DESIGN CRITERIA FOR AN EXECUTION GAS
Many of the same requirements for the fumigation facility apply to
an execution facility. Generally, however, the execution facility will
be smaller and more efficient. Zyklon B is not recommended for use in an
execution gas chamber generally because of the time it takes to drive the
gas from the inert carrier. Up until now, the only efficient method has
been to generate the gas on-site by chemical reaction of sodium cyanide
and 18% sulfuric acid. Recently, a design for a gas generator has been
completed which will be utilized in the two (2) man gas chamber at the
Missouri State Penitentiary, Jefferson City, Missouri. The author is the
design consultant for this execution gas chamber.
This generator employs an electrically heated water jacket to pre-boil
HCN in a cylindrical vessel. At the time of use, the HCN is already vaporized
and is released through valves into the chamber. A nitrogen burst system
clears the plumbing after use. The total time of the execution is less
than four minutes. The chamber is evacuated at a rate of once every two
minutes for a 15 minute time period, providing some seven (7) complete
The chamber may be of welded steel construction or of plastic PVC.
The doors and windows should be of standard marine watertight construction.
The door is gasketed with a single handle pressure seal. All lighting and
electrical hardware is explosion-proof. The chamber contains the gas distribution
plumbing, the gas generator with the bottle of liquid HCN, electronic heart
monitoring equipment, two (2) seats for the condemned and a gas detector
reading externally, electronically to 10 ppm.
Because the chamber contains so lethal a gas, it is operated at a negative
pressure to guarantee that any leak would be inward. The chamber pressure
is controlled by a vacurizer system which should hold the chamber at a
partial vacuum of 10 pounds per square inch (psi) (operational: 8 psi plus
2 psi of HCN). The negative pressure is maintained utilizing the outward
ambient as a standard. This system is controlled electrically and supported
by a 17.7 cfm displacement vacuum pump. Additionally, a pressure switch
is set to trigger emergency systems if the chamber pressure reaches 12
psi, 3 psi above the operational limit.
The inlet and exhaust system is designed for an air change every two
(2) minutes. The air is supplied by a 2000+ cfm fan on the inlet side of
the chamber and exhausted through the top of the chamber. The inlet and
exhaust valves are both of the inwardly closing type to prevent vacuum
loss and are timed to electrically open in sequence, the exhaust valve
first. This is evacuated through a 40 foot high 13 inch diameter PVC pipe
where the wind disperses the gas harmlessly. The intake air should have
preheat capability to guarantee that no HCN will condense and thereby escape
Gas detectors are utilized for safety. First, in the chamber where
it will electrically prohibit the door from opening until the chamber is
safe, second, outside the chamber in the witness and personnel areas where
they sound alarms and initiate an air exhaust and intake system to protect
the witnesses, as well as, abort the execution and evacuate the chamber.
The safety systems contain warning bells, horns, and lights, as well.
Further, emergency breathing apparatus (air tanks) is available in
the chamber area, as well as, special HCN first aid kits, emergency medical
equipment for HCN and a resuscitator in an adjacent area for medical personnel.
Execution gas chamber design requires the consideration of many complicated
problems. A mistake in any area may, and probably will, cause death or
injury to witnesses or technicians.