A four-alarm fire at a Santa Clara recycling this afternoon prompted an order for residents to stay inside and close their windows while firefighters put out the blaze.

The fire was reported at ECS Refining at 735 Reed St. in a light industrial section of Santa Clara about noon and black smoke could be seen from the surrounding freeways.

It is the third fire within three years at the facility, which specializes in recycling of plastics and metals and electronics scrap, such as circuit boards, computers, circuits and televisions. ECS also treats waste from photographic industries.

Though the fire is near the Mineta San Jose International Airport, a spokesman said the fire wasn't affecting flights.

Santa Clara Deputy City Manager Carol McCarthy said the county alert system notified people in a rectangular area of Reed, Grant and Lafayette Streets and El Camino Real to shelter in place because of the smoke and plastics at the plant. Santa Clara Fire has called for mutual aid from various cities for help.

"We're all inside, with windows and doors closed. It smells like burning plastic," said Ken Clark of Motorspeed West on Grant Street, an auto repair shop.

"It's right across the street from us," he said. "They store electronics and TV monitors, all stacked all up on pallets, wrapped with Saran wrap. The whole lot is full of them."

"It is their third fire," he said. "They were supposed to be moving before they had another fire."

Some electronics, such as circuit boards, contain mercury, which can bind with oxygen when burned and is potentially dangerous if inhaled.

Such products also contain plastic. When plastic is burned at very high temperatures, in a closed setting, it breaks down cleanly into carbon dioxide and water. But when burned in the open air, the temperature is lower, so the plastic does not break down all the way and toxics can be released into the air. Some burned plastics release carbon monoxide gas; others release benzene, which is carcinogenic. Plastics made of PVC, or polyvinyl chloride, release chlorine gas if burned.

In an October 2007 blaze at the facility, two firefighters and two civilians required medical treatment. That four-alarm fire burned for over three hours and consumed a large debris fire, plastic computers and pallets.

A September 2009 fire caused no injuries but firefighters had to wear special self-contained breathing apparatus to safely douse it. That incident originated in piles of shredded plastic.