From what I can see on the net, it's mainly a problem where people don't recognise the word. Here is some discussion about why people sometimes write トビ主 rather than トピ主 - in this case one possible is that they didn't recognise that the first part is a shortening of トピック and so misread the word originally (apparently it's also easy to hit the wrong key when you're adding dakuten/handakuten on a mobile phone).
I don't think it would be a problem in safety information unless there is some special case where a misreading would cause a dangerous misunderstanding. I can't personally think of one, and the solution would presumably be to rewrite to avoid the potentially confusing vocabulary, rather than increasing the font size.
In terms of displays of safety critical information, that will be defined in a mix of ISO (international), JIS (Japanese), and similar standards, depending on application. For example, here (pdf) is a guideline for the production of the safety notices on consumer electronics, and if you go right to the end there's a list of the appropriate ISO/JIS/etc standards to consult for further info.
On page 19 you can see a summary and then following, some examples. For example, in the first diagram, the top part, where it says 警告{けいこく}, should be minimum 8mm high, the image below, which indicates danger of electric shock, should be larger than the top part, and the explanatory text at the base should be a minimum of 8pt/3mm high, ideally in a gothic font. There are also guidelines for how to write the text (simple sentences of 40 characters or less, no technical jargon, etc).
