Everyone speaking English is no guarantee of safety.
That is true, but since the lab was in the US, everyone in it is supposed to have a minimal proficiency in English. In practice, the net result was that the standard procedure was to use English first (allowing others to maintain a good awareness of what was going on around them in the lab), then confirm understanding in another language if necessary.
As a purely safety consideration, it makes a lot of sense to have a lab language. My group right now has 2 PhD students and 3 undergrads, all of whom speak decent to fluent English, and none of whom share another language in common. As it happens in my own lab, I don’t actually care what language people use as long as everyone understands any hazardous conditions that may be present. If I see this not happening as the group grows, I may implement a similar English while setting up experiments rule.
When I began my PhD program, I had never set foot in a tissue culture lab before. I was an engineer, with a wee bit of chemistry experience from my M.S. But if you are intent on growing living cells, you are going to have to autoclave things. Or so I had come to understand.
I was a native English speaker, and so was everyone else in my lab. So, indeed, was everyone else that I interacted with regarding the use of the autoclave. Here’s the extend of the instructions I got about using the autoclave:
“The autoclave is down the hall in room X. Put your stuff in this bin. For glassware you probably want to run it at such-and-so conditions. For liquids you probably want to run it at such-and-so conditions. Don’t forget to put autoclave tape on your stuff so you know after what’s been through the autoclave.”
Everyone spoke English. Yay! But I am pretty sure I ruined some stuff for people, not to mention narrowly missed killing myself, before I finally haphazardly learned how to operate the autoclave.