Several laboratories are equipped with snorkel ducts, which consist of a bell mouth and an articulated connection to the exhaust system (Figure 17.5). The main difference between your laboratory chemical hood and the snorkel is that the latter does not fully surround the reaction at the point of release. For this reason, snorkels are not a substitute for a laboratory hood when handling toxic chemicals. Snorkels are far less effective in capturing dusts, mists, or fumes, and can typically only capture contaminants released within 6 inches (15 cm) of the unit. Snorkels are extremely susceptible to cross drafts.
A good use for laboratory snorkels is the capture and removal of thermal updrafts from benchtop-heated processes, or as local ventilation for benchtop apparatuses such as gas chromatographs. Snorkels generally operate at 45 feet per minute (fpm).