Old man yells at mud

Against the organizers, probably, for organizing a large event with easily foreseeable risks that were not adequately mitigated.

Waivers and disclaimers are not a defense against negligently creating a risky situation.

Note I'm not saying I endorse this, just expecting it to happen based on the history of US civil law.

Pretty sure there's going to be more than a few against the organizers, and maybe the authorities for allowing it to go through despite the forecasts and not getting people out fast enough. Which is ironic considering the general (or at least loudest) philosophy of Burning Man goers is one of laissez-faire techno libertarianism