Collision Avoidance | AIChE

Collision Avoidance

Preventing Process Incidents Caused by Vehicular Impact

Incident Description

A hydrocarbon release and subsequent fire and explosions occurred at the Olefins ll unit at the Formosa Plastics Corporation, USA, Port Comfort, TX, complex. A trailer being towed by a fork lift snagged and pulled a small drain valve out of a strainer in a liquid propylene system, forming a large flammable vapor cloud that subsequently ignited. Operators immediately began to shut the plant down and attempted to isolate the leak. They tried to reach and close manual valves that could stop the release; however, the advancing vapor cloud forced them to retreat. At the same time, control room operators shut off pumps, closed valves, and vented equipment to the flare stack to direct flammables gases away from the fire. Immediately after the release, the vapor ignited creating an explosion. The explosion knocked down several operators and burned two others exiting the unit, one seriously. Flames from the fire reached more than 500 feet in the air. Because of the size of the fire, Formosa initiated a site wide evacuation. Fourteen workers sustained minor injuries including scrapes and smoke inhalation. The extensive damage shut down Olefins ll unit for 5 months. [1]

Lesson Learned:

  • The need for guidance on protecting chemical processes from vehicular impact damage is clear.

Protecting the process from vehicular impact.

The process should be protected from impact by vehicular traffic by administrative controls, location/spacing and impact protection. All three approaches should be considered to adequately protect the process from vehicular damage.

Administrative Controls

Administrative controls to prevent vehicular impact damage to chemical process equipment are important, but they rely on human performance that can be unreliable compared to other types of safeguards. Some examples of administrative controls that can be used to help protect the process from vehicular impact are listed below:

  • Vehicular traffic should be appropriately restricted from areas where pedestrians could be injured or equipment damaged. [2] Such areas should have signs that are clearly visible at the perimeter of the restricted process areas.
  • Safe work permits should be required for operating vehicles in the process area. For example, permits should be required to operate fork lifts, cranes, back hoes, fork trucks and other specialized vehicles. The training required for operating specialized equipment and vehicles should emphasize the need to be aware of equipment containing hazardous materials when operating the vehicles in process areas.
  • Safe driving permits should be required for in plant driving. Training would emphasize the need to be aware of process equipment when driving in the plant and to be aware of process areas where vehicular traffic is prohibited.


  • When designing new plants or modifying existing plants, high traffic areas such as tank car loading and unloading facilities, office buildings and parking lots should be located away from hazardous process areas.
  • Piping systems should be laid out such that the likelihood of them being impacted by vehicular traffic is minimized.  Suggestions to accomplish this include:
    • Providing spacing from piping to the edge of a major plant road – 15 ft. (4.4 m).
    • Providing spacing from piping to the edge of a secondary plant road – 10 ft. (3m).
    • Providing spacing from piping to the edge of a plant access way – 5 ft. (1.5 m).
    • Providing spacing from piping to the edge of the path provided for either access to equipment for maintenance, or to facilitate the removal of such equipment for maintenance, e. g., heat exchanger bundles, large motors, pumps, compressors. – 5 ft. (1.5 m). [3]
    • Locating pipelines carrying flammable (hazardous) fluid underground.[4]

Impact Protection

  • When designing new equipment and piping systems, consider the possibility for impact by vehicles and other equipment in the structural design. For example, some companies require process lines to be a minimum of 1 inch schedule 40 for robustness, because of the vulnerability of smaller line sizes to be damaged by mechanical impact.
  • Impact barriers (pipes) are installed to protect fire protection systems, LP tanks and other process equipment containing hazardous chemicals. Such barriers should be designed specifically for vehicular impact. One design calls for 6 inch diameter schedule 40 pipe set in concrete and filled with concrete that can be slipped into a “socket” pipe of slightly larger diameter that is set in concrete in the ground.[5]
  • To design the proper impact barrier, the following design approach is suggested:
    • Pick the largest expected mass to hit the equipment (truck,crane, etc).
    • Pick the highest expected velocity.
    • Design an array of bollards and concrete anchors that will absorb the energy of the collision. This can be accomplished with individual bollards or bollards of equal size tied together. [6]


[1] “Fire at Formosa Plastics Corporation: Evaluating Process Hazards,” U. S. Chemical Safety and Hazard Investigation Board, Report No. 2006-01-I-TX, June 2006.
[2] Guidelines for Hazard Evaluation, 2nd Edition,” p 404, CCPS, 1992.
[3] Communication from a company not identified.
[4] “Guidelines for Engineering Design for Process Safety,” page 184, CCPS 1993.
[5] Communication from a company not identified
[6] Communication from a company not identified


CCPS wishes to thank John Murphy for authoring this document. We are also grateful to Tim Wagner and Jim Verboon of the Dow Chemical Company, Kelley Keim of Exxon Mobil Chemical Company, Kathy Kas
of Rohm and Haas, Stan Grossell of Process Safety and Design, Henry Febo of Factory Mutual, and John Baik of BP for providing input and peer review guidance.