Take this for what you will, but I have found that saying things like "you should have" aren't constructive.
Instead, try things like "In the future, take these steps"
Try to help the OP as much as you can out of their predicament, and don't post things that amount to "Well, you shouldn't have put your hand in the fire if you didn't want to get burned"
Going along that analogy, an answer could be phrased more like.
"Well, there isn't much prevention you can do now, except make sure you get medical treatment for that burn. In the future, try approaching the fire with the proper safety equipment, be sure to have an extinguisher nearby, wear fire resistant gloves, try using tools such as a poker, to keep you away from the fire."
See how a difference in tone can help?