I have a weird smell around my back deck, it was present there about a month ago and consumed the house, then it went away and it is back again. It smells like burning although there is nothing that I can see that is smoldering out there and under the deck. It is a strong chemically smell of burning. I cannot figure out what it is and to stop it
It is an old house and there are also gas lines coming right out of the side of the house.

It may be shorting electrical wire. I suggest that you crawl under the deck with flash light and look for the source of smell... Do it in timely manner. Electrical short may cause your house to burn down..

Could it be a gas leak which could cause an explosion. It is possible to hire a meter to find the leak

Any wet spots under the deck? Let me know, Tom