Its only a problem if it leaks! (The C3H6 that is) and there is no wind to disbuse it quickly. And yes it hangs in the low spaces and could easily catch on a spark from something with all those (very hot) motors and pumps everywhere - and the all too casual smoker taking a puff while hiding out round the back where he thinks he is both out of sight and safe...
The methane is very bouyant - so it rises in a plume and very rapidly gets away from any source of ignition and so is less immediately hazardous to those on the ground.
On the cost front - there is the slight cost recovery from selling the produced gas (if possible).
I have some friends who became quite wealthy from building and then selling a small niche oil services company - I even had a chance to participate in the start up but never figured it would catch on as it did. (So it goes!)
Good luck with this (and similar) companies as long as massive fracture stimulated wells are the flavour of the decade all these kinds of things will likely make money - some of them lots of money.