Dangerous Goods by Road
Each element intended for the carriage of toxic gases (gases of groups T, TF, TC, TO, TFC and TOC)
shall be fitted with a valve. The manifold for liquefied toxic gases (gases of classification codes 2T,
2TF, 2TC, 2TO, 2TFC and 2TOC) shall be so designed that the elements can be filled separately and
be kept isolated by a valve capable of being sealed. For the carriage of flammable gases (gases of
group F), the elements shall be divided into groups of not more than 3 000 litres each isolated by a
valve.
For filling and discharge openings of the MEGC, two valves in series shall be placed in an accessible
position on each discharge and filling pipe. One of the valves may be a non-return valve. The filling
and discharge devices may be fitted to a manifold. For sections of piping which can be closed at both
ends and where a liquid product can be trapped, a pressure-relief valve shall be provided to prevent
1 For calculation purposes g = 9.81 m/s2.
excessive pressure build-up. The main isolation valves on an MEGC shall be clearly marked to
indicate their directions of closure. Each stop-valve or other means of closure shall be designed and
constructed to withstand a pressure equal to or greater than 1.5 times the test pressure of the MEGC.
All stop-valves with screwed spindles shall close by a clockwise motion of the handwheel. For other
stop-valves, the position (open and closed) and direction of closure shall be clearly indicated. All stopvalves
shall be designed and positioned to prevent unintentional opening. Ductile metals shall be used
in the construction of valves or accessories.
Piping shall be designed, constructed and installed so as to avoid damage due to expansion and
contraction, mechanical shock and vibration. Joints in tubing shall be brazed or have an equally strong
metal union. The melting point of brazing materials shall be no lower than 525 °C. The rated pressure
of the service equipment and of the manifold shall be not less than two thirds of the test pressure of
the elements.
Pressure-relief devices
The elements of MEGCs used for the carriage of UN No. 1013 carbon dioxide and UN No. 1070
nitrous oxide shall be divided into groups of not more than 3 000 litres each isolated by a valve. Each
group shall be fitted with one or more pressure relief devices. If so required by the competent
authority of the country of use, MEGCs for other gases shall be fitted with pressure relief devices as
specified by that competent authority.
When pressure relief devices are fitted, every element or group of elements of an MEGC that can be
isolated shall then be fitted with one or more pressure relief devices. Pressure relief devices shall be of
a type that will resist dynamic forces including liquid surge and shall be designed to prevent the entry
of foreign matter, the leakage of gas and the development of any dangerous excess pressure.
MEGCs used for the carriage of certain non-refrigerated gases identified in portable tank instruction
T50 in 4.2.5.2.6 may have a pressure-relief device as required by the competent authority of the
country of use. Unless an MEGC in dedicated service is fitted with an approved pressure relief device
constructed of materials compatible with the gas carried, such a device shall comprise a frangible disc
preceding a spring-loaded device. The space between the frangible disc and the spring-loaded device
may be equipped with a pressure gauge or a suitable telltale indicator. This arrangement permits the
detection of disc rupture, pinholing or leakage which could cause a malfunction of the pressure relief
device. The frangible disc shall rupture at a nominal pressure 10% above the start-to-discharge
pressure of the spring-loaded device.
In the case of multi-purpose MEGCs used for the carriage of low-pressure liquefied gases, the
pressure-relief devices shall open at a pressure as specified in 6.7.3.7.1 for the gas having the highest
maximum allowable working pressure of the gases allowed to be carried in the MEGC.
Capacity of pressure relief devices
The combined delivery capacity of the pressure relief devices when fitted shall be sufficient that, in
the event of total fire engulfment of the MEGC, the pressure (including accumulation) inside the
elements does not exceed 120% of the set pressure of the pressure relief device. The formula provided
in CGA S-1.2-2003 "Pressure Relief Device Standards - Part 2 - Cargo and Portable Tanks for
Compressed Gases" shall be used to determine the minimum total flow capacity for the system of
pressure relief devices. CGA S-1.1-2003 "Pressure Relief Device Standards - Part 1 - Cylinders for
Compressed Gases" may be used to determine the relief capacity of individual elements. Springloaded
pressure relief devices may be used to achieve the full relief capacity prescribed in the case of
low pressure liquefied gases. In the case of multi-purpose MEGCs, the combined delivery capacity of
the pressure-relief devices shall be taken for the gas which requires the highest delivery capacity of
the gases allowed to be carried in the MEGC.
To determine the total required capacity of the pressure relief devices installed on the elements for the
carriage of liquefied gases, the thermodynamic properties of the gas shall be considered (see, for
example, CGA S-1.2-2003 "Pressure Relief Device Standards - Part 2 - Cargo and Portable Tanks for
Compressed Gases" for low pressure liquefied gases and CGA S-1.1-2003 "Pressure Relief Device
Standards - Part 1 - Cylinders for Compressed Gases" for high pressure liquefied gases).
Marking of pressure-relief devices
Pressure relief devices shall be clearly and permanently marked with the following:
(a) The manufacturer's name and relevant catalogue number;
(b) The set pressure and/or the set temperature;
(c) The date of the last test.
(d) The cross sectional flow areas of the spring loaded pressure-relief devices and frangible discs
in mm².
The rated flow capacity marked on spring loaded pressure relief devices for low pressure liquefied
gases shall be determined according to ISO 4126-1:2004 and ISO 4126-7:2004.