The OptoSniff sensor heads have been designed to operate in harsh environments such as coal mines and landfill sites. To ensure that the sensors are unaffected by the operating environments, they are rated to IP54. This rating covers dust ingress and water ingress to the following levels.
– Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment
– Splashing Water. Water splashing against the enclosure from any direction shall have no harmful effect.
Further details of IP ratings and tests can be found here