Area Classification: AP RP 500 Appendix D Figure D4

[D!NNy]

Information of my project

1. Gases that are present in my area are lighter than air.
2. Pressure of the gases in my project range from 450 to 930 PSIG, to define the area class radius two important things to know is the pressure and operating temperature of gas
a. Using figure D-1 in API 500 Appendix D we are category 1, this is purely based on the pressure. At the given pressure above, operating temperature doesn’t matter anymore.
b. Using figure D-2 in API 500 Appendix D based on the mass release rate we can determine the HAC radius, but this is for materials that are heavier than air
i. Low (<10 gal/min) = 25ft radii
ii. Medium (10-50 gal/min) = 50ft radii
iii. High (50-100 gal/min) = 100ft radii
3. Determining the hazard radius for sources handling lighter than air gases and vapor: For point source HAC radii it refers to figure D4.

However i am having hard time understand this can someone explain how to use this figure to define HAC Radii??

Thanks for the help in advance.

 

[D!NNy]

here is the closer view of the figure.
Thanks

 

[rbalex]

Electrical classification isn't rocket science but it is largely based on experience. For example see RP 500 Section 7.2.3:

... Thus, dimensional limits recommended for Division 1 or Division 2 locations are based on experience, as well as theoretical diffusion of gases or vapors of the types prevalent in petroleum operations. ...

There are similar statements elsewhere in RP 500 and in NFPA 497 as well.

I suggest reviewing Section 5.4. Read it all, it isn't too long.

Since you are talking lighter than air its probably hydrogen or methane. At the pressures you're talking about hydrogen is virtually self-igniting from air friction and you may as well consider a 30' Hazard Radius for methane.