ATEX REGULATIONS, INTERFACES BETWEEN ATEX 137 AND ATEX 95
The Working Conditions Act (in Belgium: ARAB) requires employers to carry out a risk inventory and evaluation (RI&E) covering the risk of explosion. Under the Working Conditions Act, an employer must take the necessary measures to prevent explosions or limit the consequences.
As of 1 July 2006, all workplaces must meet the minimum requirements of directive 1992/92/EC (ATEX 137).
The ATEX 137 directive provides minimum rules for improving health protection and employee safety in an environment with a risk of explosions. This means an explosion safety document must be drawn up presenting the degree of explosive danger in zones. Zones are determined by means of the frequency and duration of the occurrence of an explosive atmosphere as presented in the table below (see the NPR 7901-1 and –2 standards).
Each zone is associated with an equipment category in which the essential requirements for equipment is described in directive 94/9/EC (ATEX 95, compulsory since July 2003). ATEX 95 is intended for devices and security systems, both electric and non-electric, to be used in places where there may be a risk of explosion. The manufacturer, its representative or the person marketing and/or installing explosion-safe equipment will apply the ATEX 95 directive.
The fact that all workplaces must meet the minimum requirements of the ATEX 137 directive does not imply that all equipment in use meets ATEX 95. However, each workplace must be evaluated in terms of explosion risks, taking all equipment into account. Equipment that is not ATEX 95-certified is subject to a more extensive evaluation that may result in adaptations to existing equipment (improving safety) or even investment in new equipment. The extent of measure to be taken depends on the explosion risk posed by a zone.
In terms of investing in new machines, one of the biggest questions is who is responsible, when and especially for what. The answer to this question indicates the overlap between ATEX 137 and ATEX 95: where do the user and producer meet?
The user remains responsible for determining the risk of explosion and the degree of risk, expressed in the zone, and also specifies the temperature class, gas group (for gases) and degree of conductivity (for matter). Using this information, a supplier can use the ATEX 95 directive to determine the right machine and the corresponding equipment category. If a zone is assigned to a particular space, it is important in financial terms not to engage in excessive zoning. This results in additional cost and measures.
STIRRING AND MIXING IN AN ENVIRONMENT WITH A RISK OF EXPLOSION
According to the ATEX 95 directive, the possible presence of sources of ignition must be investigated, combined with the probability of incidence. A risk analysis of sources of ignition is carried out for the stirring device, in which the category determines the sources of ignition to be evaluated. A stirring device can often be used in several zones, e.g., the zone in the tank and the zone outside it, meaning that different categories must be evaluated.
The NEN-EN1127-1 standard indicates 13 sources of ignition, of which those below are most applicable to stirring devices.
- Electrical appliances
An electrical component as a source of ignition is to be eliminated if the correct electrical components are used in accordance with the ATEX 95 directive.
- Hot surfaces
This source of ignition can occur as a result of friction between stationary and moving parts (bearings and seals). The maximum surface temperature occurring must be determined for the applicable category and must be lower than the specified temperature class. Calculations of lifespan are made so that components can be replaced preventively.
- Static electricity
The degree to which this source of ignition is present is difficult to determine and the risk is often underestimated. External factors may have an effect (people carrying a static charge, powder discharge, etc.), so that a choice is made to remove the risk of explosion by means of smart design, sufficient earthing, applying antistatic materials, inertising and wearing antistatic clothing and shoes.
Static electricity occurs most often with dry matter and non-conductive liquids.
- Mechanically generated sparks
The source of ignition is created by two parts touching and forming a spark, with the risk of it immediately developing into an explosion. Removing this source of ignition is therefore the best solution by selecting the right materials, applying low relative speeds and ensuring a high degree of certainty that two parts cannot unintentionally touch.
Mechanically generated sparks together with static discharge are the cause of explosions in stirring devices in 80% of cases.
If the risk of explosion cannot be limited through solutions as part of the design (protection by constructional safety), the presence of oxygen may be eliminated (protection by liquid immersion). The required safety detectors may also be provided to further limit risks (protection by control of ignition sources).
For example, in the case of a top entry (high shear dispersion processes) in which the throughput arrives in the head space of the tank with an environment presenting a risk of explosion, a double mechanical seal with an obstructive fluid equipped with safety detectors may be chosen, with the level and temperature of the obstructive fluid being monitored.
TYPHOON AND ATEX
Typhoon Roertechniek B.V., a supplier of mixing and stirring systems for various processes in different sectors, has been actively designing and producing stirring devices since the introduction of the new ATEX 95 directive. A large number of ATEX-certified stirring devices have been delivered internationally, in addition to standard stirring devices.
DISSOLVING 105 KG OF DRY MATTER IN 35 L OF WATER
ATEX Equipment category 3D, zone 22
Complete system consisting of skid with platform for unloading pallets, hopper with doser (load cells), tank, stirring device with dispersion element and controls entirely developed and produced by Typhoon Roertechniek B.V.
MOISTENING 20 KG OF POWDER IN 80 KG OF SOLVENT
ATEX Equipment category 1G, zone 0 in the tank
Equipment category 2G, zone 1 outside the tank
System consisting of electric lift, switch panel, control box and stirring devices.
Engineering firms and end users often opt for Typhoon Roertechniek’s knowledge in mixing and stirring technology combined with ATEX.
TYPHOON ROERTECHNIEK BV, JULY 2006