Your hygrometer is probably off... humidity will naturally rise as the chicks begin to hatch.. wet chicks = high humidity
so long as there isn't a fan blowing directly on them then they should hatch just fine (assuming the humidity has been correct during incubation).. IF they start getting stuck in the shells you can assist.. but assisting too early will only cause problems (broken blood vessels and un-absorbed yolk).. so it's best to wait until it's absolutely necessary
also... don't plug vent holes.. they are there to help with fresh air exchange. (fresh air helps prevent carbon dioxide poisoning). For large hatches or for things like goose or emu eggs it's best to make sure there is plenty of fresh air exchange going on..
as the chicks grow in the shell they need more oxygen than a newly set egg.. not enough oxygen = dead chicks
Just think of it this way.. when a hen hatches out her chicks she doesn't run over and dunk her behind in a dish of water to make the humidity rise..
So relax and just observe.. no need to rush in unless there is a serious problem.
yinpu,
I'd like to use your signature line as my FB status. I don't have anything yet- cuz all I can think of are bad words at this point!!!
Pam