Generally, any trailer in a trailer park must comply with local laws and the rules and regulations of the park. Smoke detectors are generally required in any residence, which probably includes trailers. Whether the trailer was allowed to be in your particular park would require a review of the laws and rules for your area. The injured man should consult with a local attorney. The park owners should be notifying their insurance company of the incident and the probable claim.
I think you need smoke detectors in any residence you rent by law in California.
My name is Stephen R. Cohen and have practiced since 1974. I practice in Los Angeles and Orange County, CA. These answers do not create an attorney client relationship. My answers may offend I believe in telling the truth, I use common sense as well as the law. Other state's laws may differ.. There are a lot of really good attorneys on this site, I will do limited appearances which are preparation of court documents it is , less expensive. However generally I believe an attorney is better than none.