Re: Question about Cyanide Gas (for a good cause :-)

[email removed] (jim vassilakos) writes:

> Subject: Question about Cyanide Gas (for a good cause :-)
> This time I'm
> wondering about cyanide gas (I hope the TML-chemists aren't
> jumpy tonight).

Not at all.  I'm sorryt that I'm late with the answer.  Several people
answered in last night's digest, and gave you the basics of what you need:
The smell, and the notion that the ship filters are probably going to be
capable of removing it as part of the regular air recirculation system.
I agree with this latter, byt the way, when you consider that a likely
contingency to be provided for is a fire onboard, which could give you all
sorts of nasty stuff considering the likely amount of plastic on board a
ship.

> You take NaCN (Sodium Cyanide), mix it with some HCl (Hydrochloric
> acid), and whammo, lots of HCN (Hydrogen Cyanide gas). I means lots.

So far so good.  I assume that you can do the chemical equations and molecular
weights bit enough to figure out that it will take you 49 grams of NaCN plus
36.4 grams of HCl to give you 27 grams of HCN plus byproducts.  Excess acid
would probably be either desirable or OK.

> Enough to really ruin everybody's day assuming you're on a
> closed air supply (like a starship). Say one bucket of
> ingredients per 10,000 tons of displacement affected?

10,000 displacement tons is 135,000 cubic meters.  With my handy copy of
the Army field manual on potential military chemical agents, I see that
they give two example numbers for lethal concentration: At 200 milligrams
per cubic meter of air, the LCt50 is about 2000 mg-min/m**3.  That is, you'd
have to breathe that atmosphere for 10 minutes before you had a 50% chance
of death.  The book says that the lethal dose (figured in minutes in a
given concentration) varies storngly with the concentration because the gas
is detoxified by the body fairly quickly.  At 150mg/m**3, the LCt50 is
4500 mg-min/m**3, i.e. a 30 minute exposure.  OK.  For a rough approximation
let's say that the 2000mg-min/m**3 is a firm figure, and that we want to
deliver the dose in 10 seconds, because at that concentration it will be
instantly detectable and crews must be trained to don vacc suits (or the
helmets) pretty fast in emergencies.  Not to mention the fact that the air
filters would start cleaning it up pretty quickly.  (In fact, they'd
probably keep it confined to the room that the mixing occurred in...but
we'll pretend not in order to get a number).  OK, 10 seconds is 1/6 minute.
So, you need a concentration of about 12000mg/m**3, or 12g/m**3.  135,000
cubic meters would make the total requirement 1620kg.  Each 27g of product
requires  75.4g of starting material, roughly 3:1.  So, you'd need about
4.8 metric tons in order to produce something approaching an instantly lethal
dose over the entire interior of the ship, not counting filter effects,
length of time needed for air circulation, etc...doesn't sound too likely
to me.

> Basically, I need know two things. First, is the above
> description correct? Will just mixing the two make HCN and
> will it really be a gas (ain't much  good as a liquid)?
> And is it really as potent as I'm pretending (one bucket to
> 10,000 tons seems a little steep, maybe it's just me)?

Much too steep.

> Many many many thanks in advance.
>
> [email removed]

No problem.

Rob Dean