TOS is known for being hard on Redshirts. The idea is if you're in security then you're probably not coming back.
But is it really true or just an exaggerated accepted cliche? In GR's TMP novelization he states 94 of the crew died a violent death during the 5-year voyage. Now it's up in the air whether this book can be considered canon, but it certainly doesn't gel with what we saw onscreen.
I just did a quick tally (and anyone feel free to correct me) and this is what I came up with:
(Red) Security personnel: 19
(Red) Support Services: 8
(Blue) Sciences: 3
(Gold) Command: 7
That's the total for the series with the bulk of those happening in the second season. Of those 37 casualties 27 of them are redshirts and 8 of those are Engineering or Support Services. Overall casualties averaged over 3 years = 12.3 deaths per year.
Actually 3 of those deaths happened before the 5-year voyage: Kelso, Mitchell and Dehner. That brings the average down to 11.3 deaths per year.
If we assume this average carried over the remaining two years then we could expect another 22-23 deaths before the end of the voyage. That would mean a total of 57-58 deaths in total during the 5-year voyage. That's quite a few short of the 94 GR states in his TMP novelization.
Now if we accept TAS as the forth year of the voyage then that skews the numbers even more because no Enterprise
casualties occurred throughout TAS. So we have to deduct at least 11 from the total which leaves us with 47 total over five years.
47 casualties over five years is half of what GR states in his book. That's a huge discrepancy. Of 47 we have 19 Security casualties over three years averaging 6.3 per year. With that average (and no deaths seen in TAS) we could expect a total of 25-26 Security casualties over the five years.
It seems to me that perhaps the Redshirt Myth might yet be another exaggerated cliche. Of course, this cliche could have gotten a boost from the bulk of Security casualties in second season: 12. That is effectively double the yearly average and a chunk of those happened in a few episodes: "The Changeling" and "Obsession."