Safety Third

This is actually the name of an episode of Dirty Jobs. But it’s a title that has stuck with me because it’s near and dear to the sort of things I like to think about. Mike Rowe has a good follow-up article here. The title and show ruffled feathers, but he’s right, it’s an important concept to discuss.

You’ll often hear the mantra “Safety First”. This often means in work places things like wearing fall protection when working at height, or wearing a life vest when working in water, or ear protection, or other safety measures. The idea being that above all else, we have to be safe.

I got thinking about this while reading Rand Simberg’s book, Safe is Not an Option.  He argues that trying to make safety the highest priority of spaceflight is holding us back. I tend to agree.  And I’d like to argue out that despite NASA talking about safety in public announcements, the truth is NASA hasn’t always been upfront about it and also it has made decisions where safety wasn’t first (and I would argue in some cases those decisions were justified).

Now I know at least a few of my readers have read the Rogers Commission Report on the Challenger shuttle disaster.  It’s worth the read, especially Dr. Feynman’s appendix. One of the issues that came up during the investigation was exactly how safe the Shuttle was. (Here I’m referring to the entire system, the orbiter, SRBs and ET). Some at NASA were claiming that the Shuttle had a 1 in 100,000 chance at a loss of an orbiter. (a loss of a an ET or SRB as long as it didn’t impact the Shuttle wasn’t really a concern, as all ETs were lost at the end of each mission and at least 2 SRBs were lost due to other issues). As Feynman pointed out, this meant you could fly the Shuttle every day for 300 years and only have one accident.  What was the reasoning behind such an argument? Honestly, nothing more than wishful thinking.   As we know, the shuttle was far less safe, 1 in 67.5.  That’s a hugely different number.

There were many reasons that lead to either accident and I won’t delve into them here; though I would highly recommend The Challenger Launch Decision by Diane Vaughen as a comprehensive analysis of the decision making that helped lead up to the Challenger disaster.

But let’s talk a bit about how things could have been made safer, but NASA correctly decided NOT to go down that route.  One early iteration of the shuttle design had  additional SRBs mounted to the orbiter that would have been used to abort during an additional 30 seconds of the flight envelope1. I can’t determine if these 30 seconds would have overlapped with the critical 30 seconds Challenger’s final mission. But let’s assume they did. The total cost would have added $300 million to the development of the program and reduced the payload capacity of the orbiter2..

In a system already beset with cost considerations and payload considerations, this might have meant the program never got off the ground literally. Or if it did, it would fail to meet its payload guidelines.  All this for 30 more seconds of additional safety. Would that have been worth it? Arguably not.

Another design decision was to eliminate thrust termination for the SRBs. Again, this is something that would have arguably made the ascent portion of the flight safer: in theory.  The theory being that since you can’t normally shut down the SRBs, you can’t perform an orbiter separation, which means the orbiter can’t detach during the first 2 minutes of the flight and hence can’t perform a return to launch site abort.

But again, adding that safety feature didn’t necessarily make things better. For one thing, it really only would have been useful above a certain altitude since below that altitude all the orbiter could have done is detach from the stack and fallen into the sea with too little time to get into a glide position and make it back to a runway.

But there was a bigger issue: the thrust termination was determined to be violent enough it would probably have damaged the orbiter if used. This could have been mitigated by beefing up the orbiter structure. But this would have imposed an 8,000 lb payload penalty. Since the shuttle was already having trouble reaching its 65,000 lb payload goal, this was determined to be unacceptable3.

So, NASA could have made the decision of “safety first” and ended up with a shuttle system that never would have flown. And given the political calculus at the time, it’s unlikely NASA could have come up with a better solution nor had Congress fund it. The shuttle was an unfortunate compromise brought about a host of factors. But it did fly.

As I like to tie this back to some of my other interests; so what about caving and cave rescue.? I mentioned in a previous post how we’ve moved away from treating one line in the system strictly as a belay line. But what if I told you we often only use one line! There are many places in caving and cave rescue where we do not have a belay line. A good example is for a caver ascending or descending a rope.  This is called Single Rope Technique or SRT. There are some who come to caving from other activities and ask “where’s your belay? You have to have a belay!”

But, a belay line (here used in the sense of catching a caver from a potentially dangerous fall if their mainline fails) is actually far less safe.  I’ll give an example. First let’s start with some possible failure modes

  1. Main rope being cut or damaged to the point of failure
  2. The point the rope is rigged to (the anchor point) failing
  3. Your ascent or descent system failing

So the idea is, if one of those 3 things happen, the belay line will catch you.  But there’s issues with that theory. One major issue is that large drops in caves are often accompanied by air movement and waterfalls. The air movement, or even simple movements by the caver (and influenced by the rope in some cases) can cause a twisting motion. This means that before you know it, your belay line has been twisted around your mainline and you can no longer ascend or descend. You’re stuck. Now combine this with being in a waterfall and you’ve become a high-risk candidate for hypothermia, drowning, and harness hang syndrome.  In other words, your belay line has now increased your chances of dying. So much for the attitude safety first.

Even if you avoid those issues, you haven’t really solved the possible failure modes I listed. If you think about it, anything that’s going to damage your mainline is possible to your belay line. There are some differences, your belay line, for example because it’s moving is far less likely to wear through in a single spot like a mainline might from being bounced on during an ascent. On the other hand it’s more possible to suffer a shock load over a sharp edge if it’s not attended well.

If your mainline anchor point fails, you’re relying on your belay anchor point to be stronger. If it’s stronger, why not use it for your mainline? (there are reasons not to, but this is a question that should cross your mind.)

Finally, for equipment failure, catastrophic failure is rare (only seen in movies honestly) and other failures are better mitigated by proper inspection of your equipment and close attention to proper technique.

Of course the safest thing to do, if we were really putting safety first would to never go caving. But where’s the fun in that.

We can insist on safety first in much of what we do, but if we do, we inhibit ourselves from actually accomplishing the activity and in some cases can actually make things LESS safe by trying to add more safety. And safety is more than simply adding additional pieces to a system. It’s often proper procedures. Rather than adding a belay line, focusing on better rigging and climbing technique for example. Or even simply accepting that sometimes things can go sideways and people may be injured or die.  We live in a dangerous world and while we can make things safer and often should, we should be willing to balance our desire for safety with practicality and the desirability of the goal.

I’m going to end with two quotes from an engineer I respected greatly, Mary Shafer who formerly worked at NASA at what was Dryden Flight Research Center and is now the Armstrong Flight Research Center at Edwards Air Force Base.

Insisting on absolute safety is for people who don’t have the balls to live in the real world.

and

There’s no way to make life perfectly safe; you can’t get out of it alive.

For a more complete record of Mary’s thoughts, I direct you to this post.

Footnotes

    1. Space Shuttle – The First Hundred Missions. Dennis Jenkins, 2001. Page 192
    2. Ibid.
    3. Ibid

One thought on “Safety Third

  1. Pingback: The Soyuz Abort | greenmountainsoftware

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s