The Tracy warehouse fire stretched into its third day on Saturday, prompting officials in the Northern California city to urge smoke-sensitive residents to stay indoors as crews continued their grinding effort to extinguish a massive blaze inside a medical equipment facility.

Air Quality Turns Unhealthy

For residents on the south side of Tracy, a city of roughly 100,000 people, the smoke became more than a nuisance. Air quality on the south side of Tracy, a city of 100,000 people where the Medline warehouse fire has been burning since Thursday, was in the “unhealthy” range, according to air monitors. U.S. News & World Report

The picture had shifted over the course of the week. In the early going, air-quality officials noted that the towering plume was rising high into the atmosphere rather than settling at ground level, which kept readings in the “good” to “moderate” range for a time. By the third day, however, conditions on the south side had deteriorated into the unhealthy zone.

Officials cautioned that the materials burning inside a medical-supply warehouse could release harmful particles, gases, and chemicals, making the smoke a genuine health concern for vulnerable groups even when broader readings looked manageable.

A Long, Difficult Fight

Fire crews aren’t expecting quick relief. Firefighters expected the next few days to remain smoky amid a lengthy effort to put out the fire inside the building, South San Joaquin County Fire Authority Fire Chief Randall Bradley said in a statement. U.S. News & World Report

The scale of the structure helps explain why. The blaze tore through a one-million-square-foot warehouse located about 55 miles east of San Francisco, sending embers flying for miles. Firefighters have been working around the clock, at times in temperatures near 95 degrees, to bring the fire under control.

The cleanup and assessment phase is now underway alongside the suppression work. According to Bradley, the local fire marshal launched an investigation, while officials began meeting with company representatives, structural engineers, and others to evaluate the condition of the building.

Hidden Hazards Inside

Part of what makes this fire especially dangerous lies in what was stored and operating inside. Reports indicated the facility contained hundreds of robots powered by lithium-ion batteries. When those batteries are destroyed by fire, they can produce hydrogen fluoride gas, a toxic byproduct that forced firefighters to rely on specialized breathing equipment while battling the flames.

Despite the hazards, there was a significant piece of good news: all of the warehouse’s roughly 120 employees evacuated safely, and no injuries were reported.

Why the Fire Spread So Fast

A central question in the investigation is why the building’s own defenses failed so badly. Firefighters reported that poorly functioning sprinklers and hydrants with little to no flow seriously hampered their early efforts.

Crucially, officials traced the problem to the facility’s own fire-suppression system rather than the city’s water supply. That distinction matters, and it deepens the mystery, because firefighters noted that an outside company had tested the sprinkler system in January and found no issues at the time.

Compounding the situation, the fire reportedly began on the roof on Thursday afternoon and then spread rapidly, fed by high winds, low humidity, and elevated temperatures that allowed it to extend quickly into the structure.

What Comes Next

For now, residents are being asked to take practical precautions. Officials urged people to avoid the area entirely and warned against touching or moving any debris from the fire. Plans were also being put in place to allow employees to safely retrieve their vehicles from the site.

The consequences may extend well beyond Tracy. Medline is a major supplier of medical-surgical products, including latex gloves, masks, and surgical instruments, and the destruction of a key distribution center has raised concerns about disruptions to hospital supply chains across the western United States.

As the smoke continues to drift and crews press on with a fire that has proven stubborn from the start, the guidance from officials remains straightforward: stay sheltered, stay away from the outdoors near the site, and keep a close watch on local air-quality updates in the days ahead.