It's volcano. They're never 'safe'. They're always unpredictable.
I don't know how many tourists realise that though.
We lived on Big Island, Hawai'i for 3 years. When we arrived, the realtor made a point of telling us about someone she knew who went out to the lava flows, there was a bench collapse, as happens now and then, and it killed her. I don't know if this was a real incident, because a quick google doesn't find it, but people definitely die hiking out near the lava flows and the realtor was probably just warning us as we were quite excited about it all and we had little ones.
Volcanies National Park put out lots of safety information, but there's lots of hazards that aren't immediately obvious besides actual lava/eruptions. Steam explosions, flung rocks, toxic gases. Sulphur dioxide triggering asthma is probably the most frequent problem.
While we were there we hiked across a crater. (Kilauea Iki. There wasn't any lava there back then, obviously. There has been since.) We explored lava tubes. We hiked to the lava flows twice, and stood probably 10-12 feet from flowing lava. We had to cross a couple of miles of old flows to get there. The rangers would mark out a path you were meant to stick to by gluing little flourescent squares to the rock, but there was no guarantee it was safe. When lava cools into rock it tends to form a skin over air pockets so there's a danger of falling through. Saw someone do that; nasty gash on the shin. Could've been worse. They tell you to wear long trousers & good boots, but the basalt is black, if it's sunny it gets very hot, and many people don't bother.
We did not go near where lava was entering the sea. Because they tell you not to do that. People still do.
There were risks to all that. Of low likelihood, but serious consequence. We were pretty aware of them. We took them. If anything had gone wrong, it would've been on us I think.
We also went whale watching.