That's one reason I blow off any debris from my mower after every use. Actually I do it just to keep it clean, but it would help prevent a fire caused by dry grass build up.
I miss the industrial fire extinguisher service company we had close by.
This was where all the fire departments, commercial and industrial customers had their fire extinguisher needs taken care of.
They had a room full of extinguishers that could not be put back in service, usually due to their age. The guy that ran the place would let me take what ever I wanted for free, these were commercial grade high quality, large capacity extinguishers, not your 5 lb kiddie from Lowes.
I would let my kids practice with them, and have one in every corner of my shop and sheds. Never had one that didn't work, but the company moved a few years ago and some of mine are getting low on the charge gauge now.
oh well, it was great while it lasted.
JB