Among lab ventilation standards, the American National Standards Institute’s Z9.5 is probably the most useful and comprehensive (at about 50,000 words) because it has been developed and maintained primarily by and for occupational health and safety professionals and is well-recognized by cognizant authorities. OSHA often uses ANSI Z9 standards to justify “General Duty Clause” citations, and ANSI Z9.5 is often considered the “standard of practice” in legal matters. An updated version of Z9.5 should be available this year.  SCOPE AND PURPOSE Z9.5 applies to the ventilation in most laboratories and is written for lab ventilation stakeholders with emphasis on those responsible for providing a safe laboratory, including users, operators, industrial hygienists, and safety and environmental professionals. The primary purpose of the standard is to establish minimum requirements and best practices for lab ventilation systems to protect lab personnel from physical harm and overexposure to harmful or potentially harmful airborne contaminants generated within the laboratory. The standard also addresses energy considerations where there is a potential impact on worker health and safety. 
LAYOUT AND CONTENTS In Z9.5, the word “User” (with a capital “U”) refers to the person assuming immediate and ultimate responsibility for the design, operation, or maintenance of the lab ventilation. The User could be the employer, owner, or lab director. The standard is presented in a useful two-column format with the “shalls” on the left and copious explanations plus “how and why to comply” information on the right. Appendices provide definitions, terms and units, referenced standards and publications, stack design information, an audit form for Users to determine whether compliance with the standard has been achieved, and sample contents for a lab ventilation management plan, which is also useful for complying with OSHA’s standard for occupational exposure to hazardous chemicals in laboratories.
Z9.5 includes the following sections:
  • Section 1.0, Scope, Purpose, and Applications, defines the standard’s coverage and limits.
  • Section 2.0, Laboratory Ventilation Management Program, includes requirements for general ventilation, chemical hygiene plans, a responsible person, hazard assessments, management approaches, and recordkeeping.
  • Section 3.0, Laboratory Fume Hoods, includes requirements for hood design, construction, sash use, hood types, capture and containment performance, and performance testing and monitoring. Although lab hoods are known as “laboratory fume hoods,” such hoods are not restricted to controlling fumes only. “Fume,” in this case, refers to all airborne chemical compounds.
  • Section 4.0, Other Containment Devices, includes requirements for gloveboxes, ductless hoods, and other special-purpose hoods used in labs.
  • Section 5.0, Lab Ventilation System Design, includes requirements for lab design, diversity, noise, supply air, exhaust system components, biological safety cabinets, fans, stacks, and exhaust discharge conditions.
  • Section 6.0, Commissioning and Routine Performance Tests, includes requirements for commissioning, specifications, performance testing, flow measurements, hood static pressures, and routine and special tests.
  • Section 7.0, Work Practices, includes requirements and suggestions for those who rely on lab ventilation for health and safety protection.
  • Section 8.0, Preventive Maintenance, includes requirements for inspection and maintenance.
  • Section 9.0, Air Cleaning, includes requirements for supply and exhaust air cleaning.
Lab Ventilation Standards In addition to ANSI Z9.5, the following standards and codes are applicable to laboratory ventilation:
Copies of Z9.5 are available from the AIHA Store
REQUIREMENTS While specifying many requirements for outcomes, the standard is flexible and allows the User to determine the compliance methods most suitable for the User’s facilities and equipment. The following examples of this flexible coverage identify the standard’s requirements by section number. I’ve added some thoughts on the OHS professional’s role in meeting these requirements. Section 2.3: In each operation using laboratory ventilation systems, the user shall designate a responsible person or persons.  The “responsible person” often is an OHS professional. Responsible persons may have the following duties: ensuring that existing conditions and equipment comply with applicable standards and codes, ensuring that testing and monitoring are performed on schedule, maintaining adequate records, participating in the design (new construction or renovation) of the lab ventilation system at the conception/planning stage, performing visual checks, training hood users to use the hood safely, and other tasks as needed. Section 2.4.1: [Lab ventilation systems] shall function properly and specific measures shall be taken to ensure proper and adequate performance.  The OHS professional is often charged with assessing the environment and determining which measures should be taken and what constitutes “proper and adequate performance.” The first step in an assessment is usually to identify which chemicals will or might be released during lab operations, including subsequent byproducts. After characterizing the hazard potential (largely based on physical properties, toxicity, and routes of entry), the next step is typically to ascertain, at least qualitatively, the release or emissions “picture.” At what points within a “control zone” will chemicals be emitted, and at what release rates? Will the chemical release have velocity? Has the maximum credible accidental release also been accounted for? How many employees are or could be exposed? What ventilation approaches are available for emission and exposure control? Determining answers to these questions is well within an OHS professional’s risk assessment capabilities. Section 3.3.1: The average face velocity of the hood shall be sufficient to capture and contain the hazardous chemicals for which the hood was selected … as generated under as-used conditions.  Face velocity is the velocity of air moving through the open area of a lab fume hood. Z9.5 does not specify a mandatory hood face velocity. Rather, it requires the User to define, determine, and/or measure emission capture and containment performance and then specify a hood face velocity that achieves containment goals. Section 3.3.1 suggests 80–100 feet per minute as a starting point. Face velocities as low as 60 fpm and as high as 150 fpm have been successfully used for specific lab hood operations. The OHS professional is often tasked with determining the appropriate velocities. Section 3.3.2: The flow rate of constant air volume (CAV) hoods and the minimum flow rate of variable air volume (VAV) hoods shall be sufficient to prevent hazardous concentrations of contaminants within the laboratory fume hood. In addition to maintaining proper hood face velocity, laboratory hoods shall maintain a minimum exhaust volume to ensure that contaminants are properly diluted and exhausted from a hood.  A fire or explosion could occur if the hood contains an ignition source and a gas or vapor is present at a concentration between its lower and upper flammable or explosive limits at the hood air flowrate. Before selecting a minimum airflow rate, the OHS professional should estimate the maximum credible concentration that might be reached in operations at hood locations where an ignition source may be present, then assign a minimum flow rate or other control measure capable of maintaining this concentration at 5–10 percent of the LFL or LEL.  Section 3.3.3: All hoods shall be equipped with a flow-measuring device or a face velocity alarm indicator to alert hood users to improper exhaust flow. 
The OHS professional is often charged with determining what constitutes “proper and adequate performance.”
Most OHS professionals want hood users to be able to access airflow performance data on a real-time basis, and this requirement in Z9.5 provides justification for this safeguard. Even a simple and inexpensive hood static pressure (SPh) monitor can meet this requirement.
Because SPh is simple to measure, it is not difficult to equip a hood with a permanent manometer for continuous evaluation of the hood’s performance. SPh is usually measured in the duct just downstream from the outlet collar of the hood and at the airflow required to achieve the average face velocity that the hood was designed to attain. The hood user can easily see and interpret the manometer gauge to ascertain that the airflow rate is being maintained in the hood, and it’s easy to train workers to read the manometer. (“Call the OHS Department if you see the gauge level drop below 1.0 or exceed 1.25.”) The SPh measurement approach is also valuable because it allows for a quick and easy estimate of new airflow rates if SPh values change. Here is an example using the fan laws (a set of formulas that describe ventilation) to predict a new flowrate. Assume that a conventional lab fume hood is exhausting an airflow rate of 1,150 standard cubic feet per minute of air with the hood sash at the full open position, and the hood static pressure was originally measured at 0.95 inch water gauge. Two months later the hood user reports to the OHS professional that SPh is now measuring 0.65 inch w.g. with the sash at the full open position. Assuming no changes in the hood itself, the following equation determines the reduction in airflow through the hood: Q (new) = 1,150 scfm x (0.65/0.95)0.5 = 1,150 (0.827) = 950 scfm See my Laboratory Ventilation Guidebook published and distributed by AIHA for detailed information. Section Exhaust ductwork shall be designed in accordance with current versions of ANSI/AIHA Z9.2, the ASHRAE Fundamentals Handbook, and NFPA 45.  The OHS professional can help apply referenced standards and other sources of information, such as data provided by hood manufacturers. Section 6.1.1: Performance tests shall be conducted as prescribed in the commissioning plan, laboratory ventilation management plan, or as directed by the responsible person.  Typical performance test methods include exhaust flow measurements, hood static pressure (SPh) measurements, face velocity tests, airflow visualization tests (for example, through use of smoke), auxiliary air velocity tests (when applicable), cross-drafts velocity tests, and tracer gas containment tests. The OHS professional often picks the most appropriate tests and conducts or supervises testing.
Section 6.4: Routine performance tests shall be conducted at least annually or whenever a significant change has been made to the operational characteristics of the hood system.  Testing programs are often the responsibility of the OHS department. Section 7.1: Hood users and workers shall be trained in the proper operation and use of a hood. Who better to do this than the OHS professional? Good work practices by chemists, technicians, and other hood users include placing the sash at the right height, always using the hood during open chemical operations, allowing only the appropriate chemical for the hood, avoiding rapid movements at the hood face, keeping their bodies out of the hood, keeping equipment and working materials about six inches inside the hood face, not storing chemicals in the hood, keeping the hood clean and orderly, not blocking slots and exhaust ports with equipment, checking the airflow monitor frequently to be sure the hood is working properly, and reporting irregularities to the OHS professional. Section 8.0: Inspection and maintenance shall follow a Preventive Maintenance Program developed by the User.  The OHS professional should help develop and monitor this program. Section 8.5: Records shall be maintained for all inspections and maintenance.  Often this is often done by the OHS department. Records also include ventilation system plans and specifications. Section 9.4: Air pollution control equipment shall be inspected visually at intervals no longer than one week and, if necessary, at shorter intervals.  This responsibility often falls to the OHS department. As you can see, an OHS professional should be (and often is) involved in applying, interpreting, and managing many of the important provisions of the Z9.5 standard. An update of ANSI Z9.5 is expected later this year. Users of the standard should ensure that they have the most recent version.    D. JEFF BURTON, MS, PE, CIH (VS 2012), CSP (VS 2002), is an industrial hygiene engineer with broad experience in ventilation used for emission and exposure control. He can be reached via email. Send feedback to The Synergist.
RESOURCE AIHA: Laboratory Ventilation Guidebook, 2nd edition (2017).
Applying the ANSI Z9.5 Standard on Laboratory Ventilation
FLEXIBLE and User Friendly 
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My apologies for the error.
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Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers