Genevac - Evaporation Pure and Simple

Introduction

There are two European directives covering personnel and equipment in potentially explosive atmospheres. These ‘New Approach’ directives are:

As of 1st July 2003, both directives are now mandatory within the European Union. This document seeks to clarify Genevac’s position regarding this legislation.

It is the responsibility of the user of the equipment to classify (Zone) their particular environment in order to determine if there are any particular requirements placed upon the equipment they are about to use. Centrifugal Evaporators are operated within either a chemistry laboratory or a fume hood, so it is these environments that must be considered.

As stated previously, the final decision regarding the zoning of this environment is the responsibility of the user. If it is decided that the environment has to be considered as zone 0, zone 1 or zone 2, then this places requirements on the equipment supplied and intended to be used within that environment. For example, should zone 2 be chosen (the least demanding) then the equipment must, as a minimum, conform to the requirements of Category 3 equipment. Note; this would be a minimum requirement and the purchaser of the equipment could only make the final decision on the category of the equipment after an appropriate risk assessment.

Discussions held with several users of our evaporators have confirmed that they consider the general laboratory and ‘fully extracted’ fume hood environments to be classified as Safe Areas. For these users therefore, there are no special requirements placed on the equipment in the context of the ATEX 137 Directive. All Genevac systems are suitable for use in Safe Areas, and therefore suitable for use in laboratories and fume hoods considered to be safe areas.

The position regarding re-circulating fume hoods is, however, less clear. The final decision for these fume hoods would depend on a number of factors, which may include the types of solvent being used, the frequency of use and the quantities of solvent involved and working practices. For example, any potential risk of an explosive atmosphere would be reduced if common working practice in a lab were to immediately clear up any solvent spillage. The user of the fume hood must take this decision. Should it be decided, for example, that the area is Zone 2, then equipment of at least Category 3 would be required. Genevac Ltd has evaluated the design of its evaporator systems and believes that they do not meet the requirements of Category 1, 2 or 3 equipment.

It should be stressed here that we firmly believe this to also be true of many other pieces of equipment within the lab environment. For example, there are usually personal computers within a laboratory. These similarly could not be considered to meet Category 1, 2 or 3 requirements.

It is necessary also to consider the risks created by the evaporator when volatile flammable solvents are placed inside the system. Examples of factors to be taken into account when attempting to quantify this risk are:

Quantity of solvent involved
Vapour concentration range over which the air/solvent mixture is potentially explosive
Auto ignition temperature and ignition energy.
Flash point.
Energy released as a consequence of an ignition.
It is the responsibility of the user of the system to evaluate this risk.

The question of whether or not the internal environment comes within the scope of the directive is unclear. The ATEX directive concerns "electrical and mechanical equipment placed within a potentially explosive environment at atmospheric pressure". Technically therefore, the internal environment of the evaporator does not come within the scope of the ATEX directive. However, Genevac has an obligation under a general duty of care to supply systems that are safe to use and therefore we have considered the internal environment within the context of the intent of the directive. Genevac Ltd believes that its products meet such an obligation, with risks being minimal. We offer the following discussion to support this:

1. With most Genevac systems the chamber pressure must be below 400 mbar before power is supplied to the infra-red heating lamps. It is well documented that the energy required to ignite gas or vapour at low absolute pressures are very high. Consequently ignitions when an evaporator is under vacuum are extremely unlikely and were one to occur, there would be very little or no oxygen present.

2. Typical evaporation runs require the use of a vacuum of well below 0.8bar (The lower limit for atmospheric pressure as defined by the ATEX Directive). The potential for an incident therefore only exists during a transient period during spin up and prior to pulling a vacuum, typically lasting less than 90 seconds.

3. All Genevac centrifugal evaporators use a condenser to trap solvent vapour. Depending on the model, this condenser will operate at between –40 °C and –50 °C. On most systems, the condenser is interlocked such that power cannot be supplied to the rotor or Infra-red lamps until the condenser is below 0 °C. The condenser can be argued to keep the vapour / air ratio low under atmospheric conditions (possibly below the lower explosion limit but this has not been proven).

4. Genevac centrifugal evaporation systems have an excellent safety record regarding fires and explosions. Between 1995 and today, Genevac have installed in excess of 1000 centrifugal evaporation systems, most of these systems remain in daily use, many are used to evaporate highly flammable solvents on a regular basis. Between them, they have amassed, by conservative estimates, more than 7 million hours of running (Q2, 2003), during which time there have been no incidents resulting in explosive ignition of solvent vapour.

5. The Genevac HT12 has been tested to determine the consequences of an explosive ignition of di-ethyl ether. This system was chosen as being representative of our systems in such a test. Following the controlled explosion of diethyl ether vapour within the chamber, no significant consequence was observed. The products of combustion escaped via the various seals on the system, particularly the windows at the rear of the machine, designed to allow IR lamp energy into the chamber. These windows harmlessly vented the majority of the gases created as a result of the reaction. The system remained intact after the test, and in fact, remained operational. The risk to the user therefore is from the escape of hot gases rather than injury from debris.

6. It would take a failure of one of the components or systems within the chamber for a potential ignition source to exist. These failures would not normally be expected to occur and this, coupled with the transitory nature of the risk as outlined in item 2 above, reduces the risk even further

7. For 3 years now, Genevac have supplied an inert purge accessory for our HT range and now our EZ-2 range of evaporators. The purpose of this is to render the internal volume of the evaporator and condenser inert before, during and after the evaporation process. It also renders the Cole pump inert during the run. The design of this system has been evaluated against the European Standard, IEC 60079-2 (Electrical Apparatus for Explosive Gas Atmospheres – Pressurized Enclosures “p”) and is considered to have met the requirements for type pz pressurizing. i.e. pressurization that reduces the classification within the pressurized zone from zone 2 to non-hazardous.

Note that this equipment was developed in response to concerns over di-ethyl ether. Other solvents may also present some risk. It is the responsibility of the user of the equipment to determine those risks, and therefore decide whether inert purging is required. Factors 1 to 6 would indicate that the risks, if present at all, are negligible. However, should concern still exist then it is possible to take advantage of the inert purge accessory, as discussed in item 7. This would render the atmosphere within the evaporator inert and remove any risk.

The present design of Genevac evaporator systems means that they are not suitable for use in any of zones 0, 1 or 2. They must therefore be used in a safe environment, such as the open environment of a ventilated laboratory or a fully-extracted fume hood.

We have also discussed the environment within the evaporator. The final decision on risk in this context has to be determined by the user of the evaporator.