Rain Flare / Flare Liquid Carry Over Incident

Created on September 12, 2022

Rain Flare is a phenomena where hydrocarbon liquid was carried over to flare stack due to failure of high level monitoring or high-high level safety instrumented system during emergency relief condition. It causes burning liquid coming out from flare tip to the nearby surroundings. This incident can proves catastrophic causing fatality, major asset damage, and various environmental issues in various cases.

API STD 521 Pressure-relieving and Depressuring Systems highlights this risk specifically in section as follows

Risk of Overfilling Flare Knockout Drum

The risk of overfilling the flare knockout drum shall be assessed. Most flares are not designed to effectively combust
liquid. These evaluations should consider the effect of the following:

a) the amount of liquid in the knockout drum prior to the release including the removal time;
b) mitigation or prevention of liquid overfill by means of level monitoring
c) the liquid weight on flare header and flare stack mechanical integrity;
d) the discharge of liquid from the flare (i.e. potential for flame-out, excessive smoke and unburned hydrocarbon emissions, discharge of “burning rain,” pool fires around the flare stack, etc.);
e) the flare siting/location in proximity to areas where people can be exposed, property fence-lines, units, etc

Some technical advises related risk in flare system also can be seen at ICHEME paper here :


Do you have any experiences related to Flare Liquid Carry Over in your working place ? Feel free to share in the comment below

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