Exp Systems

Question 1

What is EXp?

Answer 1

Protective gas is supplied to an enclosure in order to prevent the formation of an explosive atmosphere inside the enclosure

Question 2

What are the characteristics of protective gas?

5

Answer 2

Two sources may be required depending on risk
Non-toxic and free from foreign bodies
Not normally contain more oxygen by volume than air
source should be taken from a non-hazardous area
temperature should not exceed 40 deg

Question 3

What are the three methods of pressurisation?

Answer 3

Static
Pressurisation with leakage compensation
Pressurisation with continuous flow

Question 4

What is static pressurisation?

What is its application?

Answer 4

Apparatus is purged and pressurised outside the hazardous area
Allowed into hazardous area without a continuous supply of protective gas
Application - Transportable data collection equipment

Question 5

What is pressurisation with leakage compensation?
Why is it used?
(7)

Answer 5

• Used for when enclosure cannot be totally sealed
• Used where a source of ignition exists within enclosure
• Min overpressure should be 50 Pascals or 0.5 mbar
• Enclosure in zone 2
• No flammable material piped into enclosure
• Pressure must be maintained above outside ambient pressure
• Any leakage must be of protective gas leaving enclosure rather than flammable atmosphere inside

Question 6

What is pressurisation with continuous flow?

Answer 6

Required to maintain an internal overpressure with sufficient continuous flow of protective gas.
Done to ensure that the internal atmosphere is blew LEL in a worst case leak scenario
Used in analyser house

Question 7

What are the controls for if protective gas fails?

Answer 7

Devices should be fitted to monitor the overpressure/flow
If it falls bellow min value, an alarm should be raised
Disconnect power, dependant on zone of use

Question 8

Purging?

Answer 8

Must remove any existing flammable atmosphere

Should change the atmosphere inside the enclosure 5 times with the purge gas

Question 9

Pressurisation Rules

Answer 9

• Suitable for zone 1 and 2
• No live maintenance
• Non certified apparatus can be used inside enclosure
• Exp marking is complex, expert should be consulted
• Cable glands, non certified but suitable for cable
• Very expensive to install and maintain