Guide to the safe handling of solvents in a bituminous ... - Aapaq.org

• replace air as it is exhausted to the outside via local ventilationdevices such as fume hoods;• provide a controlled environment for specialised areas such assurgery or computer rooms.General ventilation systems comprise an air supply and an air exhaust.The air may be supplied via a central HVAC (Heating, Ventilation and AirConditioning) system or, especially in older buildings, via opening windows.Laboratory air may be exhausted through either local exhaust devices or airreturns connected to the HVAC system. Local exhaust ventilation systemscapture and discharge air contaminants or heat from points of release.Common local exhaust ventilation devices found in laboratories include:• chemical fume hoods;• canopy hoods;• slotted hoods;• biological safety cabinets;• direct connections.Chemical hoods, canopy hoods and direct connections exhaust devicescan be used for binder and asphalt laboratories:• Chemical fume hoods: Chemical fume hoods are enclosed unitswith a sliding sash for opening or closing the hood. They are able tocapture and exhaust even heavy vapours, and are preferred for alllaboratory procedures that require manual handling of hazardouschemical material. (Refer to sub-section on safe use of chemical fumehoods below for information on the safe use of chemical fume hoods).• Canopy hoods: Canopy hoods are designed to capture heat fromprocesses or equipment, such as atomic absorptionspectrophotometers or autoclaves; a canopy or bonnet is suspendedover a process and connected to an exhaust vent. The followinglimitations make canopy hoods poor substitutes for chemical fumehoods, because they: draw contaminated air through the user’s breathing zone; do not capture heavy vapours; provide less containment than chemical fume hoods, and aremore affected by air turbulence; do not provide adequate suction more than a few inches awayfrom the hood opening.58