The National Transportation Safety Board (NTSB), the agency responsible for investigating transportation accidents in the United States, released updates on three major investigations on June 14.
The NTSB, well known publicly for its involvement in the investigation of aviation incidents which involve harm or loss of human life, is also an agency that oversees the transportation of refined petroleum and gas products, chemicals and minerals. 
The agency determined the cause of a natural gas pipeline explosion that killed six. It also detailed the cause of an accidental release of 204,000 gallons of anhydrous ammonia from a pipeline in an environmentally sensitive area, and released preliminary information involving two commercial aircraft coming within 30-50 feet of each other on a runway.
In the gas explosion disaster, the towing vessel Miss Megan, which was of specifications that did not require inspection by the United States Coast Guard, was being operated in the West Cote Blanche Bay oil field in Louisiana by Central Boat Rentals on behalf of Athena Construction on October 12, 2006. The Miss Megan was pushing barge IBR 234, which was tied along the starboard side of barge Athena 106, en route to a pile-driving location. Athena Construction did not require its crews to pin mooring spuds (vertical steel shafts extending through wells in the bottom of the boat and used for mooring) securely in place on its barges and consequently this had not been done. During the journey, the aft spud on the Athena 106 released from its fully raised position. The spud dropped into the water and struck a submerged, high-pressure natural gas pipeline. The resulting gas released ignited and created a fireball that engulfed the towing vessel and both barges. The master of the towing vessel and four barge workers were killed. The Miss Megan deckhand and one barge worker survived. One barge worker is officially listed as missing.
The NTSB blames Athena Construction for the disaster, citing in the final report that Athena Construction's manual contained no procedures mandating the use of the safety devices on the spud winch except during electrical work. It was found that if the Athena 106 crew had used the steel pins to secure the retracted spuds during their transit, a pin would have prevented the aft spud from accidentally deploying. Furthermore, the spud would have remained locked in its lifted position regardless of whether the winch brake mechanism, the spud's supporting cable, or a piece of connecting hardware had failed.
The NTSB also found that contributing to the accident was the failure of Central Boat Rentals to require, and the Miss Megan master to ensure, that the barge spuds were securely pinned before getting under way. The Board noted that investigators found no evidence that the Miss Megan master or deckhand checked whether the spuds had been properly secured before the tow began. While Central Boat Rentals had a health and safety manual and trained its crews, the written procedures did not specifically warn masters about the need to secure spuds or other barge equipment before navigating. The NTSB stated that the company's crew should have been trained to identify potential safety hazards on vessels under their control.
NTSB Chairman Mark Rosenker said of the investigation's results, "Having more rigorous requirements in place could have prevented this accident from occurring. Not only do these regulations need to be put in place but it is imperative that they are enforced and adhered to."
The NTSB has made a number of safety recommendations as a result of this accident and the subsequent investigation. Recommendations were made to Athena Construction and Central Boat Rentals to develop procedures and train the employees of its barges to use the securing pins to hold spuds safely in place before transiting from one site to another.
The most major of the other recommendations are:
To the Occupational Safety and Health Administration:
To the U. S. Coast Guard
The NTSB also released the result of its investigation into an environmental disaster in Kansas on October 27, 2004 in which 204,000 gallons (4,858 barrels) of anhydrous ammonia was spilled from a ruptured pipeline in Kingman into an environmentally sensitive area. Chemicals from the pipeline entered a nearby stream and killed more than 25,000 fish, including some fish from threatened species.
The incident reached the scale that it did due to operator error after the initial rupture. The 8 5/8-inch diameter steel pipeline, which was operated by Enterprise Products Operating L.P., burst at 11:15 a.m. in an agricultural area about 6 miles east of Kingman, Kansas. A drop in pipeline pressure, indicating abnormal conditions or a possible compromise in pipeline integrity, set off alarms displayed on the computerized pipeline monitoring system. Shortly after the first alarm the pipeline controller, in an attempt to remedy the low pressure, increased the flow of anhydrous ammonia into the affected section of pipeline. A total of 33 minutes elapsed between the time when the first alarm indicated a problem with the pipeline and the initiation of a shutdown.
In its initial report to the {{w|National Response Center|National Response Center|| (NRC), the pipeline operator's accident reporting contractor reported a release of at least 20 gallons of ammonia, telling the NRC that an updated estimate of material released would be reported at a later time. No such report was ever made. Because of the inaccurate report, the arrival of representatives from the Environmental Protection Agency was delayed by a full day, affecting the oversight of the environmental damage mitigation efforts.
The cause of the rupture itself was determined to be a pipe gouge created by heavy equipment damage to the pipeline during construction in 1973 or subsequent excavation activity at an unknown time that initiated metal fatigue cracking and led to the eventual rupture of the pipeline.
"We are very fortunate that such highly toxic chemicals of the size and scope involved in this accident were not released in a populated area," commented Rosenker. "Had this same quantity of ammonia been released near a town or city, the results could have been catastrophic."
As a result of this accident, the NTSB made the following safety recommendations:
To the Pipeline and Hazardous Materials Safety Administration:
To Enterprise Products Operating L.P.:
"The severity of this release of dangerous chemicals into the community could have been prevented," said Rosenker. "The safety recommendations that we have made, if acted upon, will reduce the likelihood of this type of accident happening again."
As well as concluding their investigation of the above accidents, the NTSB also released preliminary information regarding a serious runway incursion at San Francisco International Airport between two commercial aircraft on May 26, 2007.
At about 1:30 p.m. the tower air traffic controller cleared SkyWest Airlines flight 5741, an Embraer 120 arriving from Modesto, California, to land on runway 28R. Forgetting about the arrival airplane, the same controller then cleared Republic Airlines flight 4912, an Embraer 170 departing for Los Angeles, to take off from runway 1L, which intersects runway 28R.
After the SkyWest airliner touched down, the Airport Movement Area Safety System (AMASS) alerted and the air traffic controller transmitted "Hold, Hold, Hold" to the SkyWest flight crew in an attempt to stop the aircraft short of runway 1L. The SkyWest crew applied maximum braking that resulted in the airplane stopping in the middle of runway 1L. As this was occurring, the captain of Republic Airlines flight 4912 took control of the aircraft from the first officer, realized the aircraft was traveling too fast to stop, and initiated an immediate takeoff. According to the crew of SkyWest 5741, the Republic Airlines aircraft overflew theirs by 30 to 50 feet. The Federal Aviation Administration has categorized the incident as an operational error.
The NTSB sent an investigator to San Francisco, who collected radar data, recorded air traffic control communications, and flight crew statements, and interviewed air traffic control personnel prior to the NTSB making the preliminary release.

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NTSB releases updates on status of 3 major US investigations