Dust and fumes are the enemy of process-based operations – airborne contaminants present both a health risk to employees, as well as significantly impacting on productivity, reports Susan Fearn Ringsell
All businesses have a legal obligation to ensure safe working environments for the people they employ.
For process industries, this means maintaining a dust and fume-free workplace through the removal of solid particles [particulates], liquid droplets [usually aerosols or mists] and vapours or gases by way of an appropriate dust and fume extraction system.
“Typically,” explains John Horsey, technical manager at BOFA International, “emissions are produced through activities such as laser and ink jet coding onto food and pharmaceuticals packaging, soldering, welding, laser cutting and engraving, spraying, and hand and mechanised grinding.”
Dust is a concern for occupational hygiene and personal dust monitors are used in the pharmaceutical industry to monitor operator exposure to potent chemicals
Keith Plumb, process and equipment consultant at BPE
Exposure levels to potentially harmful airborne emissions are tightly mandated through the Control of Substances Hazardous to Health (COSHH) regulations under the direction of the Health and Safety Executive (HSE), and are expressed as workplace exposure limits (WELs).
Horsey adds: “Where control measures are installed, these must be thoroughly inspected and tested at least once every 14 months (in practice every 12 months) and a suitable record must be kept of the examinations and tests for at least five years.”
Keith Plumb, process and equipment consultant at BPE, says: “Dust is a concern for occupational hygiene and personal dust monitors are used in the pharmaceutical industry to monitor operator exposure to potent chemicals.”
Recently, European good practice has been incorporated into IEC standards along with good practice from other countries. This has led to the IEC 60079 series of standards, covering such subjects as hazardous area classification and the design, testing and selection of electrical equipment.
Risky business
From a process perspective, fugitive dust is caused by ineffective local exhaust ventilation, and the key decision for plant and health and safety managers is to evaluate the most effective means of extracting airborne emissions.
Horsey explains: “Typically, these might include captor hoods, which depend upon a capture velocity in front of a nozzle; receptor hoods, which use the movement of particles or droplets towards the device to capture them; partial enclosures, which extract contaminants typically for hand grinding and finishing; and full enclosures matched to the needs of automated production in say the laser coding or PCB manufacture.”
There are also challenges that go beyond capture. For example, extraction systems linked to high temperature industrial processes – such as lasers – need to take account of potential fire risks.
Sadly, dust explosions have been part of food and beverage manufacturing for some time with the first recorded dust explosion taking place in a flour warehouse in Turin in 1795. Two boys were injured but no one was killed in the incident.
However, as the scale of industrial processes has grown, so has the size of the dust explosions.
Says Plumb: “In 2008 there was an explosion at the Imperial Sugar Company in the US state of Georgia that killed 14 people and injured 36. A series of explosions took place, the first of which was initiated in an enclosed steel belt conveyor located under the sugar silos.
“The recently installed covers allowed explosive concentrations of sugar dust to accumulate. A secondary explosion arose because of sugar dust accumulations and this explosion propagated through large parts of the site.”
Critical contamination
Horsey says: “Not all airborne contaminants present significant risk to human health. It is those contaminants measuring two to three microns that are of particular concern for respiratory function because these can penetrate into the alveolar lung region more than any others.
“Moreover, while particles of less than 0.5 microns will mostly be exhaled, if soluble they can diffuse into the bloodstream. The smallest particles (nano particles) can pass into the pleural cavity and lodge there.”
While the particle itself may not be a problem, it can carry complex chemicals and some of these can trigger reactions in the body.
Poor dust and fume management not only exposes workers to risk of harm, but could also result in criminal and civil action with financial penalties and reputational damage.
It also has a negative impact on productivity through downtime caused by equipment contamination.
Hundreds of kilograms of accumulated dust has been recorded in industrial ceiling spaces and has been known to fuel devastating dust explosions
Mark Shannon, UK and Ireland sales manager, BS&B Safety Systems
Dust that has escaped and allowed to settle on floors or walls can be dispersed into the atmosphere by a primary dust explosion. Theoretically, when one element of the trinity of ignition, fuel and oxygen is interrupted, an explosion can be prevented; there are various measures available to interrupt a growing deflagration.
“Hundreds of kilograms of accumulated dust has been recorded in industrial ceiling spaces and has been known to fuel devastating dust explosions,” explains Mark Shannon, UK and Ireland sales manager, BS&B Safety Systems. “Quite often, none of the staff suspects the danger that hides right above their heads.”
Large amounts of accumulated dust disturbed by a primary explosion in the process equipment can result in a more severe secondary explosion as the suspended dust fuels the initial incident.
The UK Health and Safety Executive recommends that as well as a rigorous cleaning regimen, the elimination of high-level horizontal surfaces is preferable; for example, by use of sloping surfaces to minimise dust accumulation.
All aspects of the dust’s behaviour in relation to its process environment can be determined to inform the correct precautionary measures against a potential explosion.
Trending technology
Innovation in system design, filtration technology, diagnostic connectivity and sector application is increasingly important in dust and fume extraction.
BOFA, for example, has won a Queen’s Award for Enterprise: Innovation – for its Intelligent Operating (iQ) System [pictured below] – which has introduced performance enhancements, such as independent filter status monitoring, to improve extraction efficiency.
This ensures that filters are changed at just the right time, thereby reducing the risk of downtime and lowering the overall cost of ownership. The technology includes local and remote diagnostics capability – and this connectivity is set to expand into enhanced configuration and diagnostics.
Filtration technology is also advancing, through BOFA’s patented DeepPleat Duo pre-filtration, which uses reverse airflow operation to reduce the velocity of contaminant as it enters the filter chamber.
At BPE, the approach to dust explosions risk is award-winning and used by IChemE in its training.
Plumb explains: “Our new methodology came about after we identified that while there is a clear legal requirement to reduce the risk from explosive dusts and carry out a hazardous area classification, no rigorous yet simple step-by-step approach existed.”
Most people think that dust is, for the most part, the same. However, the range and qualities of dangerous dusts are expansive across the process industries
BPE decided to create a toolkit to help process engineers explore the risks and provide practical solutions to help to secure targeted reduction in the risk of dust explosions.
“The toolkit has already proven successful, having been implemented at a number of different sites, including a pharmaceutical solid dosage plant, a creams manufacturing plant, and a site that produces equipment for shot blasting metal and plastic parts,” says Plumb.
“Most people think that dust is, for the most part, the same. However, the range and qualities of dangerous dusts are expansive across the process industries and include organic materials that most of us would not even consider as an explosive risk,” says Shannon.
Nevertheless, for the purposes of manufacturing and processing, trending technology can provide a closer analysis of dust characteristics required to specify operational conditions, protection and extraction.
