The general guideline is: when referring to the quantity represented on the y axis, use . When referring to its unit, use .
However, in this bar chart, the two labels are verbalized in partly same tokens. The actual verbalization is less important than the role in which the words occur.
For example:
the
number of fatal injuries ## quantity on the y axis
increased
to
25 accidents ## unit
There is some inconsistency in the labeling.
Some examples: in 2016
there
were
25
accidents
in 2016
the
number of fatal injuries
increased
to
25