Pressure Relief Vents are provided in Electrolytic Capacitors to prevent explosions. In electrolytic capacitors, hydrogen gas is released during operation. Sometimes, due to reverse polarity or over voltage, the gas is released in excess. This can result in high gas pressure.
These vents rupture when the gas pressure inside the capacitor becomes excessive. When the vent ruptures, gas at high temperature is released. Hence, adequate care should be taken to protect the eyes.