No, Arizona is NOT planning to use Zyklon B for executions
You may have seen an article claiming that Arizona, in an effort to get around difficulties in obtaining chemicals used for lethal injections, is planning to use Zyklon B, the infamous compound used by the Nazis to murder over a million Jews in Auschwitz. When I first heard this, I too was appalled, but I can assure you that while I won't object if you are appalled by executions, you should not think that the State of Arizona is using the same formula the Nazis did.
It is true that Zyklon B contained Hydrogen Cyanide, and it is true that Arizona is planning to use Hydrogen Cyanide, so this article from the Guardian is mostly correct:
However, Zyklon B, like Zyklon A, an earlier iteration, is not just Hydrogen Cyanide. It contained that chemical, plus diatomaceous earth as an adsorbent, and an irritating compound to warn people of the danger. You can see more about that in the Wikipedia article on Zyklon B.
Zyklon B was actually used rather extensively in the US in the pre-WWII era to fumigate freight trains, and clothing. The irritants added are significant, because they make the compound safer for its intended use, by giving a powerful warning if it is accidentally spilled. One of the irritants used, Chloropricin, is sufficiently irritating that it was used during WWI as a tear gas, which while not fatal in itself, caused Allied soldiers to vomit and then remove their gas masks, which allowed the toxic chemicals combined with it to kill them.
Arizona will not be using either an adsorbent, or an irritant, because it will not be using a pesticide. Instead, it will be using Hydrogen Cyanide directly, in the same way as was used in American gas chambers for executions in the 1920s. The Hydrogen Cyanide is actually manufactured on site, as it were, by dropping capsules of Sodium Cyanide into a pail of Sulfuric Acid.
Importantly, Arizona will NOT be adding any irritants such as are present in Zyklon B, because, not to put too fine a point on it, they are not Nazis. I make no representations as to the humanity of execution by Hydrogen Cyanide, but it is surely far more humane than the use of Zyklon B, which created additional agony to the victims of the Holocaust.
While my legal practice did not include Libel Law, it seems to me that alleging that Arizona is proposing a far more horrible method of execution that it actually is, could be libelous.
I began looking into this because I was horrified that anyone could take the Nazi legacy so lightly as to wish to re-implement Auschwitz even on the scale of single executions. My horror changed to anger at being lied to. I suspect that this lie was not intentional, but just another example of social media confusion and amplification.
It is possible that others have overlooked the differences between Zyklon B and Hydrogen Cyanide because they just don't know how horrible Zyklon B as a murder agent is. I studied the Holocaust quite extensively in religious school in the 1970s, but it was not clear to me until today why the victims at Auschwitz were screaming and clawing the doors of the death chambers. After all, Hydrogen Cyanide has an almost pleasant smell, reminiscent of almonds. The truth is that the added irritants, paradoxically used in commerce to make it a safer compound, added to the already unimaginable horror and pain of dying en masse in a crowded "shower".