The preponderance of lithium batteries in laptop computers and the 7 billions of phones that are used world wide indicates that that lithium batteries are not extremely prone to fire and are generally safe. If they were extremely dangerous then flying in an airplane with all of the lithium powered devices would be as risky as walking in the Chicago hood on a Saturday night. The biggest risk on a plane is someone getting a phone caught in a seat mechanism and then the battery pinched and breached. That would be bad.
I have installed several gigawatts of battery energy storage systems and have never had any explosive issues with lithium batteries. The battery safety systems keep the risks in check and shut down the system before problems get out of hand. In a battery such as in an EV even if one cell fails the fire stays within that particular battery. The battery enclosures are designed so that the fire doesn't propagate to other batteries within the system.
Thermal runaway has to be forced by over charging or intentionally shorting a cell in a test lab after disengaging the safety features. Those explosions can be spectacular and the gases are toxic, but not anymore toxic than the burning plastics and assorted fluids in any vehicle fire. Dead is dead when it comes to breathing toxic fumes and respirators are required when responding to any car fire.
A lot has been learned over the past ten years and batteries are very much safer than they used to be. Of course that doesn't prevent some fool from designing an EV with the reliability of a Pinto.