Did Banning Lead Cause the D.C. Metro Crash?


tin whiskers

On June 22, a horrific crash between two D.C. Metro trains killed 9 riders and injured more than 70 others. Investigators are still trying to ascertain exactly what failed. Metro Chief John Catoe noted:

What we found during a special review of the data after the accident was that the track circuit periodically lost its ability to detect trains. This is not an issue that would have been easily detectable to controllers in our operations control center. What the analytical profile showed was that the track circuit would fail to detect a train only for a few seconds and then it appeared to be working again.

Over at DC Metblogs, contributor TONIGM speculates about a possible source for the problem—tin whiskers. As he explains: 

When people first started building electric circuits, they used tin metal to solder the interconnections between the copper bits.  It wasn't long before they noticed the tin would get "furry", growing spiky whiskers as the part was used.  These spikes could grow long enough to short out the circuits, and then were so weak that they would break off right after doing so.  A smart metallurgist figured out that adding a small amount of lead to the tin alloy stopped this behavior.

Now, lead is something you definitely don't want in your drinking water (although we D.C. residents enjoyed it for several years). In 2000, European regulators launched a jihad against lead in consumer products. The result, according to TONIGM, was that…

…consumers all over the world were getting lead-free electronics, many times without knowing it.  Many times the same part number started showing up with lead-free solder, making this trend very hard to track.

So yesterday, I dropped a note to one of my expert friends, who agreed with me that the circuitry in the Metro replacement part, more likely than not, contained lead-free solder.  And then, he pointed out the likelihood that the latest Airbus crashes had lead-free solder components in their flight controls.

Could the Metro crash have been causeed by yet another unintended consequence of zealous regulation? We'll see what the investigators determine. 

Go here for whole "tin whiskers" post.