My chemistry teacher told us how once when he ignited helium in a test tube, the tube broke and he ended up with pieces of glass embedded in his skin. The students had face masks and he was looking the other way "just in case" for this "safe" experiment but he could have easily been blinded.

Things can always go wrong. We probably shouldn't strive for 100% safety because they we'd spend our lives in a padded cell. But we also shouldn't assume things are safe because they're common or routine.