It evaporates many times faster than water. Using computer modeling techniques, it was calculated that it would take 28 minutes for our 10 litre-puddle to evaporate to dryness under the conditions described above. A 10 litre-puddle of water could take hours to evaporate. A 10 litre-spill of ethyl mercaptan, a chemical with an extremely strong odour, would evaporate in 17 minutes. Vapours represent the most insidious of hazards.
Inhalation is a direct route into the human body.
Going back to our computer model, someone standing 10 metres directly downwind from our spill would be exposed to approximately 1000 ppm of dichloromethane for the entire 28 minutes evaporation time as shown graphically below. The wind and temperature conditions are such that a fairly steady flow of dichloromethane vapour is generated. A similar graph for the toluene case shows that someone standing 10 metres downwind would be exposed to a constant level of approximately 27 ppm. The TLV-TWA for toluene is 100 ppm as well. Vapours would not represent as much of a hazard in the toluene case.