Lessons Learned Issued in 2001
Over/Under Pressure Relief Required for System Safety

Date: May 1, 2001

Identifier: 2001-RL-HNF-0018

Lessons Learned Statement:
Systems can be seriously damaged when over or under pressurized without adequate pressure/vacuum relief protection.  Such system failures can cause serious injury or death.

Discussion of Activities:
The three events described below demonstrate the need for ensuring that systems are adequately designed and that their pressures are controlled within design parameters.

Incident #1:

The general-purpose tank car in the photo below was being steam cleaned in preparation for maintenance.  The job was still in progress at the end of the shift so the employee cleaning the car decided to block in the steam.  The car had no vacuum relief so as it cooled, the steam condensed and the car imploded.

 Incident #2:

Workers were purging a two-mile pipeline between an oil and gas well and a Louisiana separation facility when a third-stage separator vessel ruptured due to overpressurization, releasing flammable material, which then ignited.  Natural gas from the ruptured vessel produced a large fireball, which damaged nearby piping, releasing and igniting additional flammable materials.  Four workers who were near the vessel when it failed died instantly from massive trauma.  The separator vessel was not equipped with a pressure-relief device

 Incident #3:

The outflow valves on a KC-135 aircraft, which are used to regulate the pressure of the aircraft, were capped off during a 5-year overhaul and, for some reason, were not reopened.  A civilian depot technician subsequently performed a pressure check on the aircraft with a homemade gauge and without a procedure.  The gauge didn't have a maximum peg for the needle so the technician did not see the needle go around the gauge the first time.  As the technician continued to pressurize the aircraft with the needle on its second trip around the gauge, the aircraft exploded, blowing the rear hatch over 70 yards!  Fortunately, no one was injured.

Analysis:
Closed systems must be adequately vented or provided with over/under pressure relief devices when performing maintenance that can affect pressure in them.  System designers must consider likely pressure excursions when calculating relief set points and flow capacities.  Work that disables relief protection must be planned and conducted very carefully, and should, if possible, provide alternate pressure/vacuum relief devices while the primary device is disabled.  Positive checks should be included in work instructions to restore the primary relief devices to operation when the work is finished.

In the first incident, workers subjected the tank car to external pressure that it was not designed to withstand.

In the second incident, an effective formal engineering design review process should have been in place during the design of the facility.  That process would likely have identified the danger of catastrophic overpressurization of the third-stage separator and indicated the need for a pressure-relief system.

The third incident reinforces the need to be sure we have trained people, who have the right tools, and who follow procedures.

Recommended actions:
Review these incidents with pressure system designers and those responsible for preparing maintenance instructions on pressure systems.

Estimated Savings/Cost Avoidance: N/A

Priority Descriptor: BLUE/Information

Work / Function:  Conduct of Operations - Work Planning; Engineering and Design - Non-Nuclear; Inspection and Testing; Maintenance - Mechanical

Hanford-Defined Category: N/A

Hazard(s): Pressurized Systems

ISM Core Function(s): Analyze Hazards

Originator: Fluor Hanford, Inc.

Contact: Project Hanford Lessons Learned Coordinator; (509) 373-7664; FAX 376-6112; e-mail: PHMC_Lessons_Learned@rl.gov

Authorized Derivative Classifier: Not required

Reviewing Official: John Bickford

Keywords: tank, pressure vessel, vacuum, over pressure protection

References: CSB Final Report on Fatal Louisiana Catastrophic Vessel Failure (http://www.csb.gov/index.cfm?folder=news_releases&page=news&NEWS_ID=50.)