minutes in midspan.
This can be done with a crane, for
example.
The method to be used for calculating the
load needed to test the load-bearing capacity of the
timber beams is as follows:
With cladding on the beams:
Area for loading a timber beam:
A = e× R
2 (m2 )
e = spacing between beams
R = radius in meters
Test load (concentrated load in midspan) for the
load test: P = A× 75
2 (kg)
Minimum test load: 200 kg concentrated load
per person, on each beam on which a person or
persons will walk.
Without cladding on the beams:
In this case the load can be produced for example
by a pallet with a water tank,
placed on supporting beams (12/12 cm).
Area for loading a timber beam: A = e× R
2 (m2 )
Test load (concentrated load in midspan) for the
load test: P = A× 75
2 (kg)
Minimum test load: 200 kg concentrated load
per person, on each beam on which a person or
persons will walk.
photo: Ökobit GmbH
Wooden roof structure of a digester
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