I have purchased some Submersible level sensor. Specification says, those sensors are only for safe area installation. Not for hazardous area. I want to know the definition of Hazardous area.

N.B: My application is in a tank where there are lot of sand mixed with the salty sea water. And there are also some floating sea dust. The water is not stable also. Tank size (H=12feet x L=20Feet x W=15feet.

 

A Hazardous location is an area where flammable liquids, gases or vapors or combustible dusts exist in sufficient quantities to produce an explosion or fire.

The vapor space above the liquid in a tank of gasoline is a hazardous area.

I'm not sure what sea dust is, but a tank of water is very unlikely to be a hazardous area.

 

I don't think you have an Ex atmosphere, being it is just Sea Water.
But based upon your description of sand build up and particulate you need to be aware that the submersible can get clogged. You may want to investigate a simple ultrasonic level transmitter. It would keep the sensing element out of the media . If it is a hazardous area then simply add and intrinsic barrier or maintain sealed conduit from transducer to transmitter.

 

Hazardous Area refers to the presence of combustible liquids and vapors within certain distances, distances that depend on the type and kind of ventilation in your area and the combustable fluids or vapors.

To be declared a Hazardous Area where Explosion Proof wiring and equipment are required is determined by the Electrical Department who develops an Area Classification Drawing.

Even if the dominant liquid (sea water in your case) is not flammable, the matter may depend on the likely presence of combustible materials even on an emergency basis such as due to leakage or equipment failure.

You have to rely on the owners design requirements, and install according to that.

Your responsibility is to inform you boss/manager that the device is for non-hazardous areas only.

Good luck, Safety is Important.