Approaches To Ventilation Systems
A Survey of ANSI Z9 Standards
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Various standards of practice exist to help protect workers involved in industrial operations that produce airborne contaminants. These contaminants could represent health hazards through inhalation or skin contact, create explosion and fire hazards, or lead to oxygen-deficient work environments.
The Z9 standards from the American National Standards Institute (ANSI) can help OEHS professionals cost-effectively protect employees and others from exposures to harmful airborne substances. Z9 standards generally define the minimum and regularly accepted approaches for providing safety and health-related ventilation systems. Additional controls and personal protective actions can often be used to increase the effectiveness of any standard.
This article provides a description of the currently active Z9 standards, truly some of the most important and useful LEV-related standards available to OEHS professionals. Although Z9 standards are considered “voluntary,” employers who don’t follow them risk being cited by OSHA under the General Duty Clause of the Occupational Safety and Health Act. Many Z9 standards overlap with each other, and some are intended to be used in conjunction with other Z9 standards. All Z9 standards typically contain sections that describe their scope, purpose, and proper application; relevant definitions; and references to other standards and publications. They are kept up to date through regular revision by experts in the fields they cover. The titles of these standards bear the names of the organizations that were responsible for their development.
OPEN-SURFACE TANK OPERATIONS Open-surface tanks are used in industrial processes such as electroplating, washing, dyeing, dipping, degreasing, and many others. The vapors, gases, and mists emanating from these tanks can be inhalation hazards or fire and explosion hazards. Ventilation is required to protect workers.
Often, the push-pull ventilation technique is used to control hazardous emissions from open-surface tanks. In push-pull ventilation, a jet of air is directed across an area of emission and into an exhaust hood. The jet of air carries the hazardous emission through the hood and into the ventilation system, which removes it from the work area.
Push-pull ventilation is one of the topics covered in ANSI/ASSP Z9.1-2016, Ventilation and Control of Airborne Contaminants During Open-Surface Tank Operations. The objectives of this standard are to protect open-surface tank workers by establishing minimum ventilation requirements to control emissions from open-surface tank operations; prevent explosive concentrations of gases or vapors in ducts, hoods, and enclosures; protect workers from splashes and other contact with liquids; prevent objectionable increases in humidity; and help establishments conform to local or state air pollution regulations.
In addition to push-pull ventilation, the standard discusses the classification of open-surface tank operations, requirements for controlling emissions and exposures, general exhaust ventilation, vapor degreasing tanks, and special precautions for cyanide. It also contains an appendix of chemical data and an audit form that helps OEHS professionals determine if all requirements of the standard are met.
LEV SYSTEMS LEV systems, which capture contaminants at the source before they can be dispersed into the work environment, generally have five main elements: hoods, ductwork, air cleaners, air movers (fans), and discharge stacks. LEV is commonly used during welding tasks and other workplace activities that generate harmful airborne chemical substances. The OSHA Technical Manual specifies that LEV is appropriate when: • the emission sources contain materials of relatively high hazard • the emitted materials are primarily larger-diameter particulates—that is, they are likely to settle • emissions vary over time • emission sources consist of point sources • employees work in the immediate vicinity of the emission source • the plant is located in a severe climate • minimizing air turnover is necessary
ANSI/ASSP Z9.2-2018, Fundamentals Governing the Design and Operation of Local Exhaust Ventilation Systems, is a broad, widely used standard that provides minimum requirements for the commissioning, design, specification, construction, and installation of fixed industrial LEV systems. Detailed specifications for the five main LEV system elements are included in the standard, as are guidelines for the management, operation, maintenance, and testing of LEV systems.
In general, ANSI/ASSP Z9.2 has been the most used Z9 standard because of its wide applications and its excellent information. It provides fundamental requirements to ensure satisfactory performance over the lifetime of the systems. It also describes some basic requirements for replacing air exhausted from the space being protected.
The Z9.2 standard does not specifically cover ventilation for comfort, air moving systems that are only part of an industrial process, paint booths not used for employee protection, or energy conservation. It is mainly intended to provide information and requirements for ventilation systems used for employee chemical exposure protection. For more information, visit the ANSI website.
SPRAY FINISHING Spray finishing operations involve dispersing organic or inorganic materials through automatic, manual, or electrostatic means. These operations are generally intended to coat, treat, or clean a surface. Many paint spray operations are conducted in what are known as “paint booths,” which range in size from small box-type hoods for painting small objects to large drive-in paint booths found in automobile manufacturing facilities.
ANSI/ASSP Z9.3-2017, Spray Finishing Operations: Safety Code for Design, Construction and Ventilation, is intended to help protect workers from exposures to gases, vapors, mists, dusts, powders, or solvents associated with spray finishing operations. The standard does not apply to metal spraying, dipping, spray washing, or degreasing, which are different processes than spray finishing.
Although Z9 standards are considered “voluntary,” employers who don’t follow them risk being cited under OSHA's General Duty Clause.
ABRASIVE BLASTING Abrasive blasting uses pneumatic pressure, hydraulic pressure, or centrifugal force to apply an abrasive to a surface, usually to clean or remove a coating. It can also be used to provide a texture to poured concrete. Abrasive blasting—also known as sandblasting, a term derived from the fact that sand is often the material used as the abrasive—typically generates a significant amount of dust that needs to be controlled. Not surprisingly, silica is one of the hazards commonly associated with abrasive blasting.
NIOSH cautions that unless the process is completely isolated, “abrasive blasting dusts are a very great health risk” to the operator. When used to remove lead-based paint—for example, from bridges—the particles generated by abrasive blasting pose a risk to the nervous system. Safety is also a concern: these operations are sometimes performed by workers who are positioned on scaffolds, which introduces a fall hazard, and the abrasive stream can injure nearby workers or bystanders. When used to clean the insides of industrial tanks, abrasive blasting may present a confined space risk to workers.
ANSI/ASSE Z9.4-2011 (R2021), Abrasive-Blasting Operations—Ventilation and Safe Practices for Fixed Location Enclosures, which was partly revised in 2021, applies to all operations in fixed-location abrasive-blast enclosures. It does not apply to steam blasting, steam cleaning, or hydraulic cleaning methods in which work is done without the aid of abrasives, or to abrasive blasting conducted outdoors, which typically has natural dilution of particles because of air movement and wind. Although not required by the standard, respiratory protection is often used in abrasive-blasting operations to ensure personal protection.
LABORATORY VENTILATION A variety of hazards can exist in laboratories. As noted in the OSHA publication Laboratory Safety Guidance, a comprehensive discussion of these hazards and associated controls, chemical hazards in laboratories can include carcinogens, toxins, irritants, corrosives, sensitizers, and agents that damage the lungs, skin, eyes, or mucous membranes, or that act on the blood system. Other laboratory hazards include biological and radiological hazards, physical hazards such as noise, and safety hazards such as sharps and the potential for burns.
Laboratory ventilation comes in two basic parts. The first part is associated with the HVAC system, which provides an adequate supply of fresh or clean air to replace exhausted air and displace any contaminated air in the lab and dilute it to safe levels. The second part consists of laboratory ventilation hoods, which contain, control, remove, and exhaust hazardous chemicals before they can be emitted into the laboratory air.
Every OEHS professional who works in or with a laboratory will benefit from the ventilation requirements and good practices described in ANSI/ASSP Z9.5, Laboratory Ventilation. Updated in 2022, this standard represents the most current thinking as it pertains to lab ventilation, covering performance testing, air cleaning, preventive maintenance, and work practices. Those involved in laboratory management and operation, including chemists, industrial hygienists, lab and institutional health and safety staff, and environmental health and safety staff will benefit from this excellent standard. For more information on the most recent version of this standard, read my article in the June/July 2022 issue of The Synergist.
GRINDING, POLISHING, AND BUFFING Grinding, polishing, and buffing involve the use of a tool to remove material from a workpiece or part. They often result in airborne concentrations of the materials in the breathing zones of workers. The tools usually have an abrasive wheel, which can itself contain hazardous substances that may become airborne. Many machine shops, for example, include these kinds of operations.
ANSI/ASSP Z9.6-2018, Exhaust Systems for Grinding, Polishing and Buffing, applies to instances where these tasks are completed using powered machinery but without a liquid coolant. (Where coolant is used, additional considerations are necessary to protect workers from the emission of mists, aerosols, and vapors; these considerations are not discussed in ANSI Z9.6.) The requirements and emission and exposure control principles described in this standard are intended to protect those engaged in and working in the vicinity of grinding, polishing, and buffing operations; and to control contaminants generated and emitted by these types of operations. The ACGIH Ventilation Manual has excellent examples of the kinds of exhaust hoods used for these operations.
RECIRCULATING AIR FROM INDUSTRIAL EXHAUST A growing emphasis on energy efficiency has encouraged the use of recirculated air as part of general ventilation systems. But, if done improperly, recirculating air exhausted from an industrial process can result in the reintroduction of contaminants into the work environment. Compared to conventional exhaust systems, greater attention to preventive maintenance and testing of the system is necessary when recirculating air is used.
ANSI/AIHA/ASSE Z9.7-2007, Recirculation of Air from Industrial Process Exhaust Systems, establishes the minimum criteria for the design and operation of recirculating air exhaust systems used for contaminant control in the workplace. This standard can be used to determine if the air can be passed through an air cleaning device and safely recirculated; if appropriate methods and equipment are being used to identify contaminants; and the possible health and safety problems that should be addressed. This standard is expected to be updated in the next few years. Its most recent update was in 2007.
A portable ventilation system has a hood that can be moved to the most effective control location. This can be achieved through the use of flexible ductwork attached to the hood. There are many applications of portable ventilation systems, including the collection of welding fumes; maintaining negative pressure in structures during the remediation of asbestos, lead, or mold; and controlling emissions from spray painting and abrasive blasting. These units need to be constructed to withstand poor weather and rough treatment. Due to the variety of circumstances in which these systems can be deployed, portable ventilation is a complex subject.
ANSI/ASSP Z9.9-2021, Portable Ventilation Systems, describes fundamental good practices related to the design, manufacture, labeling, application, maintenance, and testing of portable ventilation systems used for the control of airborne contaminants or environmental conditions such as those found in hand welding operations.
DILUTION VENTILATION SYSTEMS In contrast to LEV systems, which control emissions at the source before they can disperse into the environment, dilution ventilation systems often involve exhaust fans placed in the walls or roof of a building, with airbornechemicals diluted through the delivery of replacement air. Because dilution ventilation is relied upon to ventilate an entire workspace, it is sometimes a primary control of widely dispersed air pollutant sources.
ANSI/ASSE Z9.10-2017, Fundamentals Governing the Design and Operation of Dilution Ventilation Systems in Industrial Occupancies, establishes minimum dilution ventilation requirements for industrial sites where employees can be exposed to air contaminants. The standard covers requirements for the commissioning, design, specification, construction, installation, management, operation, maintenance, and testing of dilution ventilation systems used to reduce, prevent, and control employee exposures to excessive concentrations of airborne substances in the work environment. When following this standard, dilution ventilation systems generally supply and exhaust appropriate amounts of air to and from an area or a building. Also covered in Z9.10 are demand dilution ventilation systems, which continuously monitor the environment for contaminants. For more information on dilution ventilation, read my article in the December 2021 issue of The Synergist.
LABORATORY DECOMMISSIONING The decommissioning of laboratories involves preparing the site for the next occupant. Given the wide variety of materials, equipment, and processes used in laboratories, decommissioning is a complex subject and can involve the proper disposal of biological, chemical, and radioactive waste; the removal of sharps; the handling of compressed gas cylinders; and the cleaning of equipment such as refrigerators, freezers, and centrifuges. Decontamination of these items may also be necessary.
Hazardous materials used in labs are highly regulated and can present significant potential liabilities. Research labs can pose unique decommissioning concerns. The intent of ANSI/ASSE Z9.11-2016, Laboratory Decommissioning, is to provide an approach to decommissioning research laboratories that can also be applied to other types of facilities. This standard was being updated at the time this article was written.
BIOSAFETY LABORATORIES Biosafety levels, or BSLs, are designations that indicate the degree of containment necessary for operations performed within a laboratory. These designations range from BSL-1, which corresponds to the lowest level of containment, to BSL-4, the highest level. Similar designations exist for animal research laboratories (ABSL), agricultural research laboratories (BSL-Ag), and others.
ANSI/ASSP Z9.14-2020, Testing and Performance—Verification Methodologies for Biosafety Level 3 (BSL-3) and Animal Biosafety Level 3 (ABSL-3) Ventilation Systems, provides guidance for inspecting and testing the performance of BSL-3 and ABSL-3 laboratory ventilation systems used to control exposures to pathogens such as those that cause tuberculosis, botulism, and SARS-CoV-2. Animal biosafety levels are also provided for people working with vertebrate animals exposed to agents that may also infect humans.
Among the features of BSL-3 labs are self-closing, double-access doors; sealed penetrations in walls (for example, around plumbing); and containment devices such as a biosafety cabinet. Depending on the hazard, workers in BSL-3 labs may need to wear powered, air-purifying respirators. All experiments in BSL-3 labs are performed in biosafety cabinets, which may use high efficiency particulate air (HEPA) filters for both supplied and exhausted air. The exhaust air in BSL-3 labs cannot be recirculated. Potentially contaminated areas must be under negative pressure relative to clean areas to ensure that clean air is drawn into the lab. ABSL-3 labs have similar requirements.
STANDARDS DEVELOPMENT During my career as an OEHS professional I not only used Z9 standards, I participated on the subcommittees that developed several of them. This was a great experience, and I encourage others to consider volunteering. In addition to looking great on a resume, participating on a Z9 subcommittee can help you establish connections with some of the most knowledgeable ventilation professionals in the U.S.
D. JEFF BURTON, MS, PE, FAIHA (former CIH and CSP, VS), is an industrial hygiene engineer with broad experience in ventilation used for emission and exposure control. He is an adjunct faculty member at the Rocky Mountain Center for Occupational and Environmental Health at the University of Utah in Salt Lake City.
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ACGIH: Industrial Ventilation: A Manual of Recommended Practice for Design, 30th ed. (2019).
Administration for Strategic Preparedness and Response: Science Safety Security, “Biosafety Cabinets.”
Administration for Strategic Preparedness and Response: Science Safety Security, “Biosafety Level Requirements.”
American National Standards Institute: “ANSI/ASSP Z9.2-2018: Fundamentals Governing the Design and Operation of Local Exhaust Ventilation (LEV) Systems” (August 2018).
American Society of Safety Professionals: “Ventilation Systems (Z9).”
Applied Occupational and Environmental Hygiene: “An Overview of Push-Pull Ventilation Characteristics” (March 1990).
NIOSH: “Abrasive Blasting.”
OSHA: Laboratory Safety Guidance (PDF, 2011).
OSHA: “Ventilation Investigation,” Section 3, Chapter 3 of OSHA Technical Manual.
The Synergist: “Dilution Ventilation: A Requirement for Every Indoor Occupancy” (December 2021).
The Synergist: “The New Laboratory Ventilation Standard” (June/July 2022).
University of Michigan Environment, Health and Safety: “Lab Decommissioning.”