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From: TSS (
Subject: Use of containment pans and lids for autoclaving caustic solutions
Date: October 21, 2004 at 4:01 pm PST

-------- Original Message --------
Subject: Use of containment pans and lids for autoclaving caustic solutions
Date: Thu, 21 Oct 2004 17:06:26 -0500
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy

##################### Bovine Spongiform Encephalopathy #####################

Use of containment pans and lids
for autoclaving caustic solutions

Stanley A. Brown, DEng(a)
Katharine Merritt, Ph.D.(b)
Rockville, Maryland

As a means of decontaminating instruments possibly exposed to
Creutzfeldt-Jakob disease, the World Health Organization
has recommended immersion and autoclaving in sodium hydroxide.
However, this recommendation has raised concerns
of possible damage to autoclaves, and hazards to operators as
a result of the caustic vapors. A series of experiments has
been conducted that demonstrate that there are containment
pan-and-lid combinations in which instruments can be auto-
claved in sodium hydroxide without risk to the autoclave or
the operator. (AmJ Infect Control 2003:31:257-60.)

The transmissible spongiform encephalopathies
comprise a group of diseases that include
Creutzfeldt-Jakob disease in human beings, bovine
spongiform encephalopathy (mad cow disease) in
cattle, and scrapie in sheep.1 The infectious agents
(prions) found in these diseases are very difficult to
destroy. They are not completely inactivated by
conventional sterilization methods such as steam
autoclaving, even at increased temperatures, or by
ethylene oxide gas.2-6 Incubation time after infec-
tion may be a matter of years. Transmission of
Creutzfeldt-Jakob disease in human beings and ani-
mals by contaminated instruments has been
demonstrated, but the devices were not subjected to
modern cleaning, disinfection, and sterilization
methods.7-9 In the absence of any scientific study
demonstrating successful decontamination, there is
a growing public health concern regarding the
spread of the disease by potentially contaminated
surgical or dental instruments subjected to standard
hospital cleaning and sterilization protocols.

The World Health Organization (WHO)2 and the
Centers for Disease Control and Prevention3 recom-
mend that before cleaning, terminal sterilization,
and reuse, instruments should undergo one of sev-
eral severe decontamination protocols if they have
been used on patients with suspected or confirmed
Creutzfeldt-Jakob disease. The most highly recom-
mended protocol is to: "immerse (the instruments)
in 1 N (3.9%) sodium hydroxide (NaOH) and heat in
a gravity displacement autoclave at 121°C for 30
minutes, clean, rinse in water, and subject to rou-
tine sterilization."2,3

Autoclaving involves high pressure with steam to
attain high temperatures. There is condensate for-
mation during the cycle and hazardous substances
such as NaOH condensate in the autoclave could
cause corrosion. Some sterilizer manufacturers
have stated that this will void their warranty. The
objective of this study was to determine whether,
with the appropriate containment pans and lids, it
was possible to autoclave NaOH without high pH
condensate contacting the autoclave.


The initial objective of this investigation was to
focus our attention on lid and pan designs. The
classification scheme shown in Fig 1 was developed
to help describe different designs that might con-
tain the caustic vapors. Rather than attempt an
exhaustive study of these 6 combinations, it was
decided to test 2 combinations that showed
promise of containing the caustic vapors. Both
designs selected were made of polypropylene,
which is known to be very resistant to autoclave
temperatures and NaOH.

>From the Divisions of Mechanics and Materials Science,a and Life
Sciences,b Office of Science and Technology, Center for Devices and
Radiological Health, Food and Drug Administration.

The mention of commercial products, their source, or their use in
connection with material reported herein is not to be construed as
either an actual or implied endorsement of such products by the US
Food and Drug Administration.

Reprint requests: Stanley A. Brown, DEng, Division of Mechanics and
Materials Science, Office of Science and Technology, Center for
Devices and Radiological Health. Food and Drug Administration,
9200 Corporate Blvd. Rockville MD 20851

0196-655 3/2003/$30.00 + 0

258 Vol.31 No. 4 Brown and Merritt

PAN (1)

PAH (1)

PAH (2)

PAN (1)

PAN (4)

PAN (3)

Fig I. Pan 1, shown with 3 different lid designs, is
simple with no unique features. Lid A is simple
overhanging lid, much like aluminum foil stretched
over pan. Lid 6 is overhanging lid with internal
ridge, similar in concept to common kitchen
saucepan with lip to contain steam and moisture.
lid C is shaped to drop down inside pan. Pan 2 has
flat, top flange designed to engage lid D when in-
serted in pan with outer overhanging lips, which
fit snugly around flange. Sketch also shows points
under lid that represent cross-supporting ridges
acting as location for vapor to condense, much
like classic cast-iron Dutch oven lid, which has
drip points to insure uniform basting to contents.
Pans 3 and 4 are designed to confine lid within
outer lip. Pan 4 has added feature of gutter in
which outer lip of lid sits. Gutter has slots (broken
lines) that permit any condensate liquid to drip
back into pan. Lid F is insert lid with extra molding
that interdigitates with gutter and inner band
to further insure that vapor condensate returns
to pan.

Two approaches for examining the safety of decon-
taminating instruments in NaOH were taken. The
first was to have a containment device in which we
placed an open beaker with NaOH. The first
approach required a pan deep enough to hold a
beaker. The second was to fill the containment pan,
itself, with NaOH.

For the first series we used pan 2 with lid D
(Scienceware PP Instrument tray, Bel-Art Products,
Peauannock- NJ). The pan dimensions were 16 x 28

cm with a depth of 11 cm. The pan had a 1.3 cm-
wide flat rim, and the lid had a matching rim and
0.3-cm lip, which was inserted 1.2 cm below the top
of the pan. We placed an open 30-mL beaker con-
taining 10 mL of 1 N NaOH in this containment sys-
tem. Any NaOH vaporized during autoclaving would
condense on the lid, be of high pH, would cool, and
drop into the bottom of the pan. Thus, the presence
of condensate of high pH would indicate the poten-
tial for NaOH to be released into the autoclave if
there were no containment lid. Before the autoclav-
ing cycles, we placed pH paper on the top of the lid.
The pH of the condensate on the bottom of the lid
and the pH of the liquid in the pan itself were also

Pan 4 and lid F (Nalgene instrument pipet sterilizing
pan, Nalge Co, Rochester, NY) was used for the sec-
ond series of experiments. According to the manu-
facturer, this system, "conforms to National
Institutes of Health and federal register guidelines
for biohazard and recombinant DNA research where
disinfecting and subsequent autoclaving of pipets is
required before cleaning or disposal," and meets the
Occupational Safety and Health Administration
standard 29CFR part 1910.1030 for use as protec-
tion against bloodborne pathogens. This pan was 12
x 43 cm x 5.5-cm deep and the lid was fully con-
tained or inset 0.5 cm within the outer wall of the
gutter. This pan was filled to a depth of about 2 cm
with 1 L of 1 N NaOH. Several pieces of pH paper
were placed on top of the lid before autoclaving.

For these studies we used a bench-top, gravity-feed,
steam sterilizer (Harvey SterileMax, Barnstead
Thermolyne, Dubuque, IA) that has a circular inter-
nal chamber about 30 cm in diameter and 47 cm
deep. Although the WHO method calls for autoclav-
ing at 121°C for 30 minutes, it was decided to use a
worse case condition of 135°C for 1 hour, using the
"liquids, slow exhaust" cycle. This higher tempera-
ture is recommended in some of the other WHO pro-
tocols. Before and after each run, pH paper strips
were placed in several locations within the autoclave
chamber and the pH of the condensate taken after
pressure had returned to ambient and the tempera-
ture was low enough to open the door safely.

The water used for the generation of steam for this
autoclave is from a self-contained water reservoir
with a working volume of 6 L. To see if the fluid was
getting contaminated by NaOH, the autoclave was
run for 5 cycles, without water changing, with pan
4 and lid F filled with 1 L of NaOH. The pH of the

Brown and Merritt June 2003 259

water was measured before and after each run with
pH paper and a pH meter (Cole Palmer, Vernon Hills,
I11). Because the pH of the 1 N NaOH is 14 and the
distilled water used is slightly acidic, any escape of
the NaOH into the autoclave would result in an
increase in pH in the reservoir.


The condensate on the internal (underside) surfaces
of both types of lids had a pH of 14, indicating that
caustic fumes were created during autoclaving.
There was condensate with a pH of 14 on the bot-
tom of pan 2 with the open beaker indicating that
the beaker contents were released inside the pan.
There was no pH change in the condensate on the
top (outer) surface of either type of lid.

The pH of the distilled water in the autoclave reser-
voir was 5.5 before the first cycle. No change in pH
occurred in the reservoir water after each of the 5
cycles with pan 4 and lid F filled with 1 L of NaOH.
No pH change was detected at any site inside the
autoclave in the 5 sterilization cycles as indicated by
pH paper placed into the autoclave before the run
and by pH paper placed at the end of the run. Thus,
pan and beaker contents were contained by these 2
lid and pan combinations.

None of the pans and lids showed any signs of dam-
age as a result of the NaOH. Stainless steel pans and
lids have been tested, but showed signs of corrosive
attack after only limited exposure. In a subsequent
communication, the effects of the WHO decontam-
ination protocols on the instruments, themselves,
will be discussed.


The first series of tests with the type pan 2, 2-D lid
D containment demonstrated that autoclaving a
beaker containing a small amount of NaOH resulted
in condensation of caustic vapors inside the con-
tainment vessel. The pH on condensation on the
bottom of the pan, and on the underside of the lid
was 14. However, there was no pH change in the
condensate on the top (outside) of the lid or on the
internal surfaces of the autoclave. This study indi-
cates that if the containment vessel had not been
used, caustic vapors would have come in contact
with portions of the autoclave.

In the second series, pan 4 was filled with a large
volume of NaOH. Although it was only to a depth of
2 cm, the fluid level came close to the lid as a result
of the slope of the autoclave chamber. This present-
ed a large volume of NaOH compared with the 6-L
volume of the autoclave water reservoir. It also pre-
sented a large surface area of the liquid (12 x 43 cm)
compared with the dimensions of the autoclave
chamber (30 x 47 cm). Even after 5 cycles of 1 hour
at 135°C, there was no measurable change in pH of
the condensate on the top of the F lid and in the
chamber, or in the water reservoir.

These studies have demonstrated that even at the
extreme conditions of 1 hour at 135°C, compared
with the WHO recommendations of 30 minutes at
121°C, it is possible, with appropriate containment
pans and lids, to prevent escape of NaOH vapors
that might cause damage to the autoclave. These
studies have not included measurement of actual
temperatures of the liquids, which is an inherent
problem with gravity-feed, bench-top systems. It
should be pointed out that these WHO recommen-
dations are only for instrument decontamination.
After this process, routine cleaning and sterilization
with validated methods is required.

Both the pans and the autoclave used in these stud-
ies were small compared with those used in clinical
or commercial settings. By comparison, a standard
clinical autoclave may have a 51- x 76-cm opening
and be 127 cm deep (2 x 3 x 5 ft), which is a volume
15 times that of the table-top system. As such, larg-
er loads could be used in such units. More impor-
tantly, clinical autoclaves often have a preset pre-
vacuum cycle program that contains/several pulses
between high-pressure steam and vacuum. These
can not be used with liquids such as NaOH, because
the hot liquids will boil during the vacuum phase.
The use of a gravity-feed cycle, in which the pres-
sure and temperature are slowly increased, held for
a preset time, and then slowly decreased ("liquids,
slow cool") is essential for preventing boiling.

These results do not imply that these are the only
pan-and-lid combinations that would work, or that
they will work in all situations. We would anticipate
that lid A would drip outside of the pan, and lid B
would drip back into the pan. It is incumbent on the
decontamination facility to validate the method
used. Autoclaves present various hazards that are
magnified when caustic substances are used. All
standard precautions must be followed: use the
slow exhaust (liquid cycle); allow the chamber and
contents to return to ambient temperature and
pressure before opening the door; insure the liquid

Vol.31 No. 4 Brown and Merritt

is cool before handling; and take care in removing
the instruments. Disposal of the NaOH should be
done according to institutional guidelines.


1. Brown P, Gibbs CJ Jr, Rodgers-Johnson P,Asher DM, Sulima MP,
Goldfarb LG, et al. Human spongiform encephalopathy: the NIH
series of 300 cases of experimentally transmitted disease. Ann
Neurol 1994,35:513-9.

2. World Health Organization infection control guidelines for
transmissible spongiform encephalopathies. World Health
Organization/CDS/CSR/APH/CDs/CSR/APH/2000.3. Available
Accessed November 25,2002.

3. Bovine spongiform encephalopathy and Creutzfeldt-Jakob dis-
ease. [Centers for disease control and prevention Web site].
September 2001. Available at
Accessed November 25,2002.

4. Tavlor DM. Fraser H. McConnell 1. Brown DA. Brown KL. Lamza

KA, et al. Decontamination studies with the agents of bovine
spongiform encephalopathy and scrapie. Arch Virol 1994:139:


5. Burger D, Gorham JR. Observation on the remarkable stability of
transmissible mink encephalopathy virus. Res Vet Sci 1977.22:


6. Brown P, Liberski PP.WolffA, Gajdusek DC. Resistance of scrapie
infectivity to steam autoclaving after formaldehyde fixation and
limited survival after ashing at 360 degrees C: practical and the-
oretical implications. J Infect Dis 1990; 161:467-72.

7. Bernoulli C, Siegfried J, Baumgartner G, Regli F, Rabinowicz T,
Gajdusek al. Danger of accidental person-to-person trans-
mission of Creutzfeldt-Jakob disease by surgery. Lancet 1977; I:


8. Gibbs Cj Jr, Asher DM. Kobrine A, Amyx HL, Ga|dusek DC.
Transmission of Creutzfeldt-Jakob disease to a chimpanzee by
electrodes contaminated during neurosurgery. J Neurol
Neurosurg Psychiatry 1994;57:757-8.

9. Brown P, Preece M, Brandel J-P. latcogenic Creutzfeldt-Jacob dis-
ease at the millennium. Neurology 2000:55:1075-81.tss


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