Does any part of your site contain any portions that could be considered Hazardous Areas?
By Brad Guy
Defining Hazardous Areas
Firstly, we need to define what a Hazardous Area is, and AS/NZS60079.10.1 explains this:
AS/NZS 60079.10.1:2009 (+A1)
The objective of this Standard is to set out requirements for the classification of areas where flammable gas or vapour risks might arise, in order to permit the proper selection and installation of equipment for use in such hazardous areas. This Standard is for the use of manufacturers and installers of equipment as well as by inspecting authorities.
It is intended to be applied where there may be an ignition hazard due to the presence of flammable gas or vapour, mixed with air under normal atmospheric conditions (see note4 below), but it does not apply to
a) mines susceptible to firedamp;
b) the processing and manufacture of explosives;
c) areas where a hazard may arise due to the presence of ignitable dusts or fibres (refer AS/NZS 61241.10)
d) catastrophic failures which are beyond the concept of abnormality dealt with in this standard (see note 5);
f) domestic premises.
Note 4 - Atmospheric conditions include variations above and below reference levels of 101,3 kPa (1 013 mbar)and 20 °C (293 K), provided that the variations have a negligible effect on the explosion properties of theflammable materials
Note 5 - Catastrophic failure in this context is applied, for example, to the rupture of a process vessel or pipelineand events that are not predictable
3.3 Hazardous area (Definition)
an area in which an explosive gas atmosphere is or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of equipment
Explaining Flammable Atmospheres
By the explanation and definition above, Hazardous Areas (in relation to explosive atmospheres) are areas where the prospect of a flammable atmosphere developing through gasses (or combustible dusts as per AS/NZS 60079.10.2) “may be expected” in quantities that could cause a fire or explosion if an ignition source is present.
If we look at the fire triangle it shows that three elements need to be present to create a fire or explosion:
As mentioned above, Hazardous Areas can only be “classified” at what is considered normal temperatures and at atmospheric pressure. So basically, the fire triangle depends on there being 21% oxygen in the air and a flammable mixture.
All flammable material will have an explosive range that will sustain combustion – that is to say, it is to be mixed with air in certain proportions above the Lower Explosion Level (LEL) and below the Upper Explosion Level (UEL) to form an explosive mixture. Some examples are given below:
It can be seen from the table above that different chemicals can have varying ranges of an explosive range.
Mixtures below the LEL means the mixture is too lean to ignite, not enough fuel and with mixtures above the UEL they are too rich to ignite, so there is too much fuel to ignite the mixture (flooding).
So theoretically as a flammable gas is released from a source very close to the source will more than likely be above the UEL and difficult to ignite, while the further away you get the easier to ignite until you get beyond the LEL and there is not enough gas to ignite.
Introducing Sources of Ignition
The only element left to introduce is a source of ignition. These sources of ignition can be created from many different sources. Some basic sources are shown below; -
ANY electrical equipment that is not certified to be installed in the hazardous area, including:
Portable, transportable and personal electrical equipment
Car key remote controls
Equipment and actions that heats up with friction
Equipment and actions that create sparks
Concentrated lasers can be an ignition source to some flammable or combustible material
Untrasonics can be an ignition source to some flammable or combustible material
Where can these flammable gases (or combustible dusts) be found in industry?
Flammable gases and combustible dusts can be found in many and varied industries, some examples obvious – others not so obvious. Insurance companies are very aware of hazardous areas and the need for compliance and safety.
Some examples are shown below:
Gas drilling and processing both on shore and offshore
Coal mining both underground and surface
Manufacturers of crop protection products (Combustible organic dusts)
Bakeries (combustible organic dusts such as flour etc)
Sewage treatment plants
Coal or gas fired power stations
Pet food manufacturers
The problem is less needing to know IF you have any Hazardous Areas within your industry, but rather WHERE ARE THEY? As shown in the above list, it covers a vast array of industry and most industrial plant will have some form of Hazardous Area in places.
It only takes an ignition source to start a fire or explosion that could cause injury, death and major damage to plant and disruption to the process.