It is important to make sure that gas supply lines contain nothing but gas before the equipment they feed is started. Unfortunately, there seems to have been little guidance or regulation on how this should be done, and sometimes the pipes are purged (in pipeline work the process is called blowdown) into the interior of a building. With all that gas around just a spark can blow the place up. The U.S. Chemical Safety Board (CSB) cites a number of explosions dating back to 1997 caused by improper purging - practices that were in most cases allowable under prevailing regulations.
One would think that the odorant added to natural gas would warn people when a problem is developing, but this is often unreliable, says the CSB. Senses of smell vary and fatigue, as well as a variety of things can interfere with perception, and new pipes and containers can react with or absorb the odorants in a process called odor fade.
A triggering event
On June 9, 2009 an explosion at a ConAgra Foods Inc. beef jerky plant in Garner, NC killed four people and injured several dozen more, caused severe damage to the building, and resulted in the release of about 18,000 pounds of anhydrous ammonia from broken pipes. Reports indicate that a contractor had attempted to purge air from a gas line that fed a water heater in a pump room by removing a pressure gauge and allowing the gas to vent into the building.
As a result of the ConAgra explosion the U.S. Chemical Safety Board (CSB) on Oct. 2, 2009 released a Safety Bulletin on the dangers of purging gas piping into buildings. CSB Chairman John Bresland pointed out that National Fire Protection Association (NFPA) and International Code Council (ICC) codes "do not require gases to be vented outdoors or define adequate ventilation or hazardous conditions, nor do they require the use of combustible-gas detectors during these operations." He went on to say that the board would release a set of recommendations that these codes be suitably amended.
On Feb. 4, 2010 the CSB released the promised set of urgent recommendations. These urge the NFPA, the American Gas Association (AGA), the ICC and the International Fuel Gas Code Committee to amend their regulations "to require that during the purging of fuel gas piping at industrial, commercial and public facilities:
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 happens again
On Feb. 7, three days after the CSB recommendations were issued, workers were purging natural gas from supply lines at an unfinished Kleen Energy Systems power plant in Middletown, CT. A blast, which was heard and felt for miles, killed five workers (plus one more who died on Feb. 19), injured several dozen more and blew off the sheet metal walls of the plant.
A turf battle?
The CSB quickly announced that it was deploying a team to the site of the explosion. When that team and another from OSHA arrived they were initially denied access, according to local news reports, as local authorities removed key pieces of evidence including security cameras, gas detectors and welding gas cylinders, ostensibly to protect them from an approaching snow storm. The CSB team was subsequently given access, but only under restrictions. The investigation is still under way.
While we still don't know every detail of the Middletown incident, several things are pretty obvious. Regulations may tighten but they may be ignored, and shortcuts in the rush to get a job finished on time are all too common. It's incumbent on all involved to pay attention to safety on the job, to make sure regulations are followed, and to report unsafe conditions before there's a disaster.
What about pipelines?
Blowdowns for maintenance work on natural gas pipeline compressor stations seldom result in explosions, but they do release significant quantities of gas into the atmosphere. Methane, the main constituent of natural gas, is 20 times as effective a greenhouse gas as carbon dioxide, according to the EPA, and it costs money - two good reasons for not blowing it off into the air. The EPA has published a Partner Reported Opportunities (PRO) fact sheet that cites the experience of one company that "has designed new compressor stations with isolation valves positioned in closer proximity to compressors. Due to this design alteration, when the valves are closed, significant lengths of gas-filled piping will not be vented to the atmosphere, thereby reducing methane emissions." The fact sheet estimates a $1000 to $10,000 capital cost and a three to 10-year payback.