You would call 911 in the situation where a small child's palm is burned by hot water.
The other situations seem mild;
a teenager with sunburned arms and is in pain is normal when staying out in the sun for too long,
an older person with a small superficial burn on the leg is a mild case of burn,
and a healthy adult with a burn on the arm from a cigarette is fine (he is healthy and the burn is not extreme).