People using Fire pits

Was just wondering what is the story with people using firepits along the canal? I am talking about the people that live between Castleknock and Coolmine and who have gardens that access the canal from Roselawn road.

I was walking down there a day last week and there was a lady burning what looked like off-cuts from trees/branches in her fire pit and there was a guy running in front of me and he let out a roar at her to tell her to stop burning citing that it was illegal. Is it illegal or was it none of his business?