Houston, TX (WorkersCompensation.com) - The owner of the largest natural gas pipeline network in North America must rebut claims it caused an explosion at a Mexican plant that killed 22 workers, a federal judge ruled Wednesday. Houston-based Kinder Morgan owns or operates 69,000 miles of natural gas pipelines in North America, including some that run from Texas to a plant in Reynosa, Mexico, an industrial hub on the southern bank of the Rio Grande. The plant is owned by Pemex Exploración y Producción, a subsidiary of Mexico's state oil company Pemex. A gas leak there sparked an explosion on Sept. 18, 2012 that accelerated into a fireball that overtook workers running for their lives, lead plaintiff Javier Alvarez del Castillo said in his fourth amended complaint. "They were engulfed in fire that burnt and singed every inch of skin from their head to their ankles, taking every bit of hair from their head, laying the plaintiffs 'skinless,' like skeletons bare to the bones, with in most cases only their footwear, be it 'Nike,' 'Converse' or work boots, attached to the only portion of their body not reduced to skeleton," the complaint states. Dozens of injured workers and survivors of the deceased sued Pemex, Kinder Morgan and subsidiaries in Harris County Court in September 2014. The case was removed to Federal Court in December 2014. They also sued U.S. companies Emerson Electric Co., Honeywell Analytics and Draeger Safety Inc., who they allege installed faulty operating systems that prevented Pemex from monitoring gas pressure and leaks, or were part of a technical committee Pemex assembled to advise it how to avoid such explosions. U.S. District Judge Keith Ellison on Wednesday dismissed all the claims against Pemex and its subsidiaries. He agreed with Pemex that they are immune under the Foreign Sovereign Immunities Act because they are all owned by the Mexican government. Del Castillo claimed that the "'commercial activity' exception," which can overcome sovereign immunity if "the action is based upon a commercial activity carried on in the United States by the foreign state," applies, since Pemex bought the gas in Texas. Ellison disagreed. "This allegation is insufficient in two critical respects: first, it fails to provide any factual elaboration for the conclusory assertion that the gas purchased in Texas caused the explosion, and, second, it fails to allege that it was the Pemex defendants who purchased the gas," he wrote in a 42-page order. (Emphasis in ruling.) He also dismissed all of del Castillo's claims against the other defendants, leaving only gross negligence and negligence claims against Kinder Morgan intact. "Kinder Morgan and the pipeline defendants were responsible for the initial safety of the natural gas, they were the first line of defense for the workers killed and injured in this explosion," Del Castillo said in the fourth amended complaint. He blamed Kinder Morgan for not adding enough of the odorant methyl mercaptan to the gas before shipping it to Mexico. Natural gas is odorless, so energy companies add the sulfur compound to detect leaks. (Skunk scent is a mercaptan.) "In fact, it is believed the gas lacked odorant," the complaint states. Kinder Morgan also failed to remove water and solids from the gas at its processing plants that moved the gas into Mexico, and the impurities increased the chances of an explosion, del Castillo claimed. Ellison dismissed the negligence per se claim against Kinder Morgan, agreeing with the company that because del Castillo did not tie the allegations to any particular statute or regulation he did not meet the pleading standard. Negligence and gross negligence are easier claims to advance, Ellison wrote, as they require just three elements under Texas law: a duty owed by the defendant to the plaintiff, a breach of that duty, and damages proximately caused by the breach. "A gas company may be liable if facts show that it fails to act reasonably after having notice of defects in the pipes through which gas flows," the ruling states, citing the Texas appellate court case Entex, a Division of NorAm Energy Corp. v. Gonzalez. Though Ellison discarded all the defendants but Kinder Morgan, the impact on the families and workers was not lost on him. "The Court is fully sensitive to the tragedy that is at the heart of this litigation. The injured employees, their families, and the families of the deceased have the Court's utmost sympathy. But, even when — perhaps, especially when — the facts speak of tragedy, the law cannot be made to conform so as to fit the facts," he wrote. Kinder Morgan's attorney James Bettis with Munsch Hardt Kopf & Harr in Houston did not immediately respond to a request for comment Thursday morning.