Dust and Fume Control: Clearing the Air01 February 2005

Implementing dust and fume control measures is key to providing a safe working environment, with current legislation and best practice extending the scope of control well beyond the factory. Where activity is undertaken that gives rise to hazardous dust and fumes, the definitive requirements for compliance are specified in UK health and safety regulations and a number of EU directives. Across Europe, the European Agency for Safety and Health at Work collects, analyses and publishes information - in its Third European Survey on working conditions, it was reported that as many as 22% of employees breathe in vapours, fumes, dust or dangerous substances during one quarter of their working time. Some areas of Europe are worse than others, but everywhere it seems apprentices and blue-collar workers are significantly more exposed than others.

There are many industries where the production processes obviously give off toxic or harmful fumes, in others these may be less obvious. Simply venting to atmosphere - removing the toxic hazard from the workspace - is not an option. The by-products of the process need to be treated effectively to ensure that any external as well as internal emissions are within the safe limit guidelines, and present no hazard to the health of employees or the general public.

Safe operation of industrial plant that controls the level of emission of dust and fumes is a benefit to the success of the company and its products. The consequences of not managing these emissions can and has resulted in injury, illness and even death. Employers have to comply with the Control of Substances Hazardous to Health Regulations 2002 (COSHH). These set out eight key steps to take:
- Assess the risks
- Decide what precautions are needed
- Prevent or adequately control exposure - Ensure that control measures are used and maintained
- Monitor the exposure
- Carry out appropriate health surveillance
- Prepare plans and procedures to deal with accidents, incidents and emergencies
- Ensure employees are properly informed, trained and supervised.

All industries must address the issue of dust and fume control, with health and safety legislation as the key driver for control. While fumes can be seen as more hazardous and volatile, dust is present in many industries; correct and safe handling will reduce the risk of a dust explosion. Such events take place in industries as diverse as food production (sugar, flour, custard powder), wood machining, papermaking, organic chemicals, plastics, metal powders and minerals. The consequences of not tackling the problems are potentially huge, and will impact the viability of the organisation through the insurability of its facilities and machinery.

In the words of the European Agency for Safety and Health at Work, "proper management of dangerous substances protects workers and the environment while ensuring the quality of the products". Indeed the rewards of implementing effective dust and fume control systems can bring financial as well as health benefits. An example cited by the agency is a UK printing facility which, with little cash spent, saved more than £50,000 a year and halved the levels of solvent vapour in the workplace.

In industries where lasers are used to mark or etch information onto products, there is a need to ensure control of dust and fumes. Hazardous dust is created during the marking process, as the lasers cut, etch or engrave the product, which may be plastic, ceramic, glass, wood, rubber and even cardboard. Without effective removal of the dust, the laser lenses may become dirty, the mark itself may not be made accurately, the product may be contaminated, and of course, the employees using the tools may be exposed to harmful dust. In each case, the lack of effective dust extraction can cause production delays, damage to machinery and increases in staff sickness levels - and these may be the least of the problems. An ineffective system can result in compensation claims from employees and non-compliance with COSHH regulations.

Just as varied as the industries that generate dust and fumes are the wide range of types, functions and services from the specialist industries that supply the solutions. Dependent on whether the workplace is a bench, workshop or manufacturing production line, ducted fans, portable appliances, or laminar flow booths may be deployed. Other important criteria include the type and volume of generated material, along with the hazard they present to the environment and health of the workforce.

- Portable and bench top equipment can come in a bewildering variety of shapes and sizes. Some are carried on trolleys in the form of a cabinet that can be positioned wherever the work is being undertaken.

- At the workbench almost every conceivable arrangement has been tried and used, with small booths and enclosures, surmounted by fans ducting the gases away from the working area.

- Industrial vacuum systems can be used in a wide variety of applications including removal of welding fumes, dust from grinders, metal chips from cutting tools, and other types of dust. The resulting residue is then collected in filters for subsequent disposal.

- Laminar flow booths function by drawing air through perforated walls into a plenum chamber, taking the hazardous material away from the operator completely. These are especially useful where the operation involves weighing and filling drums with dust and fume producing chemicals

- Filters are an integral part of any extraction system, and nowadays are often of modular design, including particle, gas, metal and micro filters, arranged in sequence to suit the application.

- Cyclonic wet extraction systems are often used by industries that use spraying techniques for metal powder or ceramic coatings. With dust particulate emissions very restricted, the extraction process is a multi-stage operation. The major benefit is the lack of internal moving parts, and there are no filters to change; only the external fans and pumps require routine maintenance.

Another good example of the diversity of the installations where dust and fume extraction equipment is put to very effective use is in the processing of the humble potato. Wisbech-based Greenvale Foods installed extraction equipment made by the Air Services Division of Carter Environmental Engineers (CEE), to remove starch and product-laden steam from the production area of its newly upgraded potato processing plant. A division of leading potato supplier Greenvale AP, the company has invested £1.5m to double dehydrated potato flake production capacity to 16,000 tonnes a year.

The system was designed and installed by lead contractor Environmental Engineering UK, including fanset, ductwork and noise attenuation. It provides extraction of starch-laden steam from the cooking and dehydration processes, with cleaned air and steam vented to atmosphere. Following cooking and dehydration, the product is ground to a specified particle size for use in the snack food industry.

Combining multi-stage cleaning in a single unit, the Cyclovent typically requires 25% less energy for the same efficiency than conventional single-stage venturi scrubbers. Alternatively it will achieve significantly greater collection efficiency than a conventional unit operating at the same pressure loss. The simple Cyclovent design does not require expensive specialist components or control equipment. It is effectively self-cleaning, and is particularly suitable for problematic sticky gas streams.

The range of industrial processes gives rise to a large number of potential solutions, but which one is right for your process? How can you provide a costeffective solution? The approach advised under COSHH regulations is to remove or reduce the exposure to acceptable levels. A first consideration is to change the process or activity so that the hazard is no longer generated; replace it with a safer process, or use the hazardous material in a safer form.

An example of a such change in process is a case, referred to by European Agency for Safety and Health at Work, where a manufacturer of arc welding systems replaced high-solid painting by powder coating. A powder booth and an environmental room were installed, reducing employee exposure to organic solvents, and improvements in the control of dust emissions. On top of this, it was found that powder coating produced greater resistance to corrosion and a better finish.

In metal treatment industries - such as cutting, machining, or profiling - some machinery comes with extraction equipment already fitted, but occasionally only around the working area, and within the confines of the equipment. Extracting dust in particular requires attention to be paid to ensuring the volume of air and its velocity, and interconnecting pipework and fans, adequately meet the need to collect and remove the dust from the workspace.

Consider the example of fume extractor arms used in a welding process. Under normal welding operations, the recommended airflow at the working area is 800 m3/hour. Achieving this where multiple workspaces, and consequently multiple extraction points, are concerned depends on the correct calculation of pressure drop, fan size and ducting layout. This type of initial analysis could be applied with equal effect to small workshops, garage repair bays and light industrial premises.

When choosing a system, always note that there are hidden operational costs in buying a low-cost installation that initially meets the process need; with very low-cost fume extractors there is a trade-off between performance, filter life and perhaps even safety. For large installations, similar design, planning and installation criteria apply. Selecting the right fan, filter and ducting is critical to the success of the finally installed system, and whether or not the production operations meet required safety regulations.

When it comes to maintaining the systems, there are clearly defined criteria for controlling dust and fume extraction processes (some international, and some local), all of which are governed to a degree by the COSHH regulations for LEV (local exhaust ventilation). This advocates weekly inspections for LEV equipment as part of the plant maintenance schedule, but there are also statutory requirements to be fulfilled. For instance, extraction equipment must, in general, be fully examined once every 14 months, with the results recorded. For non-ferrous foundries and processes where metal dust is produced, this interval is six months.

Equipment manufacturers have improved their products in many instances to reduce downtime, and utilised innovative techniques to automate cleaning. Some of these include periodic reversal of airflows to clean filters, and containers, bags or tanks to store the material prior to disposal.

Filters are an integral part of dust and fume extraction systems, with pre-filter filters to prevent premature blockage of the main filters, some of which may be HEPA (high-efficiency particulate arresting) filters. These types of filter were originally developed for the nuclear industry, many years ago, and at best can remove up to 99.7% of particulates from the atmosphere.

Some designs are a concertina, or pleated arrangement, the general purpose of which is to extend the life of the filters, reducing downtime for filter changing. Vacuum systems may be designed to suit most businesses and processes, whilst in some cases use of fixed rather than portable systems can lower servicing costs, and with the use of automatic valves, additional reductions can be achieved. Overall, the design and installation of any extraction system can be a key factor in determining the most cost-effective business process operation.

SOE

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