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Hazardous Area Classification
The process of Hazardous Area Classification (HAC) may be done in two basic methodologies i.e. direct example or based on a calculation. Both of these methods are complemented with a risk assessment. In some cases the HAC may be done with only a risk assessment but it is the same with the case of direct example where the result depends a lot on opinions and without the help of a Subject Matter Expert (SME) results in over or under classification. The ExHACT method of HAC results in a defendable classification and as per legislation is traceable. The following process is used and described in short.
Team - Compilation and appointment of a team for the HAC study. This will as a minimum include a production or process person, an engineering person and a Subject Matter Expert (SME). The SME is the ExHACT representative and will facilitate the process.
Chemical Properties - Properties of all chemicals used in the area are defined and listed. The physical properties are added and the flammability of each chemical is calculated. As most chemicals are a composition of other base chemicals the process of defining the physical properties of each composition is scientifically calculated. Operational and meteorological effects are included so that the chemical properties used is the same as experienced in the actual conditions.
Operational Properties - The operational properties are defined in terms of pressures, temperatures, height above, and level or volume changes are defined and listed for each chemical. The operating envelope and Process Flow Diagram (PFD) is utilised for this.
Meteorological Conditions - Properties like altitude, wind speed and direction, ground and obstruction levels, radiation, barometric pressure, ambient air temperature, land surface temperature, precipitation, evaporation and solar radiation are all used as effects to the HAC.
Sources of Release - The flammable chemicals are then implanted onto the Mechanical Flow Diagrams (MFD) sometimes called the Process and Instrumentation Diagrams (P&ID). Every possible source of Release (SOR) is defined and listed. This would include any seal, vent or open surface for example.
Dispersion Calculations - The dispersion of the gas, vapour, liquid, dust or any combination is then calculated using a number of standard formulas or making use of a Computational Fluid Dynamic (CFD) application.
Classification Report Review and Approvals - The end result of the above is a HAC report and includes a number of items as required by Legislation for example 60079-10-1. This report has to be approved by the legally appointed Occupational Health and Safety person as well as the Machinery Safety person. As soon as the approval is done the drawings can be completed as a spatial view of the result of the HAC study.
Hazardous Area Classification Drawings - The preparation of the HAC drawings must be done so that the end result is usable. In most cases the drawings do not define a clear indication of the HAC results. Large areas are classified as the worst case and this costs money for the final Explosion Protected Equipment (EPE) used in the area. ExHACT has developed an appropriate drawing model that is complete and provides the required detail for the selection, installation and inspection of Explosion Protected Equipment (EPE). This drawing also facilitates the writing of a Certificate of Compliance (COC) for the Electrical Installation.
Review and Approval of Drawings - The final drawings are then approved by the same team that has prepared the HAC study.
The end result of the HAC is the selection, installation and inspection of the installation. In the case of current installations that require a review of the HAC of the installation the result of the HAC process is the inspection and review of the compliance of the installation and then the application of corrective actions.
Experience shows that many installations do not have the required HAC documentation and even if they have documentation something has changed that influenced the installation. Any changes for example adding of a source of release, changes in pressure or chemical composition and even operational changes like flaring only on startup will affect the HAC results. All of these changes must be managed through an official Management of Change (MOC) process that will facilitate the review and update of the HAC.
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