How to Read Gas Cylinder Markings and Labels

A cylinder carries several kinds of information, and each answers a different question. Permanent marks identify the pressure receptacle. The gas label identifies its stated current contents and hazards. Supplier references connect the delivery to quality and commercial records. Read these layers together before accepting a cylinder for use.

The layout varies with the cylinder design, approval system, gas service and destination market. This guide explains the reading sequence. A specific cylinder still needs to be checked against its applicable requirements.

1. Start with the permanent identity

Look for the manufacturer's identity, serial number, construction standard, approval marks, capacity, pressure information and inspection marks. These may be on the shoulder, neck or an approved permanent marking area. Preserve every prefix and unit when recording them. A cropped photograph or one isolated number can change the interpretation.

ISO 13769:2018 covers stamp marking for specified transportable cylinders and tubes, including several cylinder materials and gas services. ISO currently lists the 2018 edition as published, with revision under development. It does not mean that every cylinder worldwide has an identical marking layout.

The serial number identifies the cylinder, not its present gas grade. A supplier barcode may be another identifier, so record both rather than assuming they are interchangeable. Approval marks establish the applicable framework; they do not independently establish today's inspection status or contents.

Water capacity and empty mass are different from gas quantity

Water capacity describes the receptacle's internal volume, commonly in litres. It is not the litres of gas delivered at atmospheric or other reference conditions. A quantity expressed as a standard gas volume also needs its pressure and temperature basis. Our Gas Calculator helps explain those distinctions.

Tare or empty mass requires equal care. Depending on the marking scheme and cylinder type, the stated basis can include or exclude valves, guards, caps and other components. Before using mass difference to establish contents, confirm the applicable definition and weighing configuration with the supplier. A stamped empty-mass value is not automatically the tare for the complete package on your scale.

Working pressure and test pressure have separate roles

Under the refillable UN pressure-receptacle provisions in ADR 2025, section 6.2.2.7.3, PH identifies test pressure and PW identifies working pressure for the specified gas services. Read the complete mark, unit and context. Other approval systems can use different conventions.

Test pressure is not a filling target. Neither a pressure stamp nor an assumed ratio between two pressures provides a filling instruction. The gas, receptacle approval, temperature basis and filling requirements must all be established.

2. Distinguish inspection dates from other dates

A cylinder can carry dates for initial inspection and subsequent periodic inspections, while a label or certificate may show filling, analysis or product expiry dates. They serve different purposes.

BCGA's cylinder-testing guidance, within its UK and ADR context, explains that successful initial and periodic inspections are followed by permanent inspection-date and inspection-body marks. It also describes differing inspection requirements and controlled extensions. There is no universal retest interval that can safely be applied to every cylinder.

Ask the supplier or owner to confirm the current inspection status under the applicable system. A coloured test ring, where used, is a useful visual cue, but unfamiliar or damaged rings require verification. Keep product validity and cylinder inspection status as separate checks.

3. Read the gas label before interpreting colour

The label is the starting point for identifying the stated contents. Check the product name, proper shipping name where applicable, UN number, hazard information and supplier details. A UN number identifies a dangerous-goods transport entry; it is not a purity grade or batch identifier. Use our Dangerous Goods Labels guide alongside the supply documents.

BCGA TIS 6, Revision 4 illustrates typical label information and explains the UK and European colour-code context. Colour is a secondary identification aid. Shoulder and body colours can have different meanings, and supplier practices for mixtures can vary. Do not use a familiar paint colour as proof of contents.

A label also does not establish valve compatibility. Compare the specified connection with the receiving equipment and supply specification. See Gas Packaging Standards, Valves and Threads for that separate check.

4. Match the documents to the physical cylinder

A lot number, fill reference, barcode or QR code can connect the package to the supplier's records. Confirm what each identifier means and which certificate it retrieves. The relevant analytical document may cover an individual cylinder or a defined batch.

For example, Airgas's EPA protocol-gas CoA guidance includes cylinder identification, certified component concentrations, uncertainty and certification dates. That is a specific product framework, not a universal certificate template. Check the agreed specification and the certificate's actual scope.

The OSHA SDS framework links the SDS product identifier to the label and addresses hazards and safety information. Its US requirements are not automatically the rules for every market. Obtain the SDS applicable to your product and destination through the supplier; our Safety Documents page explains its role.

5. Use a practical acceptance checklist

• Record the cylinder serial number and legible approval and inspection marks.
• Match the labelled product and grade to the order and delivery record.
• Check the UN number and hazard information against the supplied documentation.
• Match the cylinder or batch reference to the CoA where one is specified, including relevant validity dates.
• Confirm the SDS product identifier and obtain the applicable version.
• Confirm inspection status, package specification and valve connection with the supplier.

If marks are unreadable, identifiers disagree or a label is missing, keep the cylinder out of routine use under your site's safety arrangements. Ask the supplier or owner for written clarification and the correct records. Do not open or sample an unidentified cylinder to establish its contents.

For procurement, agree the identification and document package alongside Packaging and Quality requirements. A proposed change of contents needs a separate technical assessment; see Changing Gas Service in Cylinders.