There were two chemical scares in adjacent streets in Wells on Saturday.
Three cars in Southover were covered in what appeared to be a mysterious white powder at 1.30pm.
A cordon was put in place and roads closed while fire crews examined the scene.
It was determined that the substance was not harmful and most likely the powder from a discharged fire extinguisher.
Police are treating the incident as antisocial behaviour.
At around the same time fire crews were called upon to don full chemical protection suits after a resident's barometer fell off the wall and spilt toxic mercury at a home in Carlton Mews.
They consulted scientific experts who advised them to take the precautions before removing the liquid metal and contaminated articles from the property.