What is Hazardous Area Classification (HAC)?

Hazardous areas are places in an industrial facility that can create an explosive atmosphere due to the presence of flammable gases, liquids, vapours, dusts, and fibers, both under normal and abnormal operations.

Hazardous Area Classification, more commonly known as HAC, is a method for evaluating the possibility of a flammable environment emerging and how long it might persist. It is a comprehensive assessment of a site's possible electrical dangers, such as flammable mist, vapors, and fumes, as well as combustible dusts and fibers.

Why is HAC necessary?

According to the Law on Fire Prevention and Fighting implementation records of the Ministry of Public Security of Vietnam, from 2012 to 2022, 8,580 fires happened at warehouses, manufacturing factories and business offices which accounted for 29% of fires nationwide. This is an alarming number and is proof that it is time for businesses to take crucial measures to improve fire safety at their workplace, especially in factories and warehouses.

By including HAC facilities, it directly affects the effectiveness of fire and explosion prevention.

Some significant benefits of HAC are:

• To locate and classify specialised areas containing materials that can lead to fire, explosion, or other dangerous incidents;

• To meet the requirements of the Technology Safety System (PSM);

• To facilitate the selection and installation of appropriate equipment for safe use in zoned areas;

• To take measures to reduce the risk of fire and explosion and keep the working environment safe.

What is the HAC service?

The HAC service identifies locations that are susceptible to fires or explosions, assisting industries in minimising their risks of encountering an incident that results in property damage, potential injury, or loss of life.

The HAC layout facilitates the selection of appropriate equipment and installation processes to ensure that the equipment operates safely in its environment and does not cause fires or explosions. Hazardous area categorisation layouts are often created by a team of Process Safety Electrical and Instrument engineers, with assistance from plant operations and Health, Safety, and Environment (HSE).

General Methodology:

Explosions are sudden with huge speed and fast occurring oxide reactions which generate a temperature and pressure increasement. Most well-known are reactions of flammable gases, vapours or dust together with oxygen out of the air.

As a rule, for explosions to happen in atmospheric air, three factors must be present at the same time:

• flammable material
• oxygen (air)
• source of ignition

Removing either the fuel or the ignition source dramatically reduces the probability of a fire. However, for any given industry involving hazardous materials, many of the process materials may include those whose physical properties will result in oxidation (will burn) if permitted to collect in the air. Additionally, there may be permanent ignition sources present in the form of electrical equipment utilized for process controls, lighting, motors, etc. as well as hot surfaces. To have a significant impact on reducing the potential to create an ignitable spark or flame, the electrical equipment must be suitable for the process materials being handled. Generally, different process materials and process operations will have different electrical equipment designs.

HAC is a very effective ignition control means. Hence, the action for performing and documenting the HAC is not only required by many codes, standards, practices, and legal legislative actions, but is also required to be kept current. Since HAC is a requirement, the effective time to conduct the analysis is when information on the materials present is known and when the process operation has been established. This is the minimum information necessary to identify the electrical/electronic devices and hot surfaces present. For existing operations, many guidance documents will suggest including HAC reviews with any Management of Change (MOC) that involves replacing or installing equipment and/or new electrical devices.

HAC Execution Steps

The following are best practice execution steps to address the HAC assessment:

1. Identify Release Sources:

• Inputs: Piping and instrumentation diagrams (P&IDs), plot plans, heat and material balance data, and workshop information.
• Activity: Identify potential sources of hazardous releases within the facility or process.
• Outputs: A list of identified release sources.

2. Determine Grade of Release:

• Inputs: Information about the identified release sources.
• Activity: Assess the likelihood and severity of each release, classifying them into different grades based on their potential impact.
• Outputs: A classification of the release sources based on their grades. The design may be amended to remove continuous or primary sources of release.

3. Determine Fluid Category:

• Inputs: Physical properties of the released substances, heat and material balance data, and Material Safety Data Sheets (MSDS).
• Activity: Classify the released fluids into different categories based on their flammability, explosivity, and other hazardous properties.
• Outputs: A classification of the released fluids into appropriate categories.

4. Establish Zone Classification:

• Inputs: Ventilation data and information about the facility's layout and processes.
• Activity: Determine the appropriate hazardous zones based on the likelihood and persistence of flammable or explosive atmospheres.
• Outputs: A classification of the facility into different zones (e.g., Zone 0, Zone 1, Zone 2) based on the level of hazard.

5. Hazardous Radius:

• Inputs: Air dispersion modeling data.
• Activity: Calculate the radius around each release source within which a hazardous atmosphere could exist.
• Outputs: Determination of the hazardous radius for each release source.

6. Hazardous Area Classification Drawings:

• Inputs: All the information gathered in the previous steps.
• Activity: Create detailed drawings that show the classification of the entire facility into hazardous zones.
• Outputs: Hazardous area classification drawings that can be used for safety planning and design.

This systematic workflow helps ensure that hazardous areas are properly identified, classified, and managed, minimizing the risk of accidents and ensuring the safety of personnel and equipment.