Port Neal Explosion

OVERVIEW
A large explosion at a Port Neal , Iowa, ammonium nitrate fertilizer plant killed 4 employees, injured 18 others, and leveled all buildings and equipment within a 200-foot radius.

PLANT BEFORE THE EXPLOSION	PLANT AFTER THE EXPLOSION

Terra International, the licensee and operator of the neutralizer vessel, and Mississippi Chemical Corporation, the designer of the vessel, contested the cause and responsibility for the incident. A large lawsuit resulted. Both parties retained teams of experts who extensively examined the sparger fragments and other physical evidence to determine whether the explosion initiated inside or outside the sparger. The two teams reached opposite conclusions.

DRAWING OF NEUTRALIZER	PLAN DRAWING OF SPARGER

To resolve this impasse, the judge ordered that an expert metallurgist be appointed on behalf of the court to review the physical evidence and provide an opinion as to the detonation location. Dr. Donald Shockey of SRI International was the chosen expert.

RECOVERED FRAGMENTS	SPARGER FRAGMENT LOCATIONS

The shapes and markings on the sparger fragments provided six important facts about the deformation and failure history of the sparger.
• Large permanent tensile strains were produced in the circumferential direction between the rows of holes.
• Mechanical strain contributed to the thinning of the sparger walls.
• Longitudinal fractures formed the long boundaries of the sparger fragments and occured at roughly 3 o'clock and 9 o'clock locations.
• The pipe walls turned in substantially near the longitudinal fractures on both sides of the sparger.
• Linear markings on the fracture surfaces lay in the radial direction, suggesting that the crack propagated across the pipe wall and not along the axis direction.
• The longitudinal crack surfaces formed a dihedral angle, suggesting that tensile stresses were involved in creating the fractures.

SPARGER FRAGMENT FRACTURE SURFACE

FRACTURE SURFACE DETAILS

The simulation indicated the following sequence of events.

1. External explosion from above caused crimping.	2. Internal explosion initiated shear crack.
3. Shear crack transitioned to tensile crack as top of sparger moves up.	4. Final shape of sparger wall shows dihedral fracture surface, with markings across wall.

The legal case was resolved shortly after the completion of this investigation.

Contact Us
Don Shockey
Director, Center for Fracture Physics
Phone: 650-859-2587
Email: donald.shockey@sri.com