Introduction

Many companies in Belgium and the Netherlands have their own (R&D) lab. The intrinsic chemical hazards of products are usually well known. The relatively recent modernisation of this matter, namely the introduction of REACH, has certainly contributed to a better understanding of it.

However, a risk that is regularly underestimated is the formation of an explosive atmosphere and the consequences of ignition. When working with flammable, volatile products, the necessary attention must be paid to this. In production plants and process equipment, this is usually done, but in many cases not in the laboratory.

ISMA always tries to assess installations and situations in a pragmatic way and to prescribe only sensible control measures. This article examines in a practical way the need for zoning and protection of certain lab-related equipment, in such a way that the reader can easily determine whether additional measures would be necessary in his/her company.

Chemical cabinets/Chemical safe

Question: If I have a limited storage of flammable liquids, and they are all stored in a compliant chemical locker, is an ESD and/or zoning dossier still required for that area?

Answer: ATEX 153, the social directive, states that as a company one is obliged to draw up an EDS with a zoning file when flammable products are used. Consequently, the employer is obliged to carry out a risk analysis, and in order to do this risk analysis correctly, zoning is required. A zoning report is thus an indispensable part of an ESD, and thus also a legal obligation.

The first question that arises is: Are flammable liquids being worked with? The flash point is used here, and in Belgium and the Netherlands the limit is 45°C. Above that point, zoning is usually not applied. (If working at room temperature). Let us assume that the flash point is below this temperature.

The second question then becomes: how do I do the risk analysis on such a chemical cabinet? Well, for inspiration to zoning, the NPR7910-1 can be consulted, but this is very difficult to apply to this situation. After all, what is the chance of such a bottle of product leaking, and how much would escape? It is difficult to quantify this and therefore to define a possible zone. 

In this case, the better question is: Is it completely out of the question that a bottle will leak? To put it another way: "What is the probability of an explosive mixture forming?" This is in fact the definition of zoning.

If only UN-approved packaging is used, the possibility of leaks can be excluded. However, a chemical cabinet is often used for the storage of bottles, from which they are then filled into smaller containers. And when a UN-approved packaging has been opened, the UN approval expires.

Another guideline that one could fall back on is the LQ (limited quantities) packaging regime, less than 5 litres. However, LQ requires double packaging and will therefore most likely not apply here.

The above indicates that it will be very difficult to exclude leaks completely, with 100% certainty. After all, it seems more likely that a bottle is inserted that is not sealed properly, or even worse, a packaging with a vent valve. Still not convinced: stick your nose into the chemistry cabinet. You will probably smell that the release of substances is not inconceivable. That is why we speak of a secondary source of danger, i.e. the release is unlikely, or less than 10 hours per year.

The result is therefore that zoning is required. If the story of a secondary source of danger is followed, this means a zone 2 in the cabinet. This is realistic if the cabinet has ventilation. The reason that with ventilation it still remains a zone 2 is that the ventilation can fail, and therefore vapours can accumulate. If there is no ventilation, this would even be a zone 1, with a zone 2 at a distance of 1m outside the cabinet. Imagine that a bottle of flammable product has been leaking all night and that the door is opened in the morning. The presence of an ignition source in the vicinity of the cabinet is then a potential risk. Defining a zone 2, with accompanying measures, will make this risk manageable.

As already briefly mentioned above: when zoning has been carried out, the sources of ignition must be examined. In order to check whether the explosive mixture can be ignited, it is necessary to go over which ignition sources are (or can be) present in the cupboard. (Lamp, electric pump, other electronics, etc....). The equipment in a zone must be suitable for this by means of an ATEX certification. However, a fruitless search for an ATEX-certified cabinet is often started. However, an ATEX certified chemical cabinet will not be found. Why not? Well, a cabinet is according to ATEX 114 (the economic brother of ATEX 153), not an apparatus. The reason the box is not a device: A box does not have its own energy source. (Likewise you will not find an ATEX certified silo or an ATEX certified door). However, if you hang a lamp in the cabinet, it must be in conformity with the previously determined zone.

An analogous exercise should be carried out in the room where this cabinet is located. Is there an existing risk of an explosive mixture? ISMA recommends the following approach here:

If ventilation is present in the cabinet, no external zone needs to be defined. The likelihood of ventilation failing for a long period of time and at the same time of an explosive atmosphere building up inside and leaking out through the doors, which are designed to keep dangerous vapours inside, is negligible.

If there is no ventilation, a zone 2 must be defined outside the cabinet, with a distance of 1m. This zone must also be considered upwards.

Fume cupboards/drawers

Question: I work with flammable products, do I need to purchase an explosion-proof fume cupboard?

The above question is not entirely unjustified, and is a logical reflex. An explosion in a fume cupboard is, unfortunately, not a rare phenomenon, and the high probability of proximity to a worker drastically increases the possible consequences.

 However, there are quite a few misconceptions on this subject. The most important misconception is "that an explosion-proof fume cupboard is built to limit the consequences of an explosion". The pressure in a (gas) explosion can rise to several bars, and at such pressures even safety glass will form dangerous projectiles. The only thing an explosion-proof fume cupboard does, is not to introduce additional ignition sources.

Another misconception: "The fan of the fume cupboard must be ATEX, because a flammable product is used in the fume cupboard".  If the fume cupboard is used correctly, the ventilation rate in this room is so high that the risk of an explosive mixture is negligible in most cases. The flammable gases formed are only released to a limited extent. Think for example of a distillation setup, where there is a leak in front of the cooler or a break in the cooling water. On the other hand: Pouring a bottle with flammable product into the fume cupboard is not an expected practice, and a gross overestimation of the potential leakage source.

To summarise: working with flammable products is not automatically a reason to look for explosion-proof fume cupboards. On the inside of standard fume cupboards, no electrical components are provided as standard, the lighting is protected by a thick piece of safety glass, switches are always on the outside, and all cabling is located in the double wall, shielded from the space of the fume cupboard. By the time a flammable gas reaches the fan, it is already so diluted that the concentration is far below the LEL.

How is it then that accidents still happen on a regular basis? The answer is not to be found in the fume cupboard itself, but on the outside: the user and the lack of training with regard to the specific risks of explosions. A number of common mistakes are listed below.

Cause 1: Explosions caused by a chemical reaction.

ATEX does not cover explosions caused by chemical reactions. So if a chemical reaction creates so much pressure that it leads to an explosion, an explosion-proof fume cupboard will not change this. If this cause cannot be excluded with certainty, consideration should be given to making the reaction vessel sufficiently weak, or providing it with a weak point.

In this way, the resulting pressure can be stopped by the protective wall of the fume cupboard. If the pressure in a reaction vessel cannot be guaranteed to remain low, extra measures should be taken and the strength of the fume cupboard should not be relied upon.

 Cause 2: Introduction of ignition sources

As previously stated, it is to be expected that the concentration of flammable gases will have dropped sufficiently when this gas stream reaches the extraction. However, this does not necessarily apply to the concentration of flammable gases on the working surface of the fume cupboard! Often, equipment can be found here that does not belong there, e.g. heating plates, stirring equipment, etc., and which is not ATEX-certified. These can therefore serve as an ignition source, and the permanent installation of these devices in a fume cupboard must be accompanied by the necessary risk analysis, and employees must be aware of the dangers involved. Specific attention must also be paid to flexible, movable extraction nozzles in order to extract very specifically. The combination of metal and plastics with a continuous flow of air means that they can become highly charged and cause powerful spark discharges. Therefore, always make sure that these parts are correctly and adequately equipotentially connected and grounded.

Cause 3: Introduction of other objects into the fume cupboard.

The airflow in a fume cupboard is ensured if the mobile wall is in the lowered state and if this airflow can move freely. However, a fume cupboard is often used as a mini warehouse for bottles containing flammable or toxic products. This practice impedes the intended airflow, and can even create dead zones. A secondary leak, such as a bottle that does not close properly, will now lead to accumulation and the formation of an explosive mixture, with all the risks that this entails. Moreover, in labs that are not manned 24/7, the fume cupboards are sometimes switched off at the weekend. Combining this practice with the storage of flammable products is obviously unacceptable. In summary, the following advice: only place the items required for the experiment in a fume cupboard, especially when working with (highly) flammable products.

Supplementary: The regulations for fume cupboards are described in the EN 14175 standard and translated in the NPR 4500 guideline. This contains a handy checklist for periodically checking the fume cupboard for correct operation and the way in which this check must be carried out. A correctly maintained fume cupboard is, of course, one of the basic requirements for working safely.

Conclusion

In the above text, two practical problems have been elaborated, inspired by questions and observations that ISMA regularly receives from laboratories in the business world. 

With the help of this text, you can easily check whether there is an opportunity for improvement in these areas in your company.

Legislation

This article does not always refer directly to legislation or standards. However, the system as discussed is supported by the ATEX legislation and related standards.

Finally

This article does certainly not cover all possible explosion hazards in a laboratory environment, but only elaborates on two frequently occurring examples. However, if you have questions about a specific application, ISMA can always advise you.