Tank Types

• Coned Roof

• Internal/Covered Floaters

• External/Open Top Floaters

Cone Roof Tanks

Cone Roof Tanks

Normally contain high flash-point liquids

Cone Roof Tanks

Cone roof tanks have a vapor space between the liquid level and the roof.

Cone Roof Tanks

At the time of ignition if the vapor space between the liquid surface is in the flammable range, a vapor air explosion will occur.

Cone Roof Tanks

Cone roof tanks are equipped with a pressure/vacuum relief device to adjust the internal pressure so that it is nearly equal to the external atmospheric pressure

Pressure/Vacuum Vent

Pressure/Vacuum Vent

As liquid enters the internal space, the pressure created by the compressing vapor is vented to the atmosphere or directed to a vapor recovery system.

Pressure/Vacuum Vent

When the product in the tank is discharged, the pressure/vacuum vent allows air to enter the tank, preventing damage that may be caused by the negative pressure.

Pressure/Vacuum Vent

Roof To Shell Seam

The roof to shell weld on cone roof tanks are only welded on one side.

Roof To Shell Seam

This weak seam provides a point of failure during the case of a vapor air explosion. It prevents tank failure at the base of the tank.

Roof To Shell Seam

Weak Seam

Roof To Shell Seam

Incidents Involving Coned Roof Tanks

• Pressure/Vacuum vent fires

• Fish mouthed fires

• Full surface fires

• Manifold fires

• Dike fires

Open Top Floaters

Open Top Floaters

Open Top Floaters

The floating roof eliminates the vapor space above the liquid.

Open Top Floaters

Open top, or external floaters, are designed with a stiffening ring (commonly known as a wind girder) to add support due to the absence of a roof.

Wind Girder

Roof Seals

• Provide spacing to allow for the roof to travel up and down on the product without touching the tank wall.

• Provide a barrier between the fuel surface and the atmosphere.

Roof Seals

Roof Seals

Incidents Involving Open Top Floaters

• Seal fires

• Full surface fires

• Dike fires

• Manifold fires

Internal Floating Roof Tanks

Same basic design as the open top floater but it also utilizes a fixed roof.

Internal Floating Roof Tanks

Internal Floating Roof Tanks

Internal Floating Roof Tanks

Internal floating roof tanks can be identified and distinguished from the cone roof tank and

the open top floater by the characteristic “eyebrow” vents at the top of the tank shell.

Internal Floating Roof Tanks

Eyebrow Vent

Incidents Involving Internal Floaters

• Vent fires

• Fish mouthed fires

• Full surface fires

• Dike fires

• Manifold fires

Causes Of Ignition

• Lightening strikes

• Hot work on live tanks

• Flare stack fall-out

• Over heat or failure of mixers

• Over-fill with remote ignition sources

• Floating roof contact with tank shell

Reducing The Risk Of Ignition• Secondary seals for high vapor

pressure products.

• Fire retardant rimseal materials.

• Independent high level alarms.

• Linear heat detection in the rimseal.

• Wind girders with handrails, to facilitate inspection of seal areas, and foam application to the seal area.

• System maintenance

Costs Associated With Tank Fires

• Denver International Airport Tank Farm, USA. Fuel pump failure. - 32,000,000

• Marine Terminal, Naples Italy.

Tank overfill. - $42,000,000

• Refinery Tank Farm, Milford Haven, U.K. Exposed oil on the roof. - $11,100,000

• Tank Farm, Newark, N.J. USA,

Overfill - $ 35,000,000

• Tank Farm, Romeoville, Illinois, USA

Lightning strike. - $8,000,000