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There is no immediate answer if the FD cannot determine the cause of the fire.
1) If the tenant or a minor in tenant's care causes the fire, the tenant is responsible. If the minor is not the child of the tenant, the actual parent/guardian may also be held liable under F.S.A. § 741.24 if the starting of the fire is proven to have been purpseful by the child.
2) If the fire begins naturally due to the state of the property (lack of normal maintenance, for example), then the tenant is not liable.
3) Normally the parties go off the determination of FD as to who began the fire, which may be argued to be wrong in Court, but generally holds a lot of sway.
4) If the FD cannot determine the cause, then it would be up to the parties to prove in Court as to the cause, if the landlord tries to evict and/or sue for damages. (If so, the landlord has to prove what started the fire).
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