Mount Sinai was shrouded in smoke, and the smoke was like the smoke of a furnace! And the Mountain exuded greatly because it had become volcanic!
Moses station the people near to an active volcano called Mount Sinai. It was not as active as Mount Etna but still very dangerous. That is why Yehovah said do not let anyone man or animal come near to the mountains, or rather volcano!
When Yehovah came down in the clouds he came down onto an active volcano. And when he called Moses up to this active volcano, Moses became the first volcanologist, but he would not have gone up if Yehovah was not protecting him!
Yet when he came before Yehovah Yehovah was concerned for the safety of the people, because he knew the dangers of a volcano!
Yehovah can change rock into lava, and a mountain into a volcano!