A Cal/OSHA official confirmed to Eyewitness News on Tuesday it is investigating Covina-based Cleveland Wrecking Co.
That is in addition to an investigation already underway into Lincoln-based Alpha Explosives, which was sub-contracted to handle the implosion, bringing the number of companies the regulator is investigating for the incident to two.
Neither company has returned calls made by Eyewitness News.
The Saturday morning planned implosion of two 45-foot boiler towers off Coffee Road and Rosedale Highway sent debris flying into the air, more than 1,000 feet to the west and east, where spectators were gathered in a shopping center parking lot.
Five people were injured, one critically, when they were hit by flying shrapnel.
Jerry Wood, 43, remains in a Fresno-area hospital after a piece of metal hit his legs.
An initial police report stated his legs had been severed, but family members and a neighbor of Wood said Monday that he had all of his limbs and remained in critical condition.