A Brief History of H.A.C


The history of Hazardous Area Classification starts in the 18th century when the demand for energy to power the industrial revolution, and the growing demands of technology required the development of the coal mining industry. These early mines were notorious for releases of firedamp gas (methane) which would cause fires and explosions when ignited by a flame or spark.

Note that the first ‘firemen’ were miners sent into early mines at the start of a shift to deliberately ignite firedamp that may have accumulated. This was a very dangerous job but necessary at the time as the only light sources available underground were naked flames.

As electricity became more readily available for communication, light and power within the mines, the mining industry supported research into the ways to avoid igniting the flammable atmosphere that was expected to occur. This improved our understanding of the basic properties of flammable materials (gas and coal dust), improved ventilation techniques to minimise gas accumulation and developed ways to prevent ignition by electrical equipment. This was associated with the development of codes and standards which codified a standard approach to the associated safeguards.

IPS-front-screen Ad: Process Safety E-Learning (ICHEME Approved) From $97 USD




Over time, these safeguards were also applied to above-ground facilities where the presence of flammable materials was creating similar risks of fire and explosion (oil, gas, petrochemicals, etc). The open nature of above-ground installations led to the concept of a hazardous area, within which a release of flammable gas/vapour might create a flammable atmosphere before dissipating. This flammable atmosphere requires that the local electrical equipment should incorporate appropriate safeguards against ignition.

Initial attempts to codify the level of risks of fire or explosion focused on the potential for electrical ignition and the associated safeguards. The flammable atmosphere is split into different Zones based on potential likelihood and duration. The Zone extents were largely based on qualitative assessments for typical flammable materials in specific applications (such as storage of petrol in cylindrical tanks) by a committee of experienced engineers. These assessments were deliberately conservative as a quantifiable estimation methodology was not available at that time. The cost of significant consequences outweighed the benefits of using a smaller hazardous area extent.

From the 1990s, significant developments in computer modelling, particularly CFD, and validation by improved research techniques have advanced the understanding of dispersion local to the release point. By the mid-2010s, further research led to internationally recognised codes and standards (IEC, EI15, etc.) incorporating improved, scientifically based correlations for estimating hazardous area extents. risk assessment and material flammability from ‘first principles'.

Hazardous area classification has come a long way from its roots in the coal mining industry. Now, with a better understanding of material properties and the application of advanced modelling techniques, we can quantify those zones where certified equipment is required to minimise the risk of igniting a flammable release, contributing to the creation of a safer workspace for people operating at facilities using flammable and combustible materials.