Penal Code 451, Arson is the crime of intentionally, deliberately and maliciously setting fire to buildings, wildland areas, dumpster, vehicles, or other property with the intent to cause damage. You can also be charged if the fire was caused recklessly. This is called reckless arson under Penal Code 452.
Arson can be charged either as a felony or a misdemeanor.
If you commit arson and accidentally kills someone in the process, you can be charged with murder, under the California "felony-murder" rule.
The most common legal defenses that the fire was an accident, and that there is insufficient evidence to establish Arson.
In order to prove Arson under PC 451, the prosecutor has to show that you intended to do something wrong or to harm someone else on the property. If there is no evidence of such intent, then you may have a good case to reduce the charges down to PC 452, reckless arson.
It is important to contact an attorney to discuss the facts and evidence in order to provide you with the best options.