The rated flow capacity marked on the pressure-relief devices shall be determined according to
ISO 4126-1:2004 and ISO 4126-7:2004.
Connections to pressure-relief devices
Connections to pressure-relief devices shall be of sufficient size to enable the required discharge to
pass unrestricted to the safety device. No stop-valve shall be installed between the shell and the
pressure-relief devices except when duplicate devices are provided for maintenance or other reasons
and the stop-valves serving the devices actually in use are locked open or the stop-valves are
interlocked so that at least one of the duplicate devices is always operable and capable of meeting the
requirements of 126.96.36.199. There shall be no obstruction in an opening leading to a vent or
pressure-relief device which might restrict or cut-off the flow from the shell to that device. Vents from
the pressure-relief devices, when used, shall deliver the relieved vapour or liquid to the atmosphere in
conditions of minimum back-pressure on the relieving device.
Siting of pressure-relief devices
Each pressure-relief device inlet shall be situated on top of the shell in a position as near the
longitudinal and transverse centre of the shell as reasonably practicable. All pressure relief device
inlets shall under maximum filling conditions be situated in the vapour space of the shell and the
devices shall be so arranged as to ensure that the escaping vapour is discharged unrestrictedly. For
flammable non-refrigerated liquefied gases, the escaping vapour shall be directed away from the shell
in such a manner that it cannot impinge upon the shell. Protective devices which deflect the flow of
vapour are permissible provided the required relief-device capacity is not reduced.
Arrangements shall be made to prevent access to the pressure-relief devices by unauthorized persons
and to protect the devices from damage caused by the portable tank overturning.
Unless a portable tank is intended to be filled by weight it shall be equipped with one or more gauging
devices. Glass level-gauges and gauges made of other fragile material, which are in direct
communication with the contents of the shell shall not be used.
Portable tank supports, frameworks, lifting and tie-down attachments
Portable tanks shall be designed and constructed with a support structure to provide a secure base
during carriage. The forces specified in 188.8.131.52.9 and the safety factor specified in 184.108.40.206.10 shall be
considered in this aspect of the design. Skids, frameworks, cradles or other similar structures are
The combined stresses caused by portable tank mountings (e.g. cradles, frameworks, etc.) and portable
tank lifting and tie-down attachments shall not cause excessive stress in any portion of the shell.
Permanent lifting and tie-down attachments shall be fitted to all portable tanks. Preferably they shall
be fitted to the portable tank supports but may be secured to reinforcing plates located on the shell at
the points of support.
In the design of supports and frameworks the effects of environmental corrosion shall be taken into
Forklift pockets shall be capable of being closed off. The means of closing forklift pockets shall be a
permanent part of the framework or permanently attached to the framework. Single compartment
portable tanks with a length less than 3.65 m need not have closed off forklift pockets provided that:
(a) The shell and all the fittings are well protected from being hit by the forklift blades; and
(b) The distance between the centres of the forklift pockets is at least half of the maximum length
of the portable tank.
When portable tanks are not protected during carriage, according to 220.127.116.11, the shells and service
equipment shall be protected against damage to the shell and service equipment resulting from lateral
or longitudinal impact or overturning. External fittings shall be protected so as to preclude the release
of the shell contents upon impact or overturning of the portable tank on its fittings. Examples of
(a) Protection against lateral impact which may consist of longitudinal bars protecting the shell on
both sides at the level of the median line;
(b) Protection of the portable tank against overturning which may consist of reinforcement rings or
bars fixed across the frame;
(c) Protection against rear impact which may consist of a bumper or frame;
(d) Protection of the shell against damage from impact or overturning by use of an ISO frame in
accordance with ISO 1496-3:1995.