Mention the words “Hazardous Area Classification” and most people who operate plants think, “Oh No! It means that I have to install explosionproof equipment.”
Well, nothing could be further from the truth. First of all all hazardous areas do not have explosionproof equipment (it is just one of the many ways in which one can implement protection in hazardous areas-other means like increased safety or purging can also be used-but that’s a matter for another post altogether!).
The point I am making here is that not all areas of a plant that process hazardous materials need be classified as hazardous. Hence, one must carry out a hazardous area classification exercise, not only during the design of the plant but also subsequently at intervals of one to three years.
This hazardous area classification exercise, if done correctly, can not only decrease the costs of operating plants that process solvents, explosive vapors and gases and similar materials, but also significantly reduce the chances of an accident from happening.
How can that be?
In any process plant that processes hazardous materials ( those that are potentially explosive or inflammable), there are some places, where these materials are very likely to be present and in other places, least likely to be present. Even in places where these materials are present in large quantities, it does not mean, that they can burst into flames anytime (for example, one may have thousands of gallons of Acetone, a highly inflammable liquid in a storage tank, but it may have a Nitrogen blanketing over it, so no chances of it ever catching fire). Thus, if one does a study of the various areas in such plant, that could be hazardous, one will find some areas with more likelihood of fire/explosion, some with lesser likelihood of the fire/explosion and other areas with a very very little chance of ever bursting into flames. Based on this, we can classify such areas as Division 1, Division 2 and Safe areas. If we use the IEC system then we have the classification as Zone 0, Zone 1, Zone 2 and safe.
(Note: I admit, the above is a very simplistic description of area classification. If you wish to know about this in more detail you can find a comprehensive training course on Hazardous Area Instrumentation here, that covers a lot of this stuff . Also you can take a look at the Hazardous Area Classification ebook here, a free trial can be downloaded from the link)
Nitrogen blanketing is one way of reducing the classification of an area. Another cheaper and far more simpler way for reducing the degree of classification, is the ventilation. For example if an area of a production building of a plant, does have some vessels having some hazardous liquids, but if the area is very well ventilated by having something like huge exhaust fans and blowers in it ( implying that the fumes that are explosive, will be easily dispersed outside), then the area classification can be reduced (say from a Division 1 to Division 2 OR from a Division 2 to a Safe Area). However, there is a catch. The conditions, under which this area classification was done, MUST NOT CHANGE and these conditions must be communicated to the personnel who operate the plant.
If this is not done, then disaster may loom. Have a look at a real life case, where a worker switched off a ventilation fan, in a plant building. The fan was very important in carrying away explosive fumes from inside the building to outside. The US Chemical Safety Board has made a video of this case study and posted it on their website as well as on YouTube.
You can view the video below and draw your own conclusions.
Our conclusion is simple. If the area classification has been done, with certain assumptions or conditions, then the shopfloor workers must be knowing about it. If these conditions are changed, then the original area classification done becomes NULL and VOID. If this is not understood by all and sundry, then disasters may occur.