H2S (Hydrogen sulfide) in Crude and Heavy Fuels. Hydrogen Sulfide is a colorless gas that smells like rotten eggs, it is highly poisonous. Usually the poisoning caused by H2S is through inhalation. It is found in petroleum and natural gas. At levels of 50-100 ppm (part per million), it may cause the human sense of smell to fail.Low levels of H2S can cause eye irritation, coughing and headache.At high exposures (greater than 300 ppm) H2S has the effect of causing the nose to stop perceiving its smell after a few inhalations, which may lead to the inhalation of a toxic or fatal dose. At high levels H2S gas may paralyse the lungs meaning that the victim may be unable to escape from the toxic gas without assistance. All above mentioned risks linked to H2S are well known to the oil industry but not necessarily by all personnel involved in handling and using petroleum products such as storage terminals, bunker suppliers or ship owners. In order to eliminate this risk of H2S maximum levels of H2S were set 2 ppm in liquid phase and in 50 ppm in vapor.