TURNED
TO DUST
Paper, metal,
plastics can
generate
combustible
dust in
recycling
facilities
TURNED
Three workers were killed and a con-
tract employee injured.
The hazard of combustible dust
explosion may be most associated
with the wood and food industries,
which have seen high-profi le incidents
in recent years, but the hazard presents
a major risk in the recycling industry
as well. Materials handled in recycling
facilities are highly combustible and
people are often unaware of the haz-
ards they present during processing.
A dust explosion occurs when an
explosive dust cloud (consisting of an
adequately mixed fuel and oxidant)
is formed and ignited by a suffi -
ciently energetic ignition source in a
confi ned or partially confi ned envi-
ronment, says Paul Amyotte, professor
of chemical engineering at Dalhousie
University in Halifax.
In recycling, dusts or powders gen-
erated during the processing of paper,
metal, plastics and rubber (rubber
crumb) constitute the fuel. Ignition
sources include welding, static elec-
tricity and equipment power systems.
The confi ned space may be a building
section or piece of equipment.
Processes commonly used in
recycling — shredding, cutting and
shaving — can create large amounts
of combustible dusts. With some
materials, handling and conveying
can generate fi ne particles that may be
hazardous. In the case of paper and
cardboard, for example, the hazard is
greatest at the beginning of the pro-
cessing, says Graeme Norval, associate
chair and undergraduate co-ordinator
in the department of chemical engi-
neering and applied chemistry at the
University of Toronto.
"When they bring in the dry paper
and they're cutting up the bales, they
have to shred that down into fi ne par-
ticle size. That's where you can get dust
coming off and airborne matter," he
says. "Once they put it all into water,
and they do the dispersion to get the
inks off, it's all wet, there's no dust.
So, dust is not a problem in the whole
plant, just in parts of the plant when
the material is dry."
In metal recycling, small particles
are created through a range of pro-
cesses, which, in addition to milling,
include scrap chopping, cutting, han-
dling, sawing and fi ling. Some of these
processes, especially baling, compact-
ing and shredding, produce signifi cant
amounts of dusts.
Among the most hazardous metal
I
n the 15 years before an explosion
occurred that would destroy the
A.L. Solutions metal recycling plant,
there had been two fatal fi res and
explosions at the facility. The West
Virginia plant, which processed scrap
titanium and zirconium metal, con-
tinued to ignore safety standards
and use inappropriate control mea-
sures. Then, in December 2010, a
spark of heat in a defective blender
ignited milled zirconium particulates,
producing a fl ash fi re that lifted some
of the powder into the air and creat-
ing a burning metal dust cloud. The
cloud, in turn, set fi re to other dust in
the facility, and a secondary explosion
blew though the production plant.
By Linda Johnson
26 Canadian Occupational Safety www.cos-mag.com
