A 200-foot-high fireball that sounded to many like a bomb ignited in the Williams Olefins plant a year ago Friday from a flammable vapor cloud leaking out of ruptured equipment, killing two, injuring more than 100 people and shutting highways for hours that day.

The next day, Ronald “Rocky” Morris Jr., a longtime and beloved worker at the CF Industries plant in Donaldsonville, was killed and seven others were injured when a piece of contractor’s equipment used to unload nitrogen was over-pressurized and burst, sending out lethal shrapnel.

The back-to-back, unrelated fatal accidents in Ascension Parish a year ago this week sparked soul-searching from area officials and residents who say their well-being is tied to the massive petrochemical sector that lines both sides of the parish’s Mississippi River banks.

“It’s been a trying time in Ascension Parish,” Ascension Parish Sheriff Jeff Wiley told residents in front of CF Industries hours after Morris was killed.

But a year later, driven by low natural gas prices and strong demand, Williams is proposing a new ethane cracker at the complex and, across the Mississippi River, the pile drivers and cranes are already swarming around a new site at CF Industries where a $2.1 billion expansion is underway.

The Williams explosion has shut down the Geismar complex and prompted a series of federal and state probes — including U.S. Occupational Safety and Health Administration findings of serious and willful violations and $99,000 in fines that Williams is contesting — and dozens of lawsuits in Ascension and Iberville parishes. The complex straddles both parishes at the corner of La. 30 and La. 3115.

Williams spokesman Keith Isbell said the company is committed to honoring the memory of the two employees who were killed and has engaged in a massive rebuild, turnaround and expansion of the plant that will improve its safety.

The plant, which is expected to restart operations at the end of the month, and plant processes were the focus of close examination to guide the new improvements and training for employees.

“Safety is our No. 1 priority, and we will only restart the plant when we are certain we can do so safely,” Isbell said.

CF Industries and one of its contractors, Cetco Oilfield Services, were each cited with one serious violation by OSHA and fined in December. Civil suits have focused on Cetco and other CF contractors’ alleged negligence in the incident.

The Williams probes have focused on an idled reboiler, a type of heat exchanger where flammable chemicals are mixed and heated under pressure, that failed catastrophically and may have led to the explosion in the plant’s propylene fractionation unit, where olefins are refined into propylene used in consumer plastics.

New allegations have also emerged this year in the civil suits claiming that Williams officials were warned three times since 2006 by the company’s own safety consultants and an internal audit three months before the blast about equipment settings that may have prevented the explosion.

The reports suggest that a certain type of relief valve on the reboiler that ruptured should have been left open to avoid a major failure, one suit claims.

“Yet, management, over and over, while in Iberville Parish, refused to take basic steps that would prevent the equipment involved in the explosion from over pressurizing,” an amended lawsuit from 76 plaintiffs filed in Iberville Parish on Jan. 2 claims.

The suit cites depositions with company officials, the consultants’ reports and documents allegedly showing the recommendation was up for consideration at annual plant review meetings by executives.

Isbell would not comment on the litigation, but, in legal documents filed in the suit, company officials did not dispute that they received those recommendations but claimed they addressed it in a different manner, rather than keeping the valve open.

Also, the U.S. Chemical Safety Board, whose probe of the Geismar explosion is still ongoing, is looking at two other fires and explosions this spring at two different kinds of Williams’ facilities outside Louisiana.

An explosion and fire broke out at the Williams liquefied natural gas complex near Plymouth, Washington, on March 31, injuring one employee. Then, on April 23, another explosion and fire happened at a Williams gas processing plant in Opal, Wyoming, where no employees were injured, according to Williams statements.

Dan Tillema, the lead Chemical Safety Board investigator of the Geismar explosion, said the agency is looking at those two incidents to see if there are “larger issues” with how the company handles process safety, a major area of focus for OSHA in its probe of the Geismar blast.

“I think we’re looking at those two other incidents just to see if there are larger corporate oversight issues that we should be addressing as far as our Geismar investigation,” Tillema said.

He said while a draft metallurgical report is due in late July or early August, the broader investigative report on the Williams incident is not expected until the end of the year.

Isbell said Williams has conducted its own inquiry into the incident that has been validated by outside experts and is cooperating with the agencies still probing the fire.

“We are near a final agreement with OSHA and are continuing to collaborate with the U.S. Chemical Safety Board,” he said.

CF Industries spokespersons declined comment also this week.

“CF Industries does not wish to address the June 2013 event out of consideration for our employees, the workers who were injured and their families, and, most importantly, the family of Rocky Morris,” said Susan Fisher, company spokeswoman.

Follow David J. Mitchell on Twitter at @NewsieDave.