Dabeaner is correct. If a life is at stake then that takes priority. Of course, there are alternatives to heating than wood or coal fires and these are usually on a thermostat and therefore automatic. Technically, one therefore is not lighting the fire and if its electric heating, then as my article on the Sabbath indicates, that shouldn't be considered fire at all.
The other approach is that the fire is already established and therefore one is merely maintaining the fire and not kindling it.
But when it comes to any of the prohibitions, should their adherence endanger a life, then they are not to be enforced.