There have been newsworthy examples of grain mill fires around Europe in recent years: 2010 Verdelot in France saw the destruction of Moulins Bourgeois mill; in 2014 a major fire broke out in Chancelot Mill in Edinburgh. Recently in 2015 a fire consumed Allied Mills at Tilbury Docks, London.

The originating causes of grain mill fires may be varied; a spark, a carelessly discarded match, electrical fault, or grinding and milling friction. However, the fuelling and propagation of a possibly fatal explosion is almost always caused by grain dust.

Why are hammer mills an explosion risk?Among the locations commonly identified for primary dust

explosions, hammer mills sit as a leading contender for explosion initiation. Hammer mills are sources of explosion ignition

because they pulverize raw materials against a surface at high impact. When surfaces contact in this way, the impact and friction causes sparks and hot spots, which are ideal ignition sources for dust accumulations or dust clouds.

According to the UK Health and Safety Executive (HSE) guidance on Prevention of Dust Explosions in Food Industry (Milling and Grinding):

“Hammer mills are often engineered to be strong enough to contain a dust explosion, but sparks or smouldering particles may spread from the mill to other more vulnerable equipment.”

However, what are the consequences when a hammer mill fails to contain such an explosion?

The very nature of the materials being processed and handled turn a hammer mill into a potential tinder box. Explosions are caused by the trinity of ignition, fuel and oxygen. When these three elements come together in an enclosed area, with rising pressure and rapid increases in temperature, a deflagration can occur. This primary explosion can cause a pressure wave carrying with it a flame that disturbs accumulated grain dust. Nearby personnel and property are now at great risk of harm.

Post ignition hazards Unfortunately, once the agitated dust is in suspension, this

is where the extremely dangerous secondary explosion risk is created. The secondary explosion has the ability to spread to other

STOR

AGE

Devastating mill explosions pose one of the most significant safety risks in the grain and feed industry. The milling, handling and storage of grain and feed - whether wheat, rice and barley, or sugar and corn - constitute explosion risks in spite of their innocuous nature.

Ima

ge

: © M

eu

nie

rd |

Dre

am

stim

e.c

om

Is suppression the solution in grain hammer mills?by Kevin Spiess, EMEA Sales Manager for Explosion Protection, BS&B Safety Systems, UK

Dust explosion #2

58 | Milling and Grain

F

parts of processing equipment risking its complete destruction. It travels through pipes, ductwork and silos until no part of the mill is safe from the mobile explosion risk - including the mill building structure.

In theory, when one element of the incendiary trinity is interrupted or controlled, an explosion can be averted. This invites different methods of protection to mitigate against fire risk ranging from better housekeeping to reduce or eliminate dust accumulation, to venting systems and explosion suppression devices.

Early detection BS&B have taken explosion suppression methods to a new level

of efficiency with the new the System V. System V is designed to detect the start of an explosion and deliver dry chemical extinguishing agents into a developing internal deflagration via a Cannon™. In this way it suppresses further flame propagation and protects interconnecting process equipment from any spreading explosion damage.

In environments where the by-product of bulk handling and processing is highly combustible dust, this system detects danger at the first suggestion of risk. It is made up two main elements. The Cannon™, which delivers the extinguishing agent, is a modular design consisting of five components:• the Cannon body• extinguishing agent canister• actuation mechanism• pressurized nitrogen tank• Cannon electrical enclosure

The second element is the Smart Controller Unit with sensors that detect the slightest temperature fluctuations and indicate a potential deflagration forming. This timely detection is the key to

avoiding a potential explosion disaster.When the Cannon deploys, it releases sodium bicarbonate to

suppress a dust explosion. Deployment is prompted by a low voltage electrical signal generated from sensors in the Smart Controller Unit, which activates actuators in the Cannon. The actuators release pressurized nitrogen gas at the sodium bicarbonate canister, which in turn, fires its contents at high speed in just a few milliseconds. A possible explosion travelling through connected equipment is safely and quickly averted. The result: no persons injured by a spreading explosion and untold damage to equipment is avoided.

Figure1: The explosion suppression system is designed to detect the start of

an explosion and deliver dry chemical extinguishing agents into a developing

internal deflagration. In this way it suppresses further flame propagation and protects interconnecting process

equipment from any spreading explosion damage.

July 2015 | 59

F

User flexibility and regulatory complianceThe System V is lightweight and modular, enabling easy

shipping, fitting and maintenance, making it user friendly at each stage of the supply chain.

BS&B are very aware of a need to make protection systems

simpler to use for the end-user. Therefore, the Cannon’s critical circuits are continuously monitored and any events are reported at a controller’s touch screen. To ensure personnel and property safety, there are equipment failsafe features. The dual lockout mechanism prevents accidental discharge of a Cannon

into the protected equipment when client operatives may be conducting internal work in the vicinity.

The end-user has full control over refit and maintenance. With appropriate training from BS&B, an appointed operative can refit the system using simple replacement parts after it has been activated. This reduces interruption on production time and any ensuing economic loss.

As employers are required to adhere to DSEAR 2002 and ATEX 95, the System V has been designed to be a flexible, cost effective and efficient means to help them meet those requirements. It is recommended that before installation, correct specification of the dust likely to cause an explosion hazard is identified. In this way the client can install the appropriate size of Cannon for optimal protection of staff, equipment and property.

Protecting your businessThe appeal of applying

explosion suppression as a protective measure, is that it pre-empts explosion danger via sensitive detection and prompt action. The accuracy of response means that lives are not unnecessarily endangered, equipment is saved from destruction and in the worst case, the entire milling business is not rendered inoperable due to an explosion-induced fire.

www.bsbipd.com

“The originating causes of grain mill fires may be varied;

a spark, a carelessly discarded match, electrical fault, or

grinding and milling friction. However, the fuelling and

propagation of a possibly fatal explosion is almost always

caused by grain dust”

STOR

AGE

60 | Milling and Grain

F