It is the first responsibility and discretion of the scientific investigator to establish a protective layer between him or herself and chemical hazards using the appropriate personal protective equipment (PPE). However, the laboratory fume hood provides a more robust and quantitative safety, mechanical, and atmospheric barrier against toxic vapors, powders, and spills. There are also elements of hood design and construction specifically tailored to different chemical workflows that vary in purpose and scale.
Investigators and lab managers should plan on upgrading or replacing hood systems when it becomes clear that they will have to accommodate laboratory space or personnel changes in Laboratory Fume Hood Manufacturer in India . Hood system replacements and overhauls are especially requisite when the nature of overall application shifts to a new type and degree of chemical workflow.
The work cabinet and surface
Primarily, a fume hood is somewhat of an elevated box, albeit with some caveats. Perhaps the most important caveat is that when the sash is raised (or widened), the work cabinet must be able to maintain a safe perpendicular air speed, or face velocity, at the imaginary plane that marks the interface between worker and working surface. Face velocity correlates to the volumetric flow of air that must be employed inside the hood to contain vapors before they are ducted and exhausted. Although face velocities at 50 percent sash height often exceed 100 fpm, some contemporary high-performance cabinets can now safely run with face velocities as low as 40 fpm, translating to great energy and cost savings by minimizing volumetric flow.
In addition to improvements in airflow, performance, and environmental impact, work cabinet surfaces have evolved to meet and exceed rigorous measures against corrosion and degradation, and to enable clean-up or wash-down. Standard cabinet surfaces are often composed of seamless fiberglass construction to guard against the collection of powders and entry of corrosive vapors into hard-to-clean crevices. Additionally, mobile inserts molded of composite or epoxy resin can aid containment and clean-up.
Modifications for different chemical workflows
Specific chemical workflows have propelled design changes in cabinet size, shape, materials, and integrated equipment. The most familiar and ubiquitous designs are the general purpose standing or benchtop ducted hood, which exhausts vapors outside through building HVAC; and the portable filtered hood, with efficient molecular filters that release clean air back into the laboratory. There are several other specialized types, however, each with their own associated materials and components.
Safety monitoring
How do you know whether the working face velocity is adequate to sequester vapors away from you? The first line of defense is to strictly adhere to regular re-certification paradigms scheduled through chemical safety officers. This will ensure that the hood performs to its standards, and extend its longevity.
Blowers and ducting
Similar to the face velocity at the plane of the sash, a safe hood must maintain a threshold duct velocity to adequately move vapors out of the hood and propel them through building systems to the outside. This necessitates a symbiosis between hood capacity, blower size, and ducting layout to optimize the airflow appropriate for the size and type of hood. A weak blower exhausting a large cabinet will not sufficiently expel vapors, while a powerful blower can potentially overwhelm the duct system and create turbulence within the cabinet airflow, compromising both face and duct velocities.
In all possible iterations of fume hoods and associated componentry, the litany of codes and standards that independently govern each part can be overwhelming. However, as Fulmer explains, the ANSI Z9.5 Standard for Laboratory Ventilation, which is comprehensive, is however “superseded by any local building codes.” Depending on the needs of the investigator, and the capacity of the building, the appropriate fume hood option is always available.
