Gas cabinets and exhausted enclosures are found in many of our client’s facilities, primarily in semiconductor fabrication and research laboratories. The appropriate amount of airflow is not always obvious to the designer. This blog is the third in a series of three that will focus on code requirements and ventilation rates for gas cabinets and exhausted enclosures associated with compressed gases and their distribution.
Part 1: Ventilation of Gas Cabinets and Exhausted Enclosures – Part 1 Overview
Part 2: Ventilation of Gas Cabinets and Exhausted Enclosures – Part 2 Gas Cabinets
An appliance or piece of equipment which consists of a top, a back and two sides providing a means of local exhaust for capturing gases, fumes, vapors and mists. Such enclosures include laboratory hoods, exhaust fume hoods and similar appliances and equipment used to retain and exhaust locally the gases, fumes, vapors and mists that could be released. Rooms or areas provided with general ventilation, in themselves, are not exhausted enclosures.
This definition hints at laboratory chemical fume hoods, which is worth discussion here. ICC ventilation requirements for exhausted enclosures are appreciably different than we use in chemical fume hood design; the IFC requires 200 feet/minute through the open face of the enclosure.
There are no statutory, prescriptive requirements for chemical fume hood ventilation; ANSI/AIHA Z9.5, Laboratory Ventilation, 2012 is an excellent reference document. This standard recommends a range of 80-100 feet/minute for ventilation. Also, ASHRAE 110 is a test procedure which the designer can consult when contemplating a chemical fume hood installation.
These different ventilation rates are not perfectly coherent in the codes, though our experience is no code official or authority having jurisdiction has ever expected chemical fume hoods to comply with the exhausted enclosure rates.
In gas distribution we frequently deploy valve manifold boxes (VMBs) to allow safe distribution and isolation of multiple gas demands. VMBs are not specifically covered in the ICC family, however the International Fire Code discusses “ventilated enclosure” in the semiconductor chapter, always next to exhausted enclosures. One can argue a VMB is not an exhausted enclosure, as it does not meet the geometric definition. At Hallam-ICS we consider VMBs as exhausted enclosures, to be conservative and offer a likely simpler permitting path with code officials (or authorities having jurisdiction).
*CGA G-13
The Compressed Gas Association publishes this document, “Storage and Handling of Silane and Silane Mixtures” which covers all aspects of silane system design. This blog post covers gas cabinets and exhausted enclosures and describes valve manifold boxes (VMBs). The ICC and NFPA codes more generally describe VMBs as exhausted enclosures.
Ventilation rate selection is an important part of the deployment and use of gas cabinets and exhausted enclosures. The ventilation provides a measure of safety and deserves thoughtful attention by the design team. The time between initial rate selection and testing can be years, memorialize the important elements of your design work so the owner, supplier, installer, test agency, and code official understand the design requirements.
About the Author
Bill has been a mechanical engineer since 1995 and with Hallam-ICS since 2010. His career has brought him to the top of the Transamerica Pyramid Center, chemical plants, underground mines, paper mills, and semiconductor fabrication facilities. He has experience designing, specifying and installing mechanical and electrical systems in the built environment covering industrial, institutional and commercial facilities.
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About Hallam-ICS
Hallam-ICS is an engineering and automation company that designs MEP systems for facilities and plants, engineers control and automation solutions, and ensures safety and regulatory compliance through arc flash studies, commissioning, and validation. Our offices are located in Massachusetts, Connecticut, New York, Vermont and North Carolina and our projects take us world-wide.