Most if not all of the agencies you mention operate on the Palmetto 800 digital trunked radio system. It's the same system that Charleston County and SCHP operate on.
https://www.radioreference.com/apps/db/?sid=5042
Do you have a scanner capable of receiving this system?
If so, the question comes down to which transmission sites are you able to receive from your location? Not all agencies' transmissions are carried on every site. So you have to do some testing and listening to see which sites regularly carry the agencies' transmissions you want to hear.
On the page I linked to above, look at the table called "System Frequencies". Sites 1-10, 1-11 and 1-12 only carry Charleston County agencies' transmissions so you won't hear Dorchester County agencies on those. At Ravenel, you're closest to Site 1-59. I don't know if Dorchester County agencies' transmissions are regularly carried on that site are not. Site 1-18 would most certainly carry the transmissions you're interested in, and site 1-9 might also.
I believe that Dorchester County FD still uses a couple of VHF analog conventional frequencies for tone-out/dispatch, but I'm not sure how much of their operations radio traffic are carried on those frequencies anymore. Nor am I sure if EMS is toned out on either of those frequencies. You won't hear any Dorchester Co Sheriff on conventional frequencies.
Hope that helps.
Brian