AFAIK dry ice is frozen CO2. So it´s more likely to release this gas. Dry ice should not be touched at all as it´s really cold. Contact with bare skin could cause injuries.

You are right. OOPs on my part

Have pure argon at work just have to think of a creative exuse to "borrow" a cubic foot or so. It is inert like nitrogen, just more expensive.

Visual inspection for sure.

On a couple occasions I've found that the flint from old cigarette lighters (> 5 years) has simply disappeared! Both times they were indoors, no climate extremes. Plus the seal on one jammed open and butane spewed everywhere...

Steve