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Safety and environmental standards for fuel storage sites
Final report
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100 Again, this could be done per tank, or more conservatively, standardised at the longest
margin time for a group of or all tanks. In all cases, however, it should be recorded in writing.
Response time 1: Normal fill level to LAH
101 The normal fill level should be close enough to the LAH to enable overfilling to be rapidly
detected (and to maximise the usable capacity of the tank), but should be set an adequate margin
below the LAH to prevent spurious operation of the alarm, eg due to liquid surge or thermal
expansion at the end of an otherwise correctly conducted transfer.
102 Separation between the normal fill level and the LAH may also help to discourage
inappropriate use of the LAH to control the filling operation.
103 Appendix 3 contains worked examples of the application of this guidance for setting tank
capacities.
Fire-safe shut-off valves
104 Each pipe connected to a tank is a potential source of a major leak. In the event of an
emergency it is important to be able to safely isolate the contents of the tank. Isolation valves
should be fire-safe, ie capable of maintaining a leak-proof seal under anticipated fire exposure.
Fire-safe criteria
105 Fire-safe shut-off valves should be fitted close to the tank on both inlet and outlet pipes.
Valves should either conform to an appropriate standard (BS 6755-2
14
or BS EN ISO 10497
15
),
equivalent international standards or be of an intrinsically fire-safe design, ie have metal-to-metal
seats (secondary metal seats on soft-seated valves are acceptable), not be constructed of cast
iron and not be wafer bolted.
Remotely operated shut-off valves (ROSOVs)
106 In an emergency, rapid isolation of vessels or process plant is one of the most effective means
of preventing loss of containment, or limiting its size. A ROSOV is a valve designed, installed and
maintained for the primary purpose of achieving rapid isolation of plant items containing hazardous
substances in the event of a failure of the primary containment system (including, but not limited to,
leaks from pipework, flanges and pump seals). Valve closure can be initiated from a point remote
from the valve itself. The valve should be capable of closing and maintaining tight shut off under
credible conditions following such a failure (which may include fire).
107
Remotely operated shut-off valves (ROSOVs) for emergency isolation of hazardous
substances: Guidance on good practice
HSG244
16
provides guidance on how to assess the need
to provide ROSOVs for emergency isolation. It has been written for a wide range of circumstances
and as a result the section dealing with ROSOV failure modes requires additional interpretation.
108 A review of HSG244 ROSOV assessments showed that assessments did not always fully
address the risks in the structured manner required by HSG244, but rather simply asserted that
the provision of ROSOVs was not reasonably practicable. Others did not fully apply the primary
and secondary selection criteria. Of those that did properly follow the steps in HSG244 it was
concluded that:
where the case-specific risk assessment indicated a ROSOV was required where currently only
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manual valves existed, then there was a worthwhile improvement to be gained by fitting a ROSOV;
where the case-specific risk assessment indicated a ROSOV should be provided where
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currently a ROV (which would not fail safe) existed, it was not reasonably practicable to
upgrade to a fail-safe device. But additional risk reduction could be achieved by ensuring that
the cables are fire protected, and a rigorous regime is in place for inspection and testing the
operation of the valves and control systems.