ISO 21154:2026

International
Standard
ISO 21154
First edition
Ships and marine technology —
2026-05
Boil-off-rate measurement method
for cargo containment system of
LNG ships
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle and facility . 2
4.1 Measurement principle .2
4.2 Measurement parameters .2
4.3 Measurement facility .2
5 BOR measurement procedure . 3
5.1 Measurement conditions .3
5.2 Measurement procedure .4
5.3 Data record .5
5.4 Data posting .6
6 BOR report . 7
Annex A (informative) Examples of record tables . 8
Bibliography .10

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
SC 25, Maritime GHG reduction.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
With the growing international demand for green fuels, LNG has gained widespread use due to its lower
CO emissions, high calorific value and cost-effectiveness. LNG ships, as an important transport equipment,
are increasingly in demand. Central to these vessels is the cargo containment system (CCS), the storage
unit for liquefied gas, which is usually composed of thermal insulation materials and support structures.
Due to the huge temperature difference between ultra-low temperature LNG (−163 °C) and the atmospheric
environment, boil-off is inevitable in the system. The boil-off-rate (BOR) is an important metric for assessing
CCS design quality: the lower the value of BOR, the more efficient and effective the CCS. For shipowners, BOR
also plays a role in calculating transportation costs. Therefore, reliable BOR testing method is essential for
verifying containment system performance at sea.

v
International Standard ISO 21154:2026(en)
Ships and marine technology — Boil-off-rate measurement
method for cargo containment system of LNG ships
1 Scope
This document specifies the principles, conditions, equipment, processes, data acquisition and processing,
and test reports of the boil-off-rate (BOR) test for cargo containment systems (CCS) in liquefied natural gas
(LNG) ships.
It is applicable to the CCS of LNG carriers, LNG floating storage and regassification units (FSRU) and LNG
bunkering vessels. It can be used as reference for the fuel containment system (FCS) of LNG fuel ships.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
boil-off-rate
BOR
percentage between the mass of cryogenic liquid lost during natural evaporation under the rated vapor
pressure in 24 hours and the mass of cryogenic liquid under the effective volume of the cargo containment
systems (3.4) when it reaches the thermal balance at the rated filling rate
3.2
active boil-off-rate
percentage between the mass of cryogenic liquid lost under the rated vapor pressure in 24 hours and the
mass of cryogenic liquid under the effective volume of the cargo containment systems (3.4) with boil off gas
management equipment used for a specific purpose
3.3
liquefied natural gas
LNG
colourless and odourless cryogenic fluid in the liquid state at normal pressure composed predominantly
of methane which can contain minor quantities of ethane, propane, butane, nitrogen, or other components
normally found in natural gas
[SOURCE: ISO 16903:2015, 3.3]
3.4
cargo containment system
CCS
arrangement for containment of cargo including, where fitted, a primary and secondary barrier, associated
and any intervening spaces, and adjacent structure, if necessary, for the support of these elements
Note 1 to entry: If the secondary barrier is part of the hull structure, it may be a boundary of the hold space.
[2]
[SOURCE: IMO IGC Code, 1.2.8, modified — structure of the definition modified to fit the context of this
document.]
4 Principle and facility
4.1 Measurement principle
The rate of change in LNG quantity is measured over time and the loss of LNG during a given period is
calculated based on a heat balance approach.
4.2 Measurement parameters
In order to calculate the BOR, the following parameters shall be measured and recorde
...