If the team sent a canary into a tunnel and it returned safely, that means there was no dangerous gas in the tunnel. If the canary did not return, the mining team would not enter the tunnel.
Melting Snow/Ice
If you’re in a wilderness setting, like being on a hike in a national park, it’s best to get to know the immediate dangers of your surroundings before you proceed. If you are at the beginning of the winter, are hiking on a particularly warm day during the wintertime, or you’re out for a hike during a thaw period after the winter has concluded, you should avoid patches of snow and ice for pretty obvious reasons.