February 2019

Environment and Safety

Hazardous area classification compliance: Focus on communication

On November 30, 2013, an explosion and fire occurred at the UCB Farchim SA site in Switzerland. Fortunately, no injuries or fatalities occurred.

Johnston, J. E., Eccleston, C. A., Bath Process Safety Management

On November 30, 2013, an explosion and fire occurred at the UCB Farchim SA site in Switzerland. Fortunately, no injuries or fatalities occurred. The source of the explosion was an electrical connection located in the basement of a building, so the physical damage was extensive. According to Eric Fumière, UCB Risk Manager, “We learned many lessons. For example, the electricity network should be located outside of the building. It seems elementary, but the fact that ours was located inside means the initial explosion caused heavy damage even before the fire.”1

FIG. 1. HAC process.
FIG. 1. HAC process.

Incidents like this bring process electrical safety to the forefront of process safety management (PSM). The standard for Process Safety Management of Highly Hazardous Chemicals, 29 CFR 1910.119 ("PSM standard") was issued in early 1992 and became law in the US. This Occupational Safety and Health Administration (OSHA) document identified “electrical classification” (hazardous area classification) as required process safety information (PSI) for covered processes. OSHA requirements included not only that a hazardous area classification (HAC) be assigned, but also that a study be conducted to verify compliance of installed electrical equipment to the assigned HAC.

In this article, a process is presented for determining an HAC and developing a remediation plan following an HAC compliance assessment study. The importance of a team approach to enhance communication in applying HAC information and utilizing HAC documentation effectively is also discussed.

Intent and focus

The intent of HAC is to minimize electrical energy as a potential source of ignition due to a non-catastrophic release of flammable or combustible materials in a classified area. Results of an HAC assessment (area classification, material group, and Temperature Class (T Code)/ignition temperature) are used in the design, selection, construction and operation of electrical equipment and electrical systems to ensure this aspect of process safety is addressed. The National Fire Protection Association NFPA 70 National Electrical Code (NEC) covers requirements for electrical installations classified as hazardous due to materials handled, processed or stored in those locations.

Properties of materials handled in process equipment or an area under study set its classification per NEC Article 500, “Hazardous (classified) locations, Classes I, II and III, Divisions 1 and 2,” 500.5(A) Classification of Locations. Materials can be gas, liquid-produced vapor, liquid or solid, and the classes are defined as follows:

  • Class I (gases and vapors)
  • Class II (dusts)
  • Class III (fibers/flyings).

This article focuses on Class I and Class II materials, due to their prevalence in industry, and excludes Class III materials.


The overall process steps in assigning an HAC and determining compliance vary slightly, but they can be generally defined (FIG. 1).

The steps shown in FIG. 1 present a process that begins with first assigning HAC to a location and concluding with a remediation plan to address any findings identified in the HAC compliance assessment. Activities for each step are outlined here to assist in establishing the inputs and outputs as groundwork for later discussion.

Step 1: Set scope and perform HAC assessment study

The scope of an HAC assessment study determines the location, quantity and type of equipment, as well as the methodology of how an assessment will be performed. Steps for completing an HAC assessment are prescriptive and should be based on requirements given in both company standards and applicable, recognized and generally accepted good engineering practices (RAGAGEP). Two main RAGAGEP for Class I materials are NFPA 497, “Recommended practice for the classification of flammable liquids, gases or vapors and of hazardous (classified) locations for electrical installations in chemical process areas”; and API RP 500, “Recommended practice for classification of locations for electrical installations at petroleum facilities classified as Class I, Division 1 and Division 2.” A RAGAGEP for Class II materials is NFPA 499, “Recommended practice for the classification of combustible dusts and of hazardous (classified) locations for electrical installations in chemical process areas.” Consideration should also be given to RAGAGEP for facilities or sites located outside the US, such as IEC 60079-10-2, “International standard explosive atmospheres—Part 10-2: Classification of areas—Explosive dust atmospheres.”

Material properties must be known to properly complete Step 1 for both gases and vapors and combustible dusts. For a gas and vapor, its composition, operating pressure and temperature, and auto ignition temperature determine its hazardous area classification, as well as its material grouping and temperature class (T Code) designation. For a combustible dust, its dust cloud minimum ignition temperature (MIT), dust layer MIT, dust cloud minimum ignition energy (MIE), bulk dust resistivity and presence of dust layers on horizontal surfaces are used to determine its material grouping and classification. Therefore, a methodology to perform an HAC assessment study is all about the material being processed (the process) and whether it is flammable or combustible if a non-catastrophic release occurs. All proper HAC methodologies must utilize properties of the material in the location under study. This requires careful study for both Class I and Class II materials.

Most process streams in refineries, chemical plants and petrochemical facilities are complex mixtures requiring analysis of multiple components. Many manufacturing processes have a combination of gas, liquid-produced vapor, liquid or solid materials requiring application of several RAGEGEP to complete the HAC assessment.

The HAC assessment report provides two key benefits to the user of PSI. First, the HAC report contains source information for how and why the equipment shown on the HAC drawings are classified. Secondly, the HAC report contains the classification results for each piece of equipment, making it easier to determine whether process changes will impact the HAC. Leveraging the HAC report in combination with a site’s management of change (MOC) process assists in meeting OSHA’s requirement that all PSI remain evergreen.

Step 2: Issue completed HAC study and documentation (report and drawings)

A report and an associated set of drawings are the preferred means to document the results of an HAC assessment study. This documentation (at a minimum) should include the following:

  • The basis for determining the HAC assessment results
  • Drawings referenced to the unit or area plot plan
  • Drawings showing both the plan and elevation views
  • The area classification and material grouping
  • The temperature class designation (Class I material) or ignition temperature (Class II material).

The report contains a description of methodology used in the study and references sources for process-related information used. This report details how and why the area classification was determined and gives an overall temperature class (T Code) designation for Class I materials, or ignition temperature for Class II materials for the location. The report should provide the classification and hazard radius, as well as material grouping for each point source within the scope to link study results to information displayed on the drawings. A drawing set typically includes location plans, elevations, details, tables, notes and legends to properly document the results of the HAC study. Drawings present assigned class, division, material grouping and hazard radius (if applicable) for each point source of emissions. Housekeeping measures or additional information used to determine the classification for equipment handling a combustible dust should also be documented.

Step 3: Conduct HAC compliance assessment using standards and code requirements vs. HAC documentation

An HAC compliance assessment for a unit or area focuses on visible process electrical equipment and electrical installation practices. It is a gap analysis between both code requirements and other recommended practices or guidelines vs. the latest version of HAC documentation. In other words, this activity compares what is there to what is supposed to be there. Scope is set for the HAC compliance assessment by first determining what will be included and what will be excluded, and then listing specific parameters or assessment bases for the assessment team. For example, a building containing online process analyzers for flammable or combustible materials should be included. Conduit systems transitioning from below to above grade that contain grounding and cathodic protection conductors could be excluded if no associated electrical-arc-producing devices are present. Personal safety guidelines are also noted, such as limiting access to only those structures with dedicated stairs and handrails. A format for the communication of any findings, such as photographs or a checklist in electronic format, is also established so the assessment team is prepared. A physical walkthrough of the area allows the assessment team to visually confirm compliance and note any instance of noncompliance.

Step 4: Issue HAC compliance assessment report with findings

Results of the HAC compliance assessment are issued in a report that documents the area, buildings and equipment within the scope and presents the findings in the format as set in Step 3. Findings can be categorized as “specific” and listed with a unique number for each piece of electrical equipment or electrical installation practice, as well as “general” or “systemic,” which are applied to the overall area assessed. Clear wording is important to communicate the exact case of noncompliance found. The same piece of electrical equipment may have several findings, each of which stem from a unique noncompliance to code, and each finding should be noted separately within the results.

Step 5: Issue remediation plan for HAC compliance assessment findings

A remediation plan for the HAC compliance assessment findings provides an opportunity for the assessment team to make its final recommendations. Many findings may have simple solutions to bring the installed electrical equipment or associated electrical installation practices into compliance. Some findings, due to electrical equipment accessibility or label illegibility, require further investigation to determine whether a noncompliance situation exists. Still other findings have complex solutions that may require detailed engineering designs to remediate. A remediation plan can include recommendations for findings that encompass all or some of these categories. In each case, however, a detailed review of the remediation plan by those individuals responsible for the design, operation and maintenance of the electrical equipment assessed is highly recommended.


The NEC states, “All areas designated as hazardous (classified) locations shall be properly documented. This documentation shall be available to those authorized to design, install, inspect, maintain or operate electrical equipment at the location.”2 This formally sets in place the team membership that should routinely use HAC information to safely implement electrical equipment and electrical system changes in a production unit. This team membership could include personnel from process engineering, project engineering, maintenance, mechanical integrity, operations and construction charged with a common goal of sharing and using the latest HAC information available. Issuing the latest HAC information as formal record documents is critical, but a key to the team’s success is utilizing it effectively.

With HAC information available and the team in place, why do questions and confusion frequently arise regarding compliance with the assigned classification? Several factors can contribute to this, but they center on the HAC documentation itself. In the authors’ opinion, the major issues associated with using HAC documentation can be broken into three problem areas:

  1. Lack of understanding
  2. Lack of knowledge
  3. Lack of utilization.

These problem areas can be exhibited by some individuals but are more often displayed by the entire team. While these problem areas exist, they can be addressed by taking a more focused team approach, as the following discussion shows.

Lack of understanding

The first area is a lack of understanding regarding what should be included in HAC documentation. Although information was presented in Step 2, further discussion is required. An HAC assessment report covers the technical aspects of how the classification was determined and should be available if background information is required. A report, however, is not normally used in the field for obtaining details of the assigned classification. Drawings are important since they should be considered as “at the point of use” or quick reference documents, and should be a priority for record documents associated with area classification.

FIG. 2. Example of HAC information utilization process.
FIG. 2. Example of HAC information utilization process.

Two main reasons exist for why drawings should be the focus of HAC documentation. First, the NEC states, “One type of documentation consists of area classification drawings. Once the hazardous area has been classified and the hazardous area documentation has been developed, the materials and installation methods of the NEC are used to safely construct the electrical system in the classified area. This approach provides the necessary information for installers, service personnel and the authority having jurisdiction (AHJs) to ensure that electrical equipment installed in classified areas is of the proper type.”2 The NEC calls out responsible parties as not only those individuals who install the electrical systems, but also the service personnel and those with the AHJ for the classified location. Although a legal term, one definition for AHJ, is “a person who has the delegated authority to determine, mandate and enforce code requirements established by jurisdictional governing bodies.”3 The intent of the NEC as stated should be viewed as a shared mission by many individuals to ensure that HAC compliance is maintained.

The second reason drawings should be the focus of HAC documentation is that they are a recognizable medium for individuals in a plant or facility. Technical drawings are used during all phases of project development and are central to communicating many types of process safety information. The format of the HAC drawings should allow all team members, from an electrician assigned to install new equipment in the field to a project engineer assigned to design an upgrade to an existing electrical system, to obtain all HAC information efficiently. The key is to have all required information clearly shown and the document readily available when needed.

The purpose of HAC drawings, then, is to provide the team with information to ensure that electrical equipment and electrical system changes are conducted in compliance with the assigned classification, material grouping and temperature class (T Code)/ignition temperature designation. Lack of understanding as a problem area will be addressed if all team members can correctly read and interpret HAC drawings and can readily obtain the required information.

Lack of knowledge

The second problem area is a lack of knowledge regarding how and when to revise HAC documentation. Since OSHA considers HAC as required PSI for all covered processes, specific documentation steps must be followed:

  • The documented results must be based on the process technology and materials used in the unit.
  • The area classification documentation must be kept “evergreen.”
  • This “evergreen” state of documentation is to be maintained using the MOC process, PHA process, and company-specific document control standards and procedures.

The team involved in the use of the HAC documentation will usually be involved in supplying process information needed for the assessment study, as described in Step 1, or may even perform the HAC assessment itself. The team should follow closely the dictates of site or facility management to create documentation that contains the modified HAC-related PSI without burdening the document control process with unnecessary content. Maintaining “evergreen” HAC reports and drawings are critical for the team to manage this aspect of process electrical safety.

Other benefits include understanding, as well as communicating, upcoming changes for a process unit that can impact material grouping and temperature class designations. If the document control methodology includes these components, then the problem area of how and when to revise HAC documentation has been addressed.

Lack of utilization

The third problem area is the lack of utilization of HAC information, both in updating PSI and in the process safety risk assessment process. Typical activities that routinely use HAC information in a production facility are shown in FIG. 2, which reinforces the need for communication between team members in applying HAC information. Reports and drawings that document the HAC assessment basis and the assessment results can provide key information, including:

  • The process technology and materials documented for the production process are also used for the HAC assessment study.
  • The HAC documentation should be used to support process safety risk assessments, such as PHA studies, MOC evaluations and building siting studies.
  • HAC drawings show the potential for a non-catastrophic release of flammable materials
    and provide the classification (class and division), material grouping, and temperature class (T Code)/ignition temperature designation for the location.
  • HAC information sets the design criteria for electrical equipment and electrical equipment installation requirements.

A major barrier to communicating HAC assessment results is removed once team members understand how this PSI is linked between their individual tasks and areas of responsibility. This encourages team ownership of the HAC information flow, and addresses the problem area associated with the lack of utilization of HAC information.

Takeaway. Every day, changes are made in production facilities worldwide. Physical equipment changes can impact the equipment layout of a production unit requiring communication to ensure those individuals impacted are made aware. Changes in operating procedures and training, updates to PM schedules and updates to other PSI documentation are but a few of the documents typically affected by such changes. Effective use of HAC information plays a key role in process electrical safety, and a team approach lies at the heart of managing, applying and updating this HAC information. Information in the hands of a few limits the ability of this team to play a proactive role in the management of process safety. Clear communication should not only be a goal, but a key step in engaging this team in using HAC information efficiently and effectively. HP


  1. “Allianz Global Corporate & Specialty Global Claims Review 2015: Business Interruption In Focus,” December 2015, http://www.agcs.allianz.com/assets/PDFs/Reports/AGCS-Global-Claims-Review-2015.pdf
  2. 2014 National Electrical Code, Article 500 Hazardous (Classified) Locations, Classes I, II and III, Divisions 1 and 2, 500.4 General. (A) Documentation.
  3. Authority having jurisdiction (AHJ), http://www.dictionaryofconstruction.com/definition/authority-having-jurisdiction-ahj.html

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