Air releases from an early June fire inside a refrigeration unit at Westlake Chemical Corp.’s vinyls plant in Ascension Parish did not exceed pollution limits and most of what was sent into the sky that day was carbon dioxide, a company estimate says.

Greg Langley, spokesman for the state Department of Environmental Quality, said Tuesday that with that information, the state’s investigation into the fire has been closed.

In a June 11 follow-up report to DEQ, Westlake plant manager James Best wrote that the liquid organic peroxide either came into contact with unspecified “incompatible materials” or reached a temperature that caused a release of flammable vapors, which ignited.

“At this time, we are still investigating the cause of last month’s fire at our Geismar facility,” Dave Hansen, Westlake spokesman, said Tuesday.

Westlake and DEQ officials have said the fire caused no injuries and, based on air monitoring at the time, did not result in off-site impacts.

Plant firefighters spotted and extinguished the 45-minute blaze, which started about 11:15 a.m. June 4 and sent a dark plume of smoke high into the air.

The Westlake report was not available on DEQ’s online records database by early Tuesday evening, but Langley provided The Advocate a copy of the report after a request. DEQ received the report from the Houston-based company June 19.

The refrigerated liquid organic peroxide was used to initiate the production of polyvinyl chloride, a common household plastic made at the plant off La. 30.

Westlake officials have said the peroxide must be refrigerated to keep it from chemically reacting. The new report says the compound becomes highly unstable at temperatures greater than 32 degrees Fahrenheit, the freezing point of fresh water.

In Westlake’s estimate, officials assumed that 95 percent of the 31,340 pounds of organic peroxide in the unit was combusted in the fire. Due to the volatile nature of organic peroxide, Westlake officials assumed the remainder broke down into other compounds.

Of the 9,333 pounds of chemicals ultimately released into the air, Westlake says, an estimated 8,702 pounds were carbon dioxide or argon. Both occur naturally in the atmosphere.

The Westlake estimate says smaller amounts of volatile organic compounds, nitrogen oxides and refrigerants were also released, including butanol, methyl ethyl ketone, 2-ethylhexanol and pentafluoroethane.

Westlake officials said their estimate shows none of the released compounds reached levels that required reporting to state agencies at the time of the fire, but the company reported the release in an abundance of caution.

Westlake officials told DEQ the argon came from 69 storage cylinders burned in the fire.

While 64 of the cylinders were known to contain argon, Westlake officials assumed that the remaining five did also. The fire destroyed all identifying marks showing what was inside the five cylinders, the company report says.

Westlake officials told DEQ in their report that they plan to “implement all necessary measures to prevent a recurrence” of the fire and would provide an update to the agency once the company investigation is finished.

The June 4 fire came one day before Westlake announced several company sites, including the Geismar complex, received safety awards from the Society of Plastics Industry, a trade group.

In March 2012, Westlake’s vinyl chloride monomer unit caught fire and forced state highways and part of the Mississippi River to close.

The U.S. Occupational Safety and Health Administration issued citations and fines for that blaze, which also had no injuries.

OSHA is investigating June 4 incident as well.