Legal Question in Landlord & Tenant Law in New Jersey

That would depend on what the lease says and what caused the fire. The typical lease protects the landlord against such damages unless caused by the landlord. Some leases require the tenants to carry renters insurance which gives the landlord some additional legal protection even if they do not. A tenant with such insurance should look first to their own carrier to pay any damages. The carrier can then collect against anyone else responsible. If a tenant caused the fire, a claim can be made against that tenant but there is always the question of whether any judgment is collectable.

See also: http://info.corbettlaw.net/lawguru.htm