The Cold-Storage Fire and What’s in the Smoke

A 500,000-square-foot Lineage Logistics cold-storage warehouse in Boyle Heights ignited last Wednesday afternoon, reportedly during third-party solar testing on the roof. As of Monday, the Los Angeles Fire Department is in its sixth day of the response. Roughly half the building is still actively burning. Approximately 85 million pounds of frozen food sit inside what is now effectively an enormous, slow-combustion smolder pit.

The South Coast Air Quality Management District has extended a particle-pollution advisory across central Los Angeles County, the San Gabriel Valley, the eastern San Fernando Valley, and northwestern San Bernardino County. Governor Newsom declared a state of emergency on Saturday. Pools, parks, and outdoor youth programs near the fire have been closed.

PCSN’s own PurpleAir feed, refreshed this morning, shows the signature. In the Los Angeles basin, multiple sensors are reading PM2.5 above 50 µg/m³, well into the Unhealthy range. At least one sensor near the plume centerline is reading above 270 µg/m³, which is the Very Unhealthy bracket where everyone, not only sensitive groups, is advised to remain indoors. These are the same exceedances communities in the western corridor see during major wildfire events. The chemistry, however, is not the same.

Why Cold-Storage Smoke Is Not Wildfire Smoke

LAFD Chief Jaime Moore has described the structure as “corrugated steel on the outside walls filled with very, very dense foam,” and noted that “the foam insulation continues to burn slowly once ignited.” The dense insulation that keeps a cold-storage warehouse below freezing for decades is the same material that, once on fire, sustains the smolder for a week.

That foam is almost always polyurethane (PUR) or polyisocyanurate (PIR). When it burns at the low-oxygen temperatures of a deep building fire, the dominant products are not the same as the cellulose-and-lignin smoke that comes off a forest. They include hydrogen cyanide, isocyanates, carbon monoxide, and a heavy load of ultrafine particulate that carries those compounds deep into the lung. The refrigeration system itself was ammonia-based. Lineage has since drained the ammonia tanks and trucked the refrigerant off-site, but the shelter-in-place order issued at ignition was driven by ammonia release, not by particulate.

Public SCAQMD readings have identified bromine and chlorine in trace amounts below health thresholds, and have not flagged significant toxic-metal levels in the plume. That is encouraging. It is also a measurement of what was sampled. Cold-storage warehouse fires are uncommon enough that the public chemistry of their smoke, particularly the long-tail organics produced during a multi-day low-oxygen burn, is not well characterized in the published literature. We do not yet know what we are not measuring.

Why It Matters for the Fire Corridor

PCSN tracks wildland fire in seven western states, and Los Angeles is not on the perimeter map. The reason this event belongs in this journal is that the smoke profile from a modern, foam-insulated, plastic-rich building fire is precisely the smoke profile that increasingly dominates wildland-urban interface events. The January 2025 LA firestorm did not burn brush. It burned houses, garages, batteries, vinyl siding, and the contents of attached structures. The smoke from a WUI fire passing through a built-up neighborhood is closer in chemistry to a warehouse fire than to a forest fire.

That distinction is not academic. Public-health guidance during wildfire smoke events is built on the assumption that the dominant particulate is partially-oxidized organic carbon from vegetation. N95 masks, indoor filtration, and the 24-hour PM2.5 averages used to issue advisories are calibrated to that assumption. They are still useful against structure-fire smoke, but the residual gas-phase load (hydrogen cyanide, isocyanates, polychlorinated and polybrominated organics from electronics and refrigerants) passes through a particulate filter unimpeded.

The takeaway for the corridor is narrow. If you live in a WUI zone where a wildfire will burn through built structures before reaching open country, the air-quality response should not stop at PM2.5. It should include indoor activated-carbon filtration during the event and ventilation discipline for several days after the smoke clears, because off-gassing from contaminated surfaces continues longer than the PurpleAir number says.

What To Do Today

For Los Angeles basin residents: the SCAQMD advisory is in effect at least through Monday afternoon and is likely to extend. If you are in the smoke footprint, stay indoors with the windows closed, run an HVAC system on recirculate with a MERV 13 or higher filter if available, and use a portable HEPA unit if you have one. N95 or P100 respirators are appropriate for outdoor exposure. Children, older adults, and anyone with cardiovascular or respiratory conditions should treat the advisory as binding, not advisory.

For the rest of the corridor: this is the event to use as a planning template for the next WUI fire that runs through a residential subdivision in your county. The Boyle Heights response, the chemistry, the gaps in the chemistry, and the duration of the smolder are the closest analog you will get for free.

Air-quality readings in this article are pulled from PCSN’s daily PurpleAir refresh, available on the air-quality page. The plume footprint is visible on the dashboard map as the high-PM2.5 cluster in the LA basin.