all in the household, including adult children residing there or even away at college.  I would not assume there is no damage here.  Pain and suffering can yield damages.  Also, reaction to the pepper spray from an allergic reaction or otherwise can be cited as a form of damage supporting the pain and suffering.  Medical insurers who pay for care are entitled to seek recovery otherwise due their insured for the cost of that care, i.e., the fact the pepper sprayed person got medical care paid for by insurance does not mean the cost of that care can not be charged to a negligent party held responsible for the injury.

I would not want my currently judgment proof kid saddled with a judgment.  It messes up one's credit and threatens any earnings or other acquired assets for ten years, or more if the judgment is renewed, which is a simple process.

There can be liability arising from leaving a dangerous item somewhere from which it can be readily taken and misused.  Pepper spray might not be as dangerous as say a gun, but is considered sufficiently dangerous to be subject to regulation thus making negligent maintenance of it a possible basis for liability.  It isn't the use here that forms the liability, but the leaving it available for others to take, and the foreseeable risk of misuse combined with the risk of harm associated with that misuse. 

Anyway, the significant thing is to contact one's insurance agent to see about coverage.  I would not consult the insurance company until and unless a suit is filed and served as that can serve to raises one's rates.  Also, don't say a darn thing to the injured party, or anyone else if they can help it, as anything you do say can be twisted to come back to haunt you.