What to know about a cold storage warehouse fire in Los Angeles

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Los Angeles firefighters are on their sixth day of battling a fire at a massive warehouse near downtown that stores frozen food.

Smoke has billowed from the warehouse, which was covered in solar panels and insulated like a freezer, filling the air surrounding the roughly 500,000-square-foot (46,451-square-meter) facility.

The blaze that broke out Wednesday has been especially challenging for firefighters due to the nature of the facility operated by Michigan-based Lineage in the Boyle Heights neighborhood east of downtown. Firefighters haven't been able to enter the building and are instead fighting the blaze from outside.

Authorities said a large warehouse fire can typically be put out in a day, but in a cold storage facility, it can take weeks. Los Angeles Fire Department Chief Jaime Moore said there are about 85 million pounds (38.6 million kilograms) of frozen food stored inside.

Here's what to know:

The cause of the fire has not been determined, Lineage said in a statement on its website.

The company, which provides temperature-controlled warehouse space to food and beverage makers, believes the fire began when subcontractors were working on solar panels on the roof, the statement said.

Lineage is working with fire officials investigating the blaze, the statement said.

It will at least take a few more days to extinguish the fire, Los Angeles Fire Department spokesperson Jamie Stewart said.

Fires in cold storage facilities often burn for weeks because their heavily insulated ceilings, roofs and walls make them difficult to extinguish, Stewart said.

Firefighters have not been able to enter the building due to the danger posed by floor-to-ceiling heavy-duty steel rack shelving, he said. They also have been unable to quickly ventilate the roof due to the insulation, which is what they would typically do to release gas and smoke and gain visibility inside a warehouse, he said.

In this case, firefighters have been stripping away exterior walls on certain sides of the building and dousing it with heavy streams of water, he said.

“It is to the point now, with this visibility and the smoke, you can't really assess the safety as far as committing personnel,” Stewart said.

The facility, called Big Bear, stores products such as seafood, pork, beef and poultry before they’re shipped to grocery stores and restaurants on the U.S. West Coast, Lineage said on its website.

A message sent to Lineage seeking details about the food and the companies affected by it was not immediately returned.

Air quality officials said the air around Boyle Heights, a working-class neighborhood, remained very unhealthy Monday and that particulates in the smoke were also affecting the San Gabriel Valley.

The South Coast Air Quality Management District extended a warning about poor air quality until Tuesday afternoon, saying the blaze continues to produce smoke impacting the neighborhood and areas north and east of the fire. The smoke is carrying microscopic particles known as PM2.5 that can penetrate deep into the lungs.

Light winds will also push the smoke in all directions, potentially impacting other parts of metropolitan LA, the district said.

Residents in the most impacted area were told to avoid vigorous physical activity and close all windows, doors and vents, turn off air conditioning and bring people and pets to an inside room because of the risk of hazardous air. Those who need to go outside in the smoky conditions should wear an N95 or P100 mask, health officials said.