CHARLESTON, SC (WCSC) - The final report on the tarp disaster on the Don Holt bridge this past summer is placing the blame on the nasty weather that developed suddenly that afternoon.
The South Carolina Department of Transportation on Friday released the report on the incident on the I-526 bridge that many now call "Tarpageddon."
The giant tarp fell from the bridge trusses on July 19, trapping and damaging many vehicles, and closing the highway for more than 15 hours.
While investigators could not determine an exact cause, in the executive summary, a chief engineer reports the most probable cause was "…the retention of rainwater from a sudden and unforecasted thunderstorm."
An investigation of the tarp failure was conducted by a licensed engineer with Applied Building Sciences (ABS) hired by the insurance company for Eagle Industrial Painting, the contractor painting the bridge.
The contractor had placed the tarp on the bridge as a containment system for the $9.6 million paint job.
Investigators would not make firm conclusions, saying, "The exact cause of the collapse and sequence of collapse cannot be determined due to the rapid cleanup response."
But they go on to say, "The most probable hypothesis is that the failure was caused by an accumulation of water from an extreme and unexpected thunderstorm."
ABS reports it was the weight of the rainwater on the tarp, and not the wind speeds, that most likely caused the 1" diameter wire rope chokers to fail.
A meteorologist determined that winds reached an estimated 58 miles per hour that afternoon, and 1.68 inches of rainfall was recorded within five miles of the bridge between 5 p.m. and 6 p.m.
The tarp collapsed during rush hour traffic.
The documents released on Friday by the SCDOT show state authorities taking exception to the contractor's claim that the company had applied for a permanent lane closure on the bridge which would have allowed the contractor to remove water from the tarp.
The contractor made a lane closure request in 2016, but the report indicates it was not related to emergency storm preparations.
The SCDOT acknowledged the sudden onset of the storm would not have allowed the contractor to act before the collapse.
The report also notes that multiple calls had been made days before the failure, reporting a loose, blowing tarp.
But according to the Final Review and Findings, the tarp had been secured, and was not a factor in the failure on July 19.
A document from Eagle Industrial Painting and from a preliminary report on the incident states that no hazardous materials fell onto the bridge or in the water.
As for the motorists whose vehicles were damaged during the incident, the report shows that a dozen owners have filed claims with the painting contractor's insurance company, and ten have received payment.
The state agency apologized to drivers, and said the SCDOT is exploring ways to keep this from happening again, including using only a bottom tarp in smaller sections that can be handled in the event of bad weather. The chief engineer says on-site inspectors will review and approve the field installations daily, and the DOT will keep close tabs each day on any tarp changes repairs.