Case Study 5: Sour Water Pipeline Repairs

At a chemical plant, there are two lines carrying "sour water" (water contaminated with hydrocarbons, hydrogen sulfide, or other chemicals). The lines run between the facility's sour water stripping unit and its tank farm where the processed sour water is stored.

A group of maintenance employees is assigned to replace orifice plates in two lines running between the sour water stripping unit and the tank storage farm. One plate is in the line running into the tank storage farm; the other is in the return line. To perform this operation, eleven valves need to be isolated: nine at the sour water stripping unit, and two at the tank storage farm. The tank storage farm is located more than a half-mile from the sour water stripping unit. Because there is no written procedure for this particular operation, the operator issuing the work permit for the orifice plate removals at the sour water stripping unit prepares a supplemental blanking and tagging list in order to identify all energy isolation points. After completing the list, the operator ensures that all nine isolation points within the operational limits of the sour water stripping unit are isolated, blanked, locked, and tagged. Following this step, the two valves at the tank storage farm (the receive and return lines) must be isolated before the lockout/tagout is complete and the permit can be issued.

The sour water stripping unit operator telephones the tank farm operator and requests that both the receive and the return sour water valves be locked out at the tank servicing the sour water stripping unit. The tank farm operator calls back and confirms that lockout is accomplished. No one, however, verified lockout or hung a tag on the two valves at the tank storage farm. The employees took receipt of the permit and commenced work on the orifice plates. Although the tank farm operator indicated he had locked out both of the valves at the tank farm, he had apparently failed to lockout the return sour water valve. Because the line was not isolated at the tank farm, when the employees opened a flange at the site of the orifice plate in the return line, they were exposed to a stream of sour water. An incident report was completed by the employer.

OSHA's investigation discloses that there are no specific procedures for isolating either of the orifice plates, and that a work authorization permit was used. Since the employer has no requirement for retaining blanking and tagging lists once a job is completed, the specific steps taken that led to this incident could not be identified. The work authorization permit form simply had a box checked to indicate that all valves were blocked and locked. The inspection also revealed that the operators of the sour water stripping unit and tank storage farm were trained only to a level of an "affected employee" under the Lockout/Tagout standard.

The employer's lockout/tagout program requires that the permit issuer accompany the permit receiver to the lockout locations listed on the blanking and tagging list and that the receiver verify that lockout is performed by hanging a craft tag on the locked equipment. The permit receiver's lock is then to be attached to the operator's lockbox containing all the keys used to secure the equipment, if applicable.

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