Fire officials were expected to continue their investigation Tuesday into the cause of a blaze at a Gilbert plumbing-wholesale company that generated thick, black smoke that could be seen for miles Monday.

Gilbert fire Capt. Mark Justus said the midafternoon fire primarily involved materials in a backyard storage area behind Farnsworth Wholesale near Country Club Drive and Baseline Road. No injuries were reported.

Wind whipped the flames and drove the huge plume of smoke for about 90 minutes after the blaze broke out around 3:03 p.m. Flames could be seen shooting up through the smoke, and several small explosions were heard during the first half-hour of the fire.

At least 40 firetrucks and 125 firefighters from Gilbert, Tempe, Chandler and Mesa were on the scene Monday afternoon, and an aerial tanker sprayed water on the fire for about an hour.

As of Monday evening, 27 fire engines and eight ladders were still working the blaze, said Lt. John Lyle of Gilbert police. Gilbert police and fire personnel issued a voluntary evacuation order for those who lived immediately to the east of where the fire broke out. State environmental officials determined by 7 p.m. that it was safe for residents to return, but still advised them to minimize their exposure to the outdoors due to smoke and chemical fumes.

Justus and witnesses said the fire apparently started in plastic piping that lay under the sun, and then it spread to some gas tanks, fiberglass and other building materials.

Farnsworth employee Jim Ramsey said the fire started on the western side of the building and wrapped around the back through wooden structures and cardboard boxes before heading north toward Baseline Road near McQueen Road.

Employees tried to put out the flames with extinguishers, but the fire spread so quickly that everyone was evacuated within five minutes, he said.

Mesa fire Capt. Forrest Smith said firefighters kept the blaze from spreading to buildings by using a defensive strategy, meaning they risked no one's life trying to put out the flames. He said the intense heat is one reason so many firefighters were involved, and crews were rotated to protect their health.

Mike Wood, controller of Farnsworth Wholesale, said he was relieved no one was injured and was making plans to open for business today, using the company's other warehouses in Mesa and Peoria.

He said it is assumed the Gilbert facility will be closed "for many, many months."