Hydrogel will extinguish flammable apolar liquids by covering the liquid, cooling down and smothering the fire. The clay particles in the Hydrogel will block oxygen from the flammable liquid and, by its chemistry, the clay will capture the flammable liquids in between its layers. Both mechanisms will lead to a smothering of the fire.
The gel covering the liquid is very stable and re-ignition is not possible, also when gel surface is disturbed by wind or other cause, reignition of the fire will not occur. This feature, makes Hydrogel very safe to approach extinguished liquid fires.