The CSB had issued urgent recommendations on the natural gas explosion at Con Agra on June 9,2009. The incident occurred when natural gas lines were being purged free of air using natural gas itself.The CSB urgent recommendations include
(a) Purged fuel gases shall be directly vented to a safe location outdoors, away from personnel and ignition sources
(b) If it is not possible to vent purged gases outdoors, purging gas to the inside of a building shall be allowed only upon approval by the authority having jurisdiction of a documented risk evaluation and hazard control plan.The evaluation and plan shall establish that indoor purging is necessary and that adequate safeguards are in place such as:
• Evacuating nonessential personnel from the vicinity of the purging;
• Providing adequate ventilation to maintain the gas concentration at an established safe level, substantially below the lower explosive limit; and
• Controlling or eliminating potential ignition sources
(c) Combustible gas detectors are used to continuously monitor the gas concentration at appropriate locations in the vicinity where purged gases are released
(d) Personnel are trained about the problems of odor fade and odor fatigue and warned against relying on odor alone for detecting releases of fuel gases
It is not safe in the first place to allow purging of an air filled pipeline with natural gas. You can never control or eliminate all potential ignition sources. PERIOD!!
See the CSB recommendations in this link.
See my latest post on this subject
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