(NaCl). It is produced by passing chlorine gas
through a dilute sodium hydroxide solution or by
electrolysis of salt water. Sodium hypochlorite is
reactive and may chlorinate organic compounds. 8
This solution contains HOCl in equilibrium with
the hypochlorite ion as shown by the equations
NaOCl → Na+ + OCl-
OCl- + H+ ; HOCl (hypochlorous acid)
Sodium Dichloroisocyanurate: NaDCC is formed
through the pyrolysis of urea which forms cyanuric
acid. The cyanuric acid is reacted with chlorine
and sodium hydroxide to form NaDCC. 9 In water,
the NaDCC forms HOCl in equilibrium with a
complex mixture of various chlorinated cyanurate
chemical species. 10
NaCl2(NCO) 3 + H2O ; 2HOCl + NaH2(NCO) 3
The NaDCC used in this experiment was supplied by Brulin & Company, Inc. (EPA Registration
Number 71847-2-106). 11 On the label, the use
instructions indicate adding one tablet per gallon for 937 ppm active chlorine.
To make a 1: 10 bleach solution ( 5,000-ppm active chlorine), 1¾ cup
bleach is added to one gallon of water with mixing as described by the
bleach EPA label. For the 1,000-ppm NaDCC solution, one tablet is added
to one gallon of water and allowed to dissolve through the effervescence,
a process that takes less than two minutes. Each product is to be used per
EPA registration label guidelines on hard, nonporous, inanimate surfaces
that have been pre-cleaned. The products are applied to the pre-cleaned
surface. The surface must remain wet for the prescribed contact time of
ten minutes. If the surface dries before ten minutes, the reapplication of
more solution is required. After ten minutes, the product may be allowed
to dry on the surface or be removed.
While bleach is used to disinfect hard, nonporous, inanimate surfac-
es, as found on the Clorox® Bleach label, 12 it also includes the following
instructions, not found in the NaDCC product label:
• “Do not use this product on steel, aluminum, silver, or chipped enamel.
• If used on metal, a solution of this product should be allowed to stand
for no more than five minutes, and then rinsed off thoroughly with
clean water; otherwise, it may slightly discolor and eventually corrode
It is interesting to note that the second instruction for limiting expo-
sure to five minutes is less than the prescribed contact time.
This study shows the corrosive effects of bleach solutions on 304L and
316 coupons at use levels typically employed for equipment disinfection
in the pharmaceutical, bioprocessing, and medical device industries as
part of their standard operating procedures. The NaDCC solutions did
not show corrosive effects to the stainless steel coupons as shown in
Figures 4 and 5.
Users of diluted bleach solutions on stainless steel must replace carts,
Figure 2. The photograph shows the clean face of a 316 coupon exposed to 1,000-
ppm NaDCC solution for three weeks.
Figure 3. The photograph shows rust remaining at the bottom of the beaker that contained the more corrosion resistant 316 coupons exposed to the more commonly used 1: 10 bleach solution. Even though the experiment finished at
eight weeks, the 316 coupons were soaked for an additional month until metal deposits were showing in the beaker.