Candidate Support Pack - Scottish Qualifications Authority

Sodium hypochlorite is normally sold on the basis of available chlorine by weight, the
normal commercial strength being 14–15%. It is a relatively cheap chemical and has
the benefit that at very low concentrations (approximately 120–150 parts per million) it is
an extremely effective disinfectant.
As noted earlier, its optimum temperature for use is about 60 ºC; below this its action is
slower, and above this the action can be very rapid and can cause chemical damage to
fabrics. Bleaching with sodium hypochlorite is usually carried out in the first rinse with a
dose of approximately 6–8 ml per kg dry weight of work.
Due to the risk of chemical damage to fabrics from concentrated sodium hypochlorite, it
is usual practice to dilute it with three or four parts water before adding to the wash. On
automatic feed systems, hypochlorite bleach should always be added below the water
line and be flushed in by water.
Sodium hypochlorite bleach should not be used when washing some flame-retardant
treated fabrics as it can destroy this treatment; it will also neutralise the benefits of
enzymes and perborate/peroxide bleaches if used in the same bath.
If you start getting large brown stains appearing on hospital work after being washed in
a process that includes sodium hypochlorite, these are likely to be the result of a
chemical reaction between the hospital disinfectant chlorhexadine used in proprietary
products like Hibiscrub, Hibicleanse, Savlon, and bleach. The resulting stain cannot be
removed. The answer is prevention rather than cure so only sodium perborate,
peracetic acid or hydrogen peroxide bleach should be used on hospital work where this
type of staining might be present.
Hydrogen peroxide (H 2O 2) and peracetic acid (C 2H 4O 3)
Peracetic acid is a mixture of acetic acid and hydrogen peroxide — as the acetic acid
enhances the performance of the hydrogen peroxide. However, both products have similar
characteristics and are treated the same in this section.
Hydrogen peroxide is usually sold at a strength of 35% to the commercial laundry
market. It is inactive below 60 ºC and does not become fully active until temperatures
above 80 ºC are reached. Unlike sodium hypochlorite, hydrogen peroxide has no
bacterial effect — but peracetic acid does.
Both peracetic acid and hydrogen peroxide are considerably more expensive than
sodium hypochlorite and although only 2–3ml of bleach per kg of dry weight work is
used, it is still more expensive to use. The benefits of hydrogen peroxide are that lower
volumes need to be stored and it can be used on pastel or coloured work without
stripping the colour. Accidental chemical damage to textiles from using hydrogen
peroxide is far less likely than with sodium hypochlorite.
From a health and safety view point, all bleaches are corrosive and extreme care should
be taken when handling them.
If a product containing chlorine is accidentally mixed with peracetic acid or
peroxide, this will liberate poisonous chlorine gas and can produce an explosive
combination.
GC8N 22 — Laundry Operations Level 2 5.59