AS 3961:2017 The storage and handling of liquefied natural gas
2.3.3 Discharge from relief devices
The location of the discharge point and the direction of discharge from a safety valve or other pressure-relief device shall be such that hazards from venting vapours are minimized. Vapour impingement on tanks or piping shall be prevented. The direction of discharge shall be vertically upwards except where another direction is necessary to comply with this Clause, e.g. to avoid impingement. A safety valve and any associated discharge piping shall comply with the following requirements when installed:
(a) The size of any discharge piping shall be sufficient to ensure that the required discharge capacity of the safety valve is achieved. Refer to AS 1271.
(b) Irrespective of any provisions for recycling vapour discharges from pressure-relief and pressure control devices, the design shall ensure that the required discharge capacity of a safety valve will be released without restriction in an emergency.
(c) The outlet shall not be vulnerable to physical damage.
(d) Provision shall be made to prevent the accumulation of rain, dew, or foreign matter within the safety valve in such a manner as to cause backpressure or render the valve defective. For pressure tanks, the point of discharge shall have a self-closing device designed so that no parts become separated if a discharge occurs. Where a weep hole or drain is provided in order to comply with this requirement, the overall design shall be such that any ignited discharge cannot impinge on the tank, adjacent tanks, piping, or equipment. A deflector or a drainage discharge pipe may be provided; any such piping shall not incorporate a valve.
2.4.1 Reserve instrumentation
Where it is not acceptable to operate without continuously functioning instrumentation, so that alternative instrumentation is provided, any provision for isolating one instrument for service shall be such as to ensure that the alternative instrumentation is not also isolated at the same time.