A cargo pallet fire broke out at SFO this afternoon in the United Airlines cargo warehouse yard, sending a plume of black smoke visible from the freeway and temporarily disrupting airport operations.

The fire, which appeared to involve a shipping container on the airport tarmac, was spotted around 2:30 PM near the international terminal. Police moved quickly to close McDonnell Road and shut down the right lanes of northbound 101. The AirTrain — SFO's inter-terminal shuttle — was also taken out of service, leaving travelers scrambling between terminals.

The good news: the fire appeared to be contained to the cargo area and did not involve any aircraft or passenger terminals. As one relieved Bay Area traveler put it, "So glad it's outside, and not a plane."

That's the right instinct. A cargo pallet catching fire is bad. A cargo pallet catching fire next to commercial aircraft full of passengers is a nightmare scenario. By all early accounts, SFO fire crews responded quickly and kept this from escalating.

But let's ask the obvious question: what exactly was in that container, and how did it ignite? Cargo warehouses handle everything from consumer electronics with lithium batteries to industrial chemicals. SFO — and United, whose cargo building this was — owe the public a clear explanation of the cause once the investigation wraps. Airport safety isn't just about TSA lines and runway protocols. It's about the entire operation, including the stuff nobody sees behind the scenes.

For now, travelers heading to or from SFO should expect residual delays, particularly around the 101 corridor and within the terminal loop. Check your flight status and give yourself extra time. The AirTrain outage alone is enough to turn a tight connection into a missed one.

Another commuter summed it up well: "At least it appears contained to that container." Agreed. Let's hope the investigation is just as contained — and that answers come fast.