In Devarim 5:5 Moshe says:
"Because you were afraid of the fire and you didn't go up the mountain..."
It seems that Moshe is saying that the fear of the fire coming from the mountain was why B'nai Yisra'el didn't go up the mountain. But, actually, that is not the reason. They didn't go up the mountain because, G-d told the Moshe to set a border so that the people and animals can't even touch the mountain.
I saw Ramba"n on this verse (View the next page of the link, above to see it.) He seems to imply that there was a time when they had permission to do so. Perhaps, I'm misunderstanding what he's saying. I thought that that there was never permission to approach the mountain.
What is Moshe implying when he connects the fear of the fire with not going up the mountain?