EAST RUTHERFORD, N.J. — The U.S. Chemical Safety Board (CSB) has released a safety bulletin intended to inform companies that use anhydrous ammonia in bulk refrigeration operations how to avoid a hazard referred to as hydraulic shock. The safety lessons in this bulletin resulted from an investigation into a 2010 ammonia release that occurred at Millard Refrigerated Services Inc., located in Theodore, Alabama.

The accident occurred before 9 a.m. on the morning of Aug. 23, 2010. Two international ships were being loaded when the facility’s refrigeration system experienced hydraulic shock, which is defined as a sudden, localized pressure surge in piping or equipment resulting from a rapid change in the velocity of a flowing liquid. The highest pressures often occur when vapor and liquid ammonia are present in a single line and are disturbed by a sudden change in volume.