Safety is one of the most important factors for achieving a successful milling process. By its very nature milling is dangerous, as the impeller rotates inside the housing at speeds often in excess of 1,000 RPM.

In Europe, the adoption of various standards such as CE and ATEX, have helped to drastically improve safety standards, challenging both the equipment supplier and the end-user to creater a safer machine and a safer working environment. Part of achieving a safer process is the containment of hazardous material during milling. Given the aggressive nature of milling, adopting CE and ATEX standards are a great starting place for making the size reduction process safer, with CE intended to protect the operator and ATEX to protect the process environment.

CE - A Safer Operation

Throughout Europe the standard applied to enforce safety is termed as CE. The identifying letters “CE” are an abbreviation of the French phrase “Conformité Européene” which literally means “European Conformity”. These regulations are enforceable by law and many countries outside of the European Community have adopted this standard as the benchmark for safety.

‘Hanningfield supply a full range of CE-certified equipment’

The design of equipment used in the processing faces a number of challenges. Alongside achieving safety, machines intended for the process environment will also have to meet GMP requirements. Using standard safety components such as switches and interlocks can often cause problems in this regard, as the materials must be designed for use in a clean environment. Careful design is essential to ensure the best possible solution for safe and clean operation. Any manufacturer ignoring the safety obligations imposed by CE can have the operation stopped until made safe. For the manufacturer this can be disastrous causing very expensive loss of production until resolved. It is therefore essential to ensure adequate safety measures are in place when a new machine is specified.

CE is particularly relevant to milling, where it is vital to prevent the operator from accessing the screen and impeller during operation (whether accidentally or intentionally). In reality, CE should also ensure practical operation is not hindered by the integration of safety elements.

‘CE ensures features such as safety-grids and safety-switches are used to help prevent hazards when operating the mill’

Typically the main hazard when milling is the rotating impeller which forces material through a stationary perforated milling screen. The operator must be protected from moving parts and this is achieved using interlock switches appropriate to the application. For example standard off-the-shelf machines will be supplied with interlocks already in place, whereas machines which require integration into an existing process will require a custom made design to provide adequate protection. All mills can be a hazard to the machine operator. Therefore it is imperative to understand and overcome such hazards in the most effective yet operator-friendly way.

ATEX - A Safer Environment

The introduction of ATEX has been one of the most significant changes to European processing in recent years. ATEX is the harmonised European standard created to ensure all equipment located in the process environment complies with the safety specifications of the directive. There are currently two European directives in existence; 94/9/EC, which is principally for manufacturers and 99/92/EC, for operators of the equipment. The basic function of ATEX is to prevent explosion in an atmosphere where such an occurrence is possible.

‘ATEX is a European standard for explosion proof equipment’

The risk of explosion in pharmaceutical, food and chemical manufacturing facilities is a very real prospect. A seized bearing or mechanical failure can generate excessive heat and is deemed as likely to cause an explosion as an electrical fault. It is therefore important to consider such factors in the design and use of processing equipment, such as mills. This is an important point, as ATEX also takes into consideration mechanical design, where existing standards are concerned with only the electrical aspect of machinery design.

To meet ATEX standards, a number of safety measures are necessary to eliminate potential risks. This is initially conducted by the customer on the product to be milled via a risk analysis (Ignition Hazard Assessment), which will also evaluate the environment in which the size reduction process will occur. This outcome of this assessment determines the type of hazardous zoning required inside and outside of the mill. Under ATEX regulations, hazardous areas for explosive dust atmospheres are classified into three zones:

1. Zone 20 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is present continuously, for long periods or frequently.

2. Zone 21 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is likely to occasionally occur in normal operation.

3. Zone 22 is an area in which an explosive atmosphere, in the form of a cloud of combustible dust, is not likely to occur in normal operation but, if it does occur, will persist for a short period.

Once the machine supplier understands the Zoning requirements, the mill can be designed to meet the appropriate ATEX Directive measures. For a milling application, this may include an earth-bonding strap, temperature probe (for monitoring screen heat) or nitrogen-purging, depending on the potential hazard, and therefore the relevant zone.

It is essential to match the equipment with the corresponding process environment. If the equipment is situated in an ATEX zoned area then the external features of the mill must comply with the ATEX provisions according to the zone. Necessary precautions should be taken relating to the effect on the surrounding area and also effects resulting from the surrounding area.

Importantly for milling applications, it is possible to create an ATEX environment, in a non-ATEX room by housing the mill inside an isolator. Providing everything inside the isolator is ATEX-compliant, the isolator itself becomes regarded as an ATEX zone, negating the need to upgrade the entire process room to comply with ATEX. This approach offers the safety benefits of ATEX milling, but at a reduced and manageable cost.

Achieving a Safer Process

By exploring best practices such as CE and ATEX, global manufacturers can benefit from proven, existing safety standards. In considering ways to make processes safer, manufacturers can better comply with their own local standards, such as those outlined by the FDA in North America.

Hanningfield have more than 25 years in powder processing, handling and containment. The company manufactures a cone mill, which is designed and manufactured at the company’s UK manufacturing facility. The company can offer consultation for helping with CE or ATEX requirements, and can offer various custom designs to suit specific application requirements, such as mobile frames, hoist/lift integration, removable mill-heads, cryo-milling and CIP.