Technical Blog
Rethinking EAC and HAC: Why Ventilation Design Matters
I was recently auditing a midstream facility up North. The weather was great compared to the heat and humidity that dominate Houston most of the year. I and the other audit participants inevitably talked about the weather and the differences between operating a facility in the South vs. the North. One of the differences discussed was the need for enclosing certain equipment and piping during cold winter months.
As the audit participants shared their practice of closing louvers and bay doors when temperatures dropped to freezing and below, my auditing mindset drifted to the electrical classification and ventilation system design Process Safety Information (PSI) elements of OSHA’s 1910.119 Process Safety Management (PSM) of Highly Hazardous Chemicals (HHC) mandate. More specifically, what were the electrical area classifications (EAC) and hazardous area classifications (HAC) of the areas? What supporting ventilation system design information existed to justify the EAC and HAC designations? AND, did the EAC and HAC designations along with any supporting ventilation system design information take into account the seasonal variations regarding louver and bay door open / closed status?
A handful of months earlier, I was working on a project for a lithium battery manufacturer. The electronic vehicle (EV), artificial intelligence (AI), and energy grid hardening market sectors are driving significant investment and construction of facilities that store and handle volumes of chemicals that drive OSHA 1910.119 compliance. These facilities are built and operated differently than an offshore platform or refinery or batch chemical plant. They resemble a manufacturing clean room, laboratory, assembly line, and outdoor storage / materials handling industrial chimera.
We were helping the manufacturer develop PSI for their PSM-covered areas. One area was indoors. It was a large room with multiple drop-down ventilation ducts designed to achieve a specified number of air exchanges. Within the room were several cabinets that housed piping and filters and small reservoirs. Again, thoughts of EACs, HACs, and ventilation system design information began wafting through my head regarding the difference between the open, well-ventilated room and the enclosed, poorly ventilated cabinet. What are the credible loss of primary containment scenarios in the room and in the cabinet? Where do ignition sources reside? Does the ventilation system design for the room apply to the enclosed cabinet?
When performing an audit of PSI or generating PSI from scratch, resources tend to focus on the seemingly more important PSI items, such as heat and material balances, piping and instrumentation diagrams (P&ID), relief system design, equipment design information; however, 1910.119 does not prioritize PSI – all PSI is important and safety-critical. Because of this tendency to focus on certain PSI items, some personnel may not be familiar with what goes into generating effective EACs, HACs, and ventilation system design information.
Below is a list of prompts to help ensure these PSI items are not neglected.
- Which codes and standards apply to your facility? A petrochemical facility and lithium battery manufacturing facility may need to ascribe to different sets of recognized and generally accepted good engineering practices (RAGAGEP).
- Do EAC / HAC drawings exist? Do they show the basis of classification?
- Do EAC / HAC drawings depict Class, Division / Zone, Group, Temperature Class (T-Code) as required for each discernible area?
- Have all of the Safety Data Sheets (SDS) been checked for properties such as autoignition temperatures (AIT)?
- Have all release source inventories and rates been determined?
- Have ventilation calculations been documented with accompanying equations and rationale?
- How is adequate ventilation defined and verified? Is there a ventilation system design report complete with design narratives and calculations? Information in this report may include:
- Design airflow rates;
- Dilution ventilation calculations;
- Purge / Pressurization controls;
- Make-up air sources;
- Exhaust discharge locations;
- Fan curves;
- Damper positions;
- Seasonal variances in operating conditions and enclosure conditions; and
- HVAC P&IDs.
- Does the EAC / HAC / ventilation system design information align with other PSI and PSM elements? For example, have process hazard analyses (e.g., HAZOPs, LOPAs, Bow-Ties) been informed using EAC, HAC, and ventilation system design information?
The above list is not exhaustive, but it should provide guidance to a more effective position regarding EAC, HAC, and ventilation system design PSI.
Meet the Author
John Perez – Principal Engineer
John is a chemical engineer with 25+ years of process safety and engineering experience, leading over 150 PHAs and advising clients on risk management and compliance. He is a CCPS Certified Process Safety Professional, a licensed PE, and a Sr. Adjunct Lecturer teaching Process Safety at Rice University.
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