Aluminum cylinders can be damaged by exposure to temperatures greater than 350 °F (177 °C). Exposure to temperatures greater than these, could weaken the cylinder to such an extent that the cylinder could be unsafe to fill. Visual examination of the cylinder is not always sufficient to determine if the cylinder has been heat affected. In most cases, overheating from a fire is readily apparent by standard visual examination. However, other sources of heat (electric element, super-heated steam, hot air) could possibly not produce any visual sign or indicator of overheating. Therefore, a system for indicating if aluminum cylinders have been exposed to elevated temperatures is recommended.
This publication applies to high pressure, seamless refillable aluminum alloy cylinders. While not addressed in this publication, a heat indicating system can also be used on refillable low pressure, aluminum alloy cylinders.