There are pros and cons to each type of seal and situations where dry seals are desired over wet seals and wet seals are favored over dry-running models. Wet seals are preferred where dangerous chemicals are involved in the process. The reason is that if the seal fails, the vapors will be trapped in the barrier fluid and will have little chance of entering the atmosphere. With a dry seal the vapors have a better chance of escaping. Typically wet seals have a better life expectancy. A major disadvantage when using wet seals is the potential for barrier fluid to enter the process and possibly contaminate the batch. This is a huge factor for pharmaceutical applications and other processes that have stringent demands for product purity. Therefore, dry seals are preferred where contamination of the process is a priority. Dry seals require less maintenance than wet seals because there is no lubricator to maintain and refill when the level is low. With face seals nitrogen leaks into the vessel and some carbon dust from the carbon faces will enter the process. The OptiSeal is the only seal where only nitrogen and possibly a miniscule amount of PTFE enter the vessel.