What does a plus sign (+) indicate about a gas cylinder?

A plus sign (+) on a gas cylinder indicates that the cylinder can be filled to a maximum service pressure that is 10% above its nominal service pressure. This marking signifies that the cylinder has passed additional testing and is certified to handle higher pressures safely. As a result, it allows for a greater volume of gas to be stored in the cylinder compared to those without the plus sign, which can only be filled to their service pressure.

Understanding this certification is critical for safety and operational efficiency when storing and handling medical gases. It ensures that the filled cylinders can be safely transported and used in applications where a small increase in the volume of gas might be needed. This distinction is particularly important in medical settings where the reliability and availability of gases are crucial for patient care.