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. 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. 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. 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. 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.