What feature is now required in ASME tanks that wasn't mandatory before 1983?

The requirement for an Overfill Prevention Device (OPD) in ASME tanks, which became mandatory after 1983, significantly enhances safety by preventing the overfilling of tanks with liquefied gases, particularly propane. This feature reduces the risk of spills and explosions that can occur due to overfilling. Prior to this regulation, tanks lacked an automatic system to alert users when the tank was full, potentially leading to dangerous situations. Implementing OPDs has been a critical step in increasing the safety standards of storage tanks and ensuring environmental protection.

The other options, while they may be useful in certain contexts, do not reflect the significant regulatory change enacted in 1983 regarding ASME tanks.