Also known as gas expansion rupture or O-ring embolism, explosive decompression is a major risk for any seal operating in a high-pressure gas environment. Gas can get trapped inside the seal’s micropores. If the seal faces an equilibrium shift (as with rapid decompression), this trapped gas rapidly expands in an effort to match external pressure.

The amount of structural damage done to the O-ring as a result of this internal expansion depends on the volume of the trapped gas and the hardness of the seal. Smaller volumes (especially in soft compounds) may only cause surface blisters which can disappear as pressure equalizes. Larger volumes (particularly in hard compounds) can cause deep cross-section ruptures or even total O-ring disintegration. Higher temperatures further aggravate this phenomenon. Figure 131 is an example of O-ring failure due to explosive decompression.

One way to prevent explosive decompression is to allow for longer decompression periods. Trapped gas can exit the elastomer more slowly, minimizing the chances for damage. Use of seal materials in excess of 80 Shore A may also be helpful. Harder, high shear modulus seals have the strength to dissipate fracture energy as it propagates through the O-ring. Smaller cross-sections offer less space in which gas can become trapped.

Generally speaking, carbon dioxide (CO2) is more likely to cause elastomer swell and rupture than nitrogen. For CO2 contact, as in air guns, polyurethane is by far the best choice. For seals facing nitrogen and other pressurized gases, high-ACN content nitrile may be a solution. In some cases, you might consider soaking the seal in specific oils (such as MIL-H-5606) prior to use. The oil fills the spaces that might otherwise be filled by gas.