On Tuesday, April 8, 1997, at approximately 8:59 a.m., a 5,700-gallon hydrochloric acid (HCl) storage tank ruptured during filling. The failure of the HCl tank caused a significant portion of its liquid contents (which totaled about 4,800 gallons of 31% HCl) to suddenly surge over the secondary containment. The force of the liquid also caused a break in the secondary containment wall. Witnesses described seeing greenish-yellow fumes drifting offsite as well as liquid material running offsite and along the street curb to the storm drains. As a consequence of the incident, 8 workers and 32 others were taken to the hospital. A 10-block area, including nearby businesses and residences, was evacuated. Based on the impacts of the incident and the potential for lessons-learned, EPA and OSHA decided to undertake a joint chemical accident investigation to determine the immediate and root causes of the HCl tank failure and to make recommendations to Surpass, government, industry, and others that could assist in preventing similar incidents from occurring in the future. The Joint Chemical Accident Investigation Team (JCAIT) determined that the immediate cause of the incident was the overpressurization of the HCl tank. The team identified the root causes as:
- Modifications to the venting of the HCl tank were not within the tank manufacturer’s specifications for emergency venting.
- No hazard analysis of the modifications to the venting of the HCl tank was performed.
- Inadequate preventive maintenance of the scrubber system.
Additionally, the JCAIT identified the following contributing factor:
- Lack of a written standard operating procedure (SOP) for air off-loading of deliveries to the HCl tank, including an inadequate method for determining that the delivery was complete.
At the facility, workers repackaged 31% HCl onsite in a bottling operation into one-gallon bottles for sale as a treatment for swimming pools. In the spring, the facility typically started receiving HCl shipments more frequently to meet demands for the swim season. Based on production reports for April 1997, the facility repackaged up to 12,000 gallons of HCl April 1 through April 7. Based on purchase order records for 1995 through early 1997, the facility received tank truck deliveries of HCl at an average rate of one to two shipments per month, with some variability due to seasonal demand. During the same period, shipments generally ranged from 4,600 gallons to 5,200 gallons (nominally 5,000-gallon orders) and were ordered from either of two suppliers. In April, the facility had received two deliveries prior to the day of the incident– 5,060 gallons on April 2 and 4,600 gallons on April 4. One of the suppliers was making a delivery of 4,950 gallons on the day of the incident, April 8.
Based on visual observations of the fragmentation of the HCl tank and consideration of the force that would be required to cause the observed damage, the JCAIT determined that the tank failure was due to overpressurization with compressed air rather than to overfilling with liquid. Failure from overpressurization involves a higher energy release than failure from overfilling with liquid, and the damage resulting from the failure of the tank is consistent with higher energy release. In addition, the tank was empty before the delivery of the HCl began and had sufficient capacity to contain the delivery, therefore, overfilling with liquid is unlikely. Given the circumstances of the incident, the JCAIT believes that the failure of the HCl tank was not due to age, wear, or defective materials.
CLICK HERE for the Joint Investigation Report