Emergency Drains in a Floating Roof Tank

[NickVil]

Hello!
I know that in an external floating roof tank, the minimum-size primary roof drain shall be capable of preventing the roof from accumulating a water level greater than design at the maximum rainfall rate. Normally this primary drain is placed in the central point of the roof and it can be a hose.
Also, the emergency drains are installed to keep water to a lesser volume that the roofs will safely support. Such emergency drains shall not allow the product to flow onto the roof.
If we have the primary roof drain, is it necessary to install those emergency drains? I think, the function is the same.

Regards

 

[JoeTank]

They are not same thing. An emergency drain would come into play if the rainfall was extreme and to the point that the normal drains would not remove water quickly enough to prevent damage to the roof.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[IFRs]

Emergency drains are just open pipes sticking up from the ifr plate. They are essential to prevent the EFR from sinking if there is an extreme rain event or the main drain is blocked with debris or the tank valve on the end of the drain is closed, etc. They are inexpensive insurance and do not emit very much vapors.

 

[JoeTank]

Never use an emergency drain on a single deck external floating roof such as a pontoon floating roof. Product could flow onto the roof during a flooded deck condition.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[NickVil]

Thanks for your comments. Related if the deck is simple or double, would you specify the standard that mention it?
I mean, single deck roofs shall not be fitted with emergency drains. And, in addition to normal roof drains, double deck roofs shall be fitted with emergency drains, capable of discharging rainfall in excess of design directly into the product.

Regards