ISO 21154:2026

• Abstract:

  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.

• Status: Published
• Publication Date: 26-May-2026
• ICS: 47.020.85 - Cargo spaces
• Technical Committee: ISO/TC 8 - Ships and marine technology
• Drafting Committee: ISO/TC 8 - Ships and marine technology
• Current Stage: 6060 - International Standard published
• Start Date: 27-May-2026
• Due Date: 20-Jun-2026
• Completion Date: 27-May-2026

ISO 21154:2026 is an ISO International Standard for measuring the boil-off-rate (BOR) of cargo containment systems (CCS) on LNG ships. It specifies the principles, test conditions, equipment, data acquisition and processing, and the test report content for LNG carriers, LNG floating storage and regassification units (FSRU), and LNG bunkering vessels. It can also be used as a reference for the fuel containment system (FCS) of LNG fuel ships.

What does ISO 21154:2026 specify?

ISO 21154:2026 specifies how to measure BOR for CCS in LNG ships and how to document the result. The document is organized into clauses 1 to 6, covering scope, references, terms, the measurement principle and facility, the BOR measurement procedure, and the BOR report, plus one informative annex with example tables.

Annex	What it covers
Annex A	Informative examples of the LNG properties record, conditions record, and BOR report tables

The scope focuses on CCS for LNG carriers, FSRU, and LNG bunkering vessels. That makes the standard most useful when a ship project, sea trial, or operational test needs a common way to measure containment performance.

What are the key requirements of ISO 21154:2026?

ISO 21154:2026 measures BOR by tracking the change in LNG quantity over time and calculating loss using a heat balance approach. In practice, the test has to capture both the cargo state and the conditions that influence evaporation, so the result can be compared across voyages and ships.

Measurement data and facility

Clause 4.2 requires recording LNG composition, average liquid and vapour temperatures, LNG quantity, vapour pressure, and at least 10 insulation temperature points. For comparison with estimated BOR, it also records ambient air, external water, void space, voyage conditions, and equipment that affects cargo level such as condensate, reliquification plant, subcooler, spray pump, and vaporizer. This matters because BOR is not just a tank number - it depends on the operating environment and cargo handling equipment.

Clause 4.3 requires automatic recording liquid level, temperature, and pressure devices. The liquid level device must cover 0 % to 100 % loading, the pressure device must meet a stated span accuracy, and the temperature device must meet a stated accuracy tied to its range. That means the test setup has to be instrumented well enough to support repeatable calculations, not just a visual check.

Test conditions and procedure

Clause 5.1 sets the measurement conditions. Wind during the test is limited by Beaufort scale, sea state is recorded in the logbook, CCS vapour pressure must stay constant within the stated tolerance, and the CCS must be in laden condition. For vessels with dual fuel diesel engine or slow-speed diesel engine with reliquification plant, the standard uses a tank-by-tank approach and excludes tanks used for forced vaporization or condensate return. In practice, the test has to reflect normal ship operation while still keeping the conditions controlled.

Clause 5.2 splits the procedure into three phases: after loading, during the voyage at intervals of no less than 6 h, and before unloading. Each phase records the cargo state, temperatures, pressure, composition and density, and insulation temperatures. The procedure also records equipment conditions so extra evaporation or condensation can be accounted for.

Calculation and reporting

Clause 5.4 gives the formulas for BOR and active BOR. The calculation uses correction factors for air, external water, voyage, and equipment conditions, so the reported value reflects the test context rather than raw tank data alone. Clause 6 then requires a BOR report.

What terms does ISO 21154:2026 define?

• Boil-off-rate (BOR) - the percentage of cryogenic liquid lost in 24 h under rated vapour pressure compared with the LNG mass in the CCS at thermal balance and rated filling rate.
• Active boil-off-rate - the same kind of loss ratio, but measured with boil-off gas management equipment used for a specific purpose.
• Liquefied natural gas (LNG) - a cryogenic liquid mainly made of methane, with small amounts of other natural-gas components.
• Cargo containment system (CCS) - the arrangement that contains cargo, including barriers, spaces, and supporting structure where needed.
• Boil-off gas (BOG) - gas generated when LNG naturally evaporates or is forced from liquid to gas by heat absorption or pressure reduction.

Who uses ISO 21154:2026?

ISO 21154:2026 is used by teams that test, verify, or compare CCS performance on LNG carriers, LNG FSRU, and LNG bunkering vessels. It is also relevant to shipowners, because the introduction notes that BOR affects transport cost calculations. Engineers and test personnel use it to plan measurements, collect voyage data, and prepare BOR reports in a consistent way.

Which standards are used with ISO 21154:2026?

Clause 2 states no normative references. The definitions cite ISO 16903:2015 for LNG and the IMO IGC Code for the CCS definition. The bibliography also points to the IMO IGF code and other maritime guidance as related background.

What does the ISO 21154:2026 document contain?

The document contains a measurement principle based on heat balance, a listed set of measurement parameters, and facility requirements for level, pressure, and temperature instrumentation. It also gives a three-phase measurement procedure, calculation formulae for BOR and active BOR, and a reporting clause. Annex A provides example tables for LNG properties, test conditions, and the BOR report, which are useful for trial records and documentation.

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
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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
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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
...