The forcefields protect the alien lord in the classic version of spelunky, but in the HD version it protects the alien queen. Since I do not own the HD version, that is all I know of forcefields. Other than the fact more than two protect the alien lord in the classic.
Sorry if I'm overworking you, TenhGrey.
Thanks bro the old spelunky was epic but i highly recomend getting the hd version it is well worth it