Disclaimer: I am not an attorney and this does not constitute, nor should be implied as, legal advice.
You are allowed to use lawful resistance sufficient to prevent the offense if you are about to be injured (or to aid someone else). Resistance sufficient to prevent the offense is the key phrase here. In other words, you can't over-react and kill someone for spray painting your wall, but you are justified in taking the can away, knocking it out of their hand, or even using physical force to arrest them.
Deadly force is never justified over property crime. Deadly force can only be used to stop a threat of death or serious bodily injury. The idea goes that a "less lethal" shot to an arm, hand, etc. can easily miss and warning shots could become unintentional hits or injury a bystander.
So what does one do if someone tries to burn down a building?
If no one is in the building, call the fire department and hope they can get in with a police escort. Engaging rioters who have escalated to arson may result in serious injury or death if you try to stop them. Even though you are justified in attempting to stop (non-lethally) their attack, and if the crowd tries to kill you, shoot at the crowd, your every action might be scrutinized. You also might be overpowered and killed.
If you are in the building, try and leave. Try not to be there in the first place. Fight the fire, not the crowd.
If you cannot leave the building, things become different. Remember, if you use deadly force you will have to articulate why you did what you did in court potentially. What are your other options?
NRS 200.200 Killing in self-defense.
If a person kills another in self-defense, it must appear that:
1. The danger was so urgent and pressing that, in order to save the person’s own life, or to prevent the person from receiving great bodily harm, the killing of the other was absolutely necessary
What will be scrutinized is what seemed reasonable at the time. Could you escape the building? Was the arson a serious attempt to burn down the building, or was the fire so wimpy a kitchen fire extinguisher could have tackled it?
Perhaps you are a business owner who was securing their store against a riot when things flashed over sooner than expected and looters are trying to get inside. You are trying to push a looter out the front door when he pulls a gun and you kill him. The crowd backs off, but now the front and back door is surrounded. Police can't get to you. Let's say someone starts heaving Molotov cocktails through the front window or on the roof. Can you shoot them?
You would likely argue that you were lawfully present in your businesses, were trying to secure it so you didn't need to be there, and you used lawful force trying to shove the first looter out of the hole he created so you could board it up. Only that looter pulled a gun and you killed him in self-defense. Probably no issue there.
You did nothing wrong at this point. You even tried the backdoor, but angry people were banging on that. You were almost just shot, so you are afraid that the angry crowd will beat you to death. The police say they are on their way, but you can't get out until they do.
Not being there isn't an option. Running away isn't an option. Fighting the fire isn't an option. If you shoot arsonists, you are going to have be prepared to argue why deadly force was your only option.
Can you prove that they were trying to burn you alive (or didn't care if in burning down your building, you died in the fire—the felony murder rule is a thing)?
Nevada Carry highly recommends enrolling in a program to protect you from legal costs if you are involved in a self-defense shooting. Join USCCA today!
NRS 200.160 Additional cases of justifiable homicide.
Homicide is also justifiable when committed:
2. In the actual resistance of an attempt to commit a felony upon the slayer, in his or her presence, or upon or in a dwelling, or other place of abode in which the slayer is.
Things might be a little different at home. The NRS is clear that you can used deadly force against anyone trying to break into your home in a violent, riotous, tumultuous or surreptitious manner to attack you. You can shoot that looter/rioter trying to break in because it's highly likely that by entering into an occupied home, his intent is to attack you and commit other felonies.