Grain and feed processed within hammer mills is common fuel for dust explosions due to the nature of its handling and storage. Any time that feed such as grain, meals and flours is handled or moved, the fine organic dusts are at risk of burning and exploding.

1. Digital Re-print -
January | February 2013
Controlling the explosion risks
within hammer mills
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2. FEATURE
Controlling the explosion risks
within hammer mills
by Kevin Spiess, EMEA sales manager for
explosion protection, BS&B Safety Systems,
United Kingdom
G
rain and feed processed within pared to a detonation, which exceeds the or walls can be thrown into the air by a dust
hammer mills is common fuel for speed of sound in air. Most grain dusts are explosion, thus providing fuel for secondary
dust explosions due to the nature combustible and can cause an explosion, but explosions. Often, these secondary explo-
of its handling and storage. Any time that some types are much more dangerous than sions cause more damage than the first. In
feed such as grain, meals and flours is others, especially dust associated with corn this way, a dust explosion can jump from
handled or moved, the fine organic dusts or sugar. room to room or from silo to silo. This
are at risk of burning and exploding. The effects of accidental fires or explo- is a common phenomenon in grain dust
sions can be devastating in terms of lives explosions. For example, one of the most
lost, injuries, damage to property and the dangerous areas for grain dust explosions is
Explosion causes environment, and to business continuity. in the bucket elevator or conveying system
A fire or explosion results from ignition linked to a silo. The grain is always in motion,
of combustible material (dust, gas or vapour) Serious secondary effects so dust is constantly generated.
when mixed with oxygen in the air. When Grain dust explosions can have a cascade
this takes place inside a grain silo, process or effect. Grain dust that has settled on floors Protection measures
storage enclosure, the rapid rise in pressure An explosion risk assessment will typi-
could cause a violent explosion in millisec- cally recommend that a series of protection
onds, placing personnel and property at risk. measures be implemented. These range
Just a few burning embers entering a from investment in protection equipment
dust collector are enough to trigger a dust to improvements in housekeeping to elimi-
explosion. Likewise, combustible material nate the build-up of deposits of combusti-
conveyed into a storage silo could become ble dust which may accumulate on beams
the nucleus of a fire. Sparks or smouldering in the factory. These may be disturbed by
particles from hammer mill operations may a primary explosion in the process equip-
spread from the mill to other more vulner- ment and result in a more severe secondary
able equipment. explosion.
Most materials handling, processing and Codes and standards are now very clear
storage equipment is not designed to resist SparkEx Spark Detection and in requiring isolation of vented equipment to
the pressure of an expanding flame ball Extinguishing system prevent secondary explosions, which typi-
which proceeds below the speed of sound cally have much greater potential for damage
in air – known as a deflagration – as com- and destruction.
10 | January - february 2013 Grain &feed millinG technoloGy

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4. FEATURE
Bespoke systems processes. If unprotected, the ductwork ment and protective systems intended for
My organisation, BS&B Safety Systems, and piping, as well as all the connected use in potentially explosive atmospheres on
has launched a bespoke combustible dust vessels and equipment are at risk. This the European market.
fire and explosion prevention system for system is used in combination with explo- By investing in explosion protection,
hammer mills based on established systems sion protection equipment on each vessel, organisations can safeguard themselves eco-
developed for other
industries. The SparkEx
Spark Detection and
Extinguishing System
is designed to detect
hot particles, sparks and
glowing embers that
might become the igni-
tion source for a fire
or explosion if allowed
to travel on through
pneumatic ducting and
conveyors towards
other material handling
equipment. bin, or dust collector and could include nomically, follow appropriate health and
By preventing sparks, embers and hot chemical suppression, explosion venting or safety standards and protect workers from
particles from reaching dust rich down- indoor venting. potential risks.
stream process equipment such as dust
collectors, bins and silos, both fire and explo- Regulations, codes and standards
sion risks can be managed. Because of potential health problems,
Using infrared detectors, the system laws exist to ensure employers in the EU More InforMatIon:
detects the radiated light emitted from protect their workers from being harmed BS&B Safety Systems
sparks, glowing embers and hot particles by dangerous substances in the work- Tel: +44 161 955 4202
travelling past the detection point and acti- place. In the UK, under the Dangerous Email: sales@bsb-systems.co.uk
vates control circuits. The greatest sensitivity Substances and Explosive Atmospheres Website: www.bsbipd.com
occurs when these sensors are employed Regulations 2002 (DSEAR), all work-
in a dark area such as closed ductwork, places where substances that could
although optional daylight detectors are also give rise to fire
available for use on open conveyor belts and or explosion
for applications where light is likely to be are handled or
visible. Upon detection this system provides stored must be
several options to manage the ignition risk: fully assessed
• An electrical signal generated by and protected.
the sensor activates control circuits Employers
typically used to operate an automatic must carry out
water-extinguishing curtain. Sparks risk assessments,
can be extinguished without stopping and take steps
production. to ensure they
• An automated shut down of the prevent or
process can prevent the feed of adequately con-
combustible material. trol exposure.
• Alarm and control systems can be It is important
activated upon the detection of hot to include in
particles for other control devices such the assessment
as diverter valves. foreseeable inci-
The system detectors and control unit dents and main-
are ATEX certified for use in a dusty work- tenance work
ing environment. This means there are no and plan for
expensive costs for additional wiring to run measures to be
from detectors to remote mounted control taken in these
units and plant personnel have direct access circumstances.
to the status of the equipment. In the event ATEX is the
of an alarm condition, the operator can see name com-
immediately which process is at risk. A web monly given to
based monitoring system, which allows plant Directive 94/9/
managers to receive system alarms and faults EC which pro-
to their smart phones, as well as monitor- vides the techni-
ing the systems live on the internet, is also cal requirements
available. to be applied
In addition to this preventative sys- and the relevant
tem, systems for protection are available, conformity
should an explosion occur. A chemical assessment pro-
isolation system isolates an explosion and cedures before
prevents it from affecting interconnected placing equip-
Grain &feed millinG technoloGy January - february 2013 | 11

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explosion risks
within hammer
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