Electrical Area Classification in Biotech Manufacturing Facilities: Part Two

In short, manufacturing facilities for the biotech and pharmaceutical industries commonly involve the use of flammable gases, flammable liquid-produced vapors or combustible-produced vapors. These are present or introduced at different stages of a process, commonly referred to as either open or closed.

Electrical area classification is defined by four components: Class, Division, Group and Temperature code. Here’s a concise definition of Electrical area classification using its four components:

• Class: The broad environment type in which flammable or hazardous atmospheres may be present (e.g., Class I for flammable gases, Class II for dusts, Class III for fibers).
• Division: The level of confinement or likelihood of an explosive atmosphere being present (Division 1: present under normal operation; Division 2: unlikely and only during abnormal conditions).
• Group: The specific substance category within the Class (e.g., Group A, B, C, D for Class I gases - A is acetylene, B is hydrogen, C is methane, D is propane - different classes use different groupings for dusts and fibers).
• Temperature code: The maximum surface temperature that equipment can reach without igniting the surrounding atmosphere, used to select equipment with appropriate thermal protection.

The terms open and closed relate to the “Division” component only, and that component is further broken down into Division 1 and Division 2. Open is equated to Division 1 and Closed to Division 2.

That’s a lot to take in at a glance. So, what specifically do these terms mean as they relate to electrical area classification? Let’s look at each individually.

Open and Closed process: An Overview

The term open is a short descriptor for a three-part definition of Division 1 that can be found in the electrical code (National Fire Protection Association 70 500.5 (B)). This is also true for the term closed.” Open and closed do not, however, have written definitions within the electrical code.

Division 1 (Open) has the following characteristics:

• Cases in which ignitable concentrations of flammable gases or liquid-produced vapors can exist under normal operating conditions
• Cases in which flammable gases or vapors may exist frequently because of repair or maintenance or because of leakage
• Cases in which breakdown or faulty operation might release ignitable concentrations and might also cause failure of electrical equipment that would directly cause the electrical equipment to become an ignition source

Division 2 (Closed) has the following characteristics:

• Cases regarding locations where volatile flammable gases or liquid-produced vapors are handled, processed, or used. The gases or vapors will normally be confined within closed containers or closed systems from which they can escape only due to accidental rupture or breakdown or in case of abnormal operation.
• Cases in which ignitable concentrations of flammable gases or liquid-produced vapors are normally prevented by positive mechanical ventilation—and which might become hazardous through failure or abnormal operation of the ventilating equipment.
• Cases of locations adjacent to a Class I Division 1 location. In such locations, ignitable concentrations of flammable gases or liquid-produced vapors might occasionally be communicated, unless it is prevented by adequate positive-pressure ventilation from a source of clean air—along with effective safeguards against ventilation failures.

The electrical engineer works with the process subject matter expert, with input from process operators when available, to define a basis and identify the source points needed to develop the electrical area classification. The electrical engineer is most often the responsible individual and engineer of record for the electrical area classification documentation.

An Example of Open and Closed Processes: The Fume Hood

One of the more common applications of flammable gases and liquids in the biotech and pharmaceutical industries involves the fume hood. The fume hood is intended to protect personnel from exposure to flammable vapors, and to limit the electrical area classification spill.

This following example reviews open processing and closed processing inside a fume hood.

Open Processing: Flammables are processed inside a fume hood, where at some point the container or vessel holding the flammable is opened. This condition is an open process and exposes the flammable liquid. Vapors associated with that flammable liquid are allowed to escape (liberate) from the container or vessel and begin mixing with the surrounding air. Mixing with air presents a potential for a flammable vapor mixture to be present in air under normal conditions.

The fume hood takes clean air in from the surrounding space and exhausts that air, now mixed with a flammable vapor, to the outside by venting to a stack on the roof.

Because there is an open process inside the fume hood, the electrical area classification within the fume hood enclosure is categorized as Class I Division 1. The fume hood enclosure becomes the boundary, and the Class I Division 2 area spills into the surrounding space.

The vent that exhausts the flammable vapors from the fume hood includes a Class I Division 1 bubble, surrounded by a Class I Division 2 bubble. These bubbles are measured from the top vent opening. The stack is 10 feet above the roof, and the electrical area classification typically has no impact, since there are no electrical or electronic devices within this area.

Figure 1 provides details for the electrical area classification, based on open processing inside the fume hood—along with the vent discharging upward.

Closed Processing: Flammables are processed inside the fume hood without exposing the flammable liquid. This can be accomplished by a number of methods. One method is a pressurized container of flammable liquids, and no-drip hose connections used to transfer the flammable liquid into a vessel for processing. The hoses are blown clean with nitrogen and the vessel is not opened. The flammable liquid is never exposed during the transfer. Only a failure of some kind will result in flammables being present inside the fume hood.

As described in the “Open Processing” section above, the fume hood takes clean air in from the surrounding space. The exhaust is vented through a stack on the roof.

Because the process remains closed inside the fume hood, the electrical area classification within the fume hood enclosure is Class I Division 2. The fume hood has adequate negative pressure preventing flammable vapors from communicating with the surrounding space. The edge of the enclosure is then the boundary. There is no further spill of the classification into the surrounding space.

There is no differentiation made in NFPA 30 Table 7.3.3 Electrical Area Classification with the vent discharging upward between open and closed processing. The vent that exhausts the flammable vapors from the fume hood includes a Class I Division 1 bubble, surrounded by a Class I Division 2 bubble measured from the top vent opening.

Figure 2 provides details of the electrical area classification, based on closed processing inside the fume hood.

The first two installments of this series explored electrical classifications in biotech and pharmaceutical laboratories. The next and final installment will look at solutions to address electrical area classification requirements when transitioning from a research and development environment to full manufacturing.

View Electrical Area Classification in Biotech and Manufacturing Facilities: Part One