The label was on the other jar
On this page11
The specimen moved and the label did not
Out of the supplier jar, into a classroom jar, with the original label still on the original container. The new jar is unlabelled and holds a material capable of releasing formaldehyde.
The exact words were paraphrased
At the upper tier the label "shall contain the statement May Cause Cancer". A softer phrasing chosen to avoid alarming a class is not the statement the standard names.
The second hazard was left off
The upper tier addresses cancer and respiratory sensitization. A label that mentions only one of those has addressed half of what it is required to.
The tier was assumed from the concentration
The tiers turn on what the material releases, not on the strength of the solution it sits in. Working it out from the recipe is not the same as measuring it.
The cupboard was the exposure
Thirty jars with imperfect seals in an unventilated store, and the eight hour average belongs to whoever works in that room. The limits are airborne and the storage is where the air is.
Only the PEL was checked
Which misses the action level at 0.5 ppm, where duties begin, and the STEL at 2 ppm over fifteen minutes, which is the shape of a dissection lesson.
A home version had no label at all
Because no workplace standard reaches a kitchen. Six months later nobody knows what is in the bottle, which is a worse outcome than the one the standard was written to prevent.
The label lifted
Paper on glass, wiped weekly, in a damp cupboard. An unreadable hazard label is the same as none, and the fix is a label material rather than more text.
The jar was reused for something else
With the old label on it. Which is worse than unlabelled, because now the label is actively wrong.
The fix is a labeling step in the procedure
Whoever transfers, labels, before the jar leaves the bench. One line in a written procedure, and it is the only control that survives staff changes.