Final answer:
The question does not provide the correct context for the low-pressure alarm percentage threshold for a gas cylinder. The provided information relates to handling and computation of pressures of high-pressure gas cylinders using the ideal gas law in various situations such as temperature changes and leaks.
Step-by-step explanation:
The low-pressure alarm for a gas cylinder is designed to alert when the capacity reaches a certain threshold. However, from the data provided in the question, it does not specify the exact percentage for the gas cylinder's low-pressure alarm. Instead, the provided information deals with high-pressure gas cylinders and discusses the changes in pressure due to temperature changes, leaks, and what steps can be taken to reduce pressure to a safe level for repairs. These problems are solved using the principles of the ideal gas law, which relates pressure, volume, temperature, and the amount of gas.
For instance, to find the final pressure in a tank after cooling it to dry ice temperature without a phase change, one would use the formula P1/T1 = P2/T2 (assuming constant volume and amount of gas), where P1 and T1 are initial pressure and temperature, and P2 and T2 are final pressure and temperature. Calculations in such scenarios require understanding of gas laws and unit conversions. It is important to read the question carefully and respond to the exact query presented.