Question about Hazardous Area?

Question

1. What is an “explosive atmosphere?

2. Can you give me the symbol that identifies an apparatus is suitable for a hazardous area?

3. What type of Zone or Class, Division must pressurized enclosures be used in?

4. Can you explain the different types of purge and pressurization?

5. What are the specifications for Diesel engines operating in Zone 2 or Class1, Division 2?

6. Can you explain how Earth Ground Fault Receptacles operate

Answer 1

1. There is enough fuel and enough oxygen to explode if a spark were to ignite it.  

2.3.4.5.6. ???