[chbot] Software and system safety / Therac25 (Re: Drone Delivery Service)

Helmut Walle helmut.walle at gmail.com
Tue Oct 15 10:31:21 BST 2013

All very good points, Charles! Some further comments below...

On 15/10/13 15:44, Charles Manning wrote:
> [...]
> If we have a life saving product that will save 1000 people per year, 
> but it has a bug that will kill 5 people per year then the cautionary 
> approach would be to delay release until we have ironed out the bug 
> that kills 5 people. Meanwhile we are not saving those other 1000 
> people per year, so by withholding the product we are letting people 
> die. Such delays in the name of safety can actually cause more 
> problems than they solve.

Yes, there is a balance to be found here, and modern regulations and 
standards do reflect this very adequately. The concepts used are ALARP 
risks (As Low As Reasonably Practicable), which is a threshold to be 
looked at as part of the risk analysis. And what is considered 
acceptable as ALARP is qualified in the respective standards. For 
medical equipment specifically, there also is the concept of "the 
benefits outweighing the risks".

Example: using a wheelchair is a lot more hazardous than you might think 
when you see a wheelchair. Now wheelchair design is somewhat constrained 
by the need to be able to manoeuvre inside buildings, which usually 
leads to a short vehicle with narrow track width. On top of that, it 
needs to have some height, so that the user can "sit" at the table like 
on a regular chair, and also to be able to reach things. The result is a 
significant tipping risk, and if you are looking at the accident 
statistics you will find that most fatal wheelchair accidents involve 
tipping the vehicle. Restraint systems exist, but are of limited use in 
an open vehicle like this. So these risks are well known, and they are 
consciously accepted, because the mobility benefit people get out of 
these vehicles are so great that a couple hundred fatal accidents 
worldwide per year pale in comparison. This is sad for the people who 
die in these accidents, but basically what we are saying here is a 
reflection on something like "staying in bed is a lot safer than getting 
up and leaving the house" - never mind that if you stayed in bed all day 
you would get decubitus ulcers.

So to summarise this: we are not permitted to make things with 
completely arbitrary risks to the user, by using the cheap excuse that 
nothing in life is perfectly safe. Manufacturers need to analyse risks, 
and assess and evaluate them and come to the honest conclusion that 
their products are acceptable in this regard. And most of them selling 
into well-regulated markets (NZ, AU, EU, US) will do this, because if 
they don't a single incident can be enough for the respective 
authorities to close down their business.

> We see a similar thing happening after Sept 11th when planes were 
> grounded in the interests of public safety and later when people chose 
> not to fly. This lead to more car usage and approx 1500 more car 
> deaths in USA than in the previous or next year.

Yes, this is different, because it is not about making any products. 
It's just a social and administrative response to a one-off incident. 
And we are all just human and as such often act irrationally. 
(Interesting point on the side regarding aviation safety - what is the 
purpose of these buoyancy vests that you find under each seat in 
passenger airliners? One more of these irrational things: if you crash 
into the water hard like AF447 everybody on board is dead before anyone 
could even say "vest"; if you manage a soft landing on water, which is 
technically quite possible, either the water is so cold that you freeze 
to death pretty quickly, or it is warm enough for big sharks... 
Although, maybe I am judging too harshly - did any of the passengers in 
Captain Sullenbergers Hudson River landing benefit from the vests? 

> We get worried about electronics & software failing in a braking 
> system and such, but are less worried about mechanical failures (eg. 
> broken cables) which are far more common.
Yes, and there clearly is a difference between the wider public worrying 
on one side, and how a proper product or system risk analysis is 
performed. Electro-mechanical systems that incorporate a diverse range 
of technologies and parts are required to be analysed at system and 
component levels. And it is understandable to some extent that software 
is subject to intense scrutiny, because it is far less tangible or 
visible than mechanical parts.

> As a species we have a very irrational way of looking at risk, and, 
> back to my main point, lawyers exploit that irrationality to make it 
> really hard to release new products.

Agreed on the human factor's irrationality. Regarding the lawyers, I 
don't know. From my personal experience of working in the areas of 
medical equipment and electrical power supply and control systems, and 
also from taking a look at some whiteware regulations, I have to say 
that we now have some very good and appropriate regulations in these 
areas that also help to get the job done in an organised way. What the 
lawyers then do after a product has been released to the market is a 
different story altogether, and there are huge international 
differences. I know a European bicycle manufacturer that does not export 
any bikes to the US, because the litigation risk just isn't acceptable 
to them from a business point of view.

System and software safety is an interesting topic, and it is highly 
relevant to robotics - if there is further interest in this I could give 
a talk about regulatory frameworks and how they are applied in practice 
sometime, and also present some examples of incidents as case quick case 
studies. It may first sound like a dry topic, but once it is seen in 
relation to people and how they might come to harm and should be 
protected it actually becomes much more interesting. Let me know if 
there is interest in this...

Kind regards,


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