Elmac Technologies highlights ISO concerns over propagation of flames through tank PV valves

1st August 2008

With the recently introduced ISO/FDIS 28300:2008 (E) standard challenging the conventional wisdom that there is no need to fit a flame arrester to a storage tank, provided that a PV valve is installed, Elmac Technologies recommends that the gas storage industry heeds this latest piece of safety advice.

"Under the new ISO standard,” comments Elmac Technologies’ Managing Director, Dr. Martyn Cooling, “it is clearly stated that testing has demonstrated that a flame can propagate through a PV valve and into the vapour space of a tank.

"The standard also states,” he continues, “that tests have shown that ignition of a PV valve’s relief stream can result in a flashback to the pressure valve with sufficient overpressure to lift the pallet and allow the flame to enter the vapour space of the tank."

In line with API 2000 from the American National Standards Institute, the current edition of the Health & Safety Executive's HSG 176 document recommends that 'A flame arrester is not generally considered for use in conjunction with a pressure valve, because, even at low settings, the gas efflux velocity exceeds the flame speeds of most hydrocarbon gases'.

In light of the considerations outlined in ISO/FDIS 28300:2008 (E) for tanks with potentially flammable atmospheres, however, flame and explosion protection specialists, Elmac Technologies, firmly believe that tank users should err on the side of caution.

"We are in little doubt that the publication of ISO/FDIS 28300:2008 (E) will cause the API and the Health & Safety Executive to review their current recommendations," adds Dr. Cooling.

"Whilst industry has a reasonable safety record for tanks fitted with PV valves, the ISO reported test results clearly raise a question over current thinking. It, therefore, only seems appropriate to highlight this difference of opinion between the ISO, and both the API and HSG guidance. In our opinion, the most cautious approach is to follow the latest advice."

A note about ISO/FDIS 28300:2008 (E)

ISO/FDIS 28300:2008 (E) is intended for tanks containing petroleum/petroleum products, yet can also be applied to tanks containing other liquids. In such instances it is necessary to call on sound engineering practice and design.

The standard considers the causes of overpressure and vacuum; venting requirements; methods of venting, selection and installation of venting devices as well as the testing/marking of relief devices.

The standard covers the normal and emergency vapour venting requirements for above ground liquid petroleum/petroleum products storage tanks as well as above ground and under ground refrigerated storage tanks designed as atmospheric storage tanks/low pressure tanks.

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