I use them - I can not smell anything coming off from them when activated. Have used them for yrs while rifle hunting. Have one in my left hand glove and one in my right hand warmer pocket as I usually don;t have a glove on that hand.
Little trick taught to me.
NOTE: FOR SITTING USE ONLY! ( Walk much doing this and your feet are way to hot!
I take the same hand warmer on cold days and activate it. I tape on the siade edges - either side of the hand warmer packet to the top of my toes over my 1st pair of socks. I then put on my second sock and my Sorel Boot on. It will last better than 8 hrs.
But is not for salkers - you will burn up!
I buy in Case lots from Sam's Club and keep them in my truck 24/7.
Far cheaper that way.
JW