It can turn out pretty bad if people just see it as an opportunity to get an easy job because of lowered standards. A firefighter's job is not necessarily the same as some guy working a non-physical job, where they don't have to face life-threatening situations.
Anything other than employing people based on the quality of their performance, might lead to an institution that's not being as effective as it should be. And in the case of an institution like this, we're talking about people's lives at stake. If we look at some less developed countries in the world, people hiring based on tribe, nepotism, religion, ethnicity, these sorts of hiring practises usually lead to corrupt and inefficient institutions, which endanger people's lives. People collecting checks and doing the bare minimum for service.
The way I see it, if the government wants to increase the amount of women and minority representations in such institutions, then you have to go for a cultural campaign which promotes fire-fighting among these groups. And if the numbers still don't improve then it probably just means that those groups don't care about the job, they don't feel motivated by it. And who could blame them? It's not like a fire-fighter makes a lot of money compared to the sacrifices they make. It is, in many ways a high risk/low reward job, geared towards "thrill-seekers" and physical people.
If it's just a matter of hiring women and minorities for representation, then what sort of a representation are we going to end up with? People who are most likely going to have less skills and less motivation on average than others, because of the lowered standards. This is not the kind of representation that people should want.