Controlling explosion risks

A huge blast at a fertiliser plant in Texas on April 17th, which killed 14 people and injured 200, is a reminder of the risks of industrial explosions. The blast, which is thought to have been accidental, left much of the landscape surrounding the West Fertilizer Company unrecognisable, with what was once a corn silo crumpled in the force of the blast.

Any industry which handles, stores and processes solids and bulk materials is at risk of the fine organic dusts from these substances burning and exploding. Every year, premises are severely damaged or destroyed by dust fires that usually start in dust extraction equipment. Just a few burning embers entering a dust collector, bin or silo are enough to trigger a dust explosion which would typically lead to fire.

The effects of accidental fires or explosions can be devastating in terms of lives lost, injuries, damage to property and the environment, and to business continuity.

A fire or explosion results from ignition of combustible material (dust, gas or vapour) when mixed with oxygen in the air. When this takes place inside a silo, process or storage enclosure, the rapid rise in pressure could cause a potential violent explosion in milliseconds, placing personnel and property at risk.

Dust that has settled on floors or walls can be thrown into the air by a dust explosion, thus providing fuel for secondary explosions, which can cause more damage than the first. 

Protection measures 

Protection measures range from investment in protection equipment to improvements in housekeeping to eliminate the build-up of deposits of combustible dust which may accumulate on beams in the factory. 

Bespoke spark detection and explosion prevention systems are available which are designed to detect hot particles, sparks and glowing embers that might become the ignition source for a fire or explosion if allowed to travel on through pneumatic ducting and conveyors towards other material handling equipment.

By preventing sparks from reaching dust rich downstream process equipment such as dust collectors, bins and silos, both fire and explosion risks can be managed.

Infra-red detectors spot the radiated light emitted from sparks, glowing embers and hot particles travelling past the detection point and activate control circuits. The greatest sensitivity occurs when these sensors are employed in a dark area such as closed ductwork, although optional daylight detectors are available for use on open conveyor belts and for applications where light is likely to be visible. Upon detection, systems provide several options to manage the ignition risk:

• An electrical signal generated by the sensor activates control circuits typically used to operate an automatic water extinguishing curtain. Sparks can be extinguished without stopping production
• An automated shut down of the process can prevent the feed of combustible material 
• Alarm and control systems can be activated upon the detection of hot particles for other control devices such as diverter valves

In addition to this preventative approach, protection methods are available, should an explosion occur. Chemical isolation systems segregate an explosion and prevent it from affecting interconnected processes. If unprotected, the ductwork and piping, as well as all the connected vessels and equipment are at risk. This system can be used in combination with explosion protection equipment on each vessel, bin, or dust collector and could include chemical suppression, explosion venting or indoor venting.

Regulations, codes and standards

In the UK, under the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR), all workplaces where substances that could give rise to fire or explosion are handled or stored must be fully assessed and protected.  

Employers must carry out risk assessments, and take steps to ensure they prevent or adequately control exposure. It is important to include in the assessment foreseeable incidents and maintenance work, and plan for measures to be taken in these circumstances.

ATEX is the name commonly given to Directive 94/9/EC which provides the technical requirements to be applied and the relevant conformity assessment procedures before placing equipment and protective systems intended for use in potentially explosive atmospheres on the European market. 

By investing in explosion protection, organisations can protect themselves economically, follow appropriate health and safety standards and protect workers from potential risks. 

Kevin Spiess is EMEA sales manager for explosion protection at BS&B Safety Systems