We performed an investigation for a client who had recently had a serious incident. Their wells flow through a sand separator before going through a choke and on to downstream gathering. The sand separator is manually drained through a 2″ choke valve to a 400 bbl atmospheric tank. The well head pressure was around 3,000 psig. The operator tried opening the choke valve to drain the sand separator. Nothing was happening so the operator continued to open the choke valve when suddenly the blockage (probably a hydrate) gave way and about 10-25 MMSCFD of gas through a 2″ line and into the 400 bbl atmospheric tank. The tank’s vent and thief hatch were overwhelmed (estimated capacity of less than 3 MMSCFD) and the tank’s roof of the tank was blown off. Our investigation resulted in many findings and recommendations that made this draining procedure much safer and reliable. A good design can not only be safe, but it can also be more effective and reliable.