We have a taskforce that handles them. Fire Inspector (me), Police Lieutenant, Property Maintenance Inspector and a Health Department Inspector. In general, we do not force our way inside but talk to them very nicely and you would be surprised that 99% of the time they allow us to come inside. All of us point out items to them and explain options and or items that could be in violation. We will follow-up in 30 days and then every 30-days thereafter if needed and have had pretty good success. There have been a few that have refused us entry and we cannot really do much about them. One thing I do is if it really bad, we will flag them as "No-Go" or "Extreme Hazard" occupancies with our staff and in our dispatch center so our suppression people know it is a hazard and will use extreme caution if the place catches fire.
The Health Department can get a warrant and "force" entry if there is no electric, no water, elderly and/or minors in the house where they believe it poses a health hazard. Once they're in they invite the other taskforce people in as witnesses and experts. We all write violation notices, if necessary, and they are required to comply or the house can be condemned.
All-in-All, like I said, we have had good luck with them. There is one house that we cannot get into that they allegedly were going to try and feature on the hoarding show on Discovery or whatever channel it is, but it has never come to fruition yet.