Pressure increase inside enclosures can be caused by which of the following?

• A. The process could generate gaseous reaction products
• B. Liquids in the process could be vaporized by the heat of the reaction
• C. A vent or other pressure release mechanism could fail
• D. All of the above

Answer: (D)

Pressure inside an enclosure rises when there are more gas molecules present, when heat drives liquids to vaporize, or when there is a failure to relieve pressure. If a reaction generates gaseous products, the amount of gas in a fixed-volume space increases, so the pressure goes up (P increases with more moles of gas at a given temperature and volume). Heat from the reaction can cause liquids in the system to vaporize, adding additional gas to the headspace and raising the pressure further. If the vent or other pressure-relief mechanism fails, that built-up gas cannot escape, allowing pressure to continue to rise until the system ruptures or a relief occurs. Each pathway can contribute to pressure rise on its own, and they can act together, so the option that includes all of these is the best answer.