The 450 MWh plant is composed out of 210 battery units [1], so a little over 2 MWh just went up in smoke. Sources say that commercial chemistries emit between 20 and 200mg of hydrogen fluoride gas per watt hour. [2] At 100mg/Wh, the pack would have released a fifth of a metric ton of hydrogen fluoride gas onto the neighboring roadway over the course of the fire. You be the judge whether or not that warrants precautions.
Edit: a second pack is on fire, so we're approaching half a metric ton of HF gas now
Not would have, could have released up to 200mg/Wh depending on chemistry, but nothing says 100% of the battery burned.
Anyway, hydrogen fluoride is nasty but well studied. The 5 minute LC 50 for rats was 5120mg/m3 and at 6 hours of exposure 156mg/m3 is lethal for rats. It demonstrates a rapid fall off in toxicity rather than direct bioaccumulation because the damage is from acidification of water in the lungs. https://inis.iaea.org/collection/NCLCollectionStore/_Public/...
Humans exposed to 23mg/m3 notice lung irritation, but short term exposure is considered low risk. By comparison even a short distance from a 2 day fire in 5km/h winds your quickly talking sub 0.1mg/m3. It’s still toxic just not acutely dangerous from lung acidification.
.. assuming that the laptop batteries tested in the paper are a suitable comparison. Tesla’s cells are at least similar LFP chemistry these days, and the documentation [0] lists the same gases in the case of a fire.
But this is not an enclosed space - it’s a fenced-off high voltage switchyard in a paddock more than a kilometre from the nearest dwelling, and this battery hasn’t instantaneously emitted all its contents all at once. It’s also quite a windy and rainy week, which affects how serious a practical hazard this is. The emergency services have notified [1] people within 10km to keep the windows closed nevertheless.
Many more of good people of Geelong have a gigantic oil refinery on their doorstep[2], which is a far greater concern if you want to get exercised about HF-related accidents[3].
Edit: a second pack is on fire, so we're approaching half a metric ton of HF gas now
[1] https://victorianbigbattery.com.au/
[2] https://www.nature.com/articles/s41598-017-09784-z