What are disadvantages of gas sterilization?

Ethylene oxide and formaldehyde are two commonly used gases for sterilisation purposes

Advantages of ethylene oxide gas sterilisation

- Ethylene oxide is a gas at room temperature (boiling point 10.7°C)

- Readily permeates plastics, cardboards, cloth

- Gases are extremely effective at killing microorganisms

- The bacterial spores are only about 5 times more resistant than vegetative cells (unlike the other sterilisation methods)

- The reactive hydrogen atoms can all be replaced by hydroxyl-ethyl groups, and this replacement will interfere with a wide variety of metabolic activities

Disadvantages of ethylene oxide gas sterilisation

- Does not permeate crystals

- The levels at which it is detected exceeds safe humans for humans

- Toxicity includes burns, blistering, headache, dizziness, nausea and vomiting, weeping (lacrimation)

- Needs to be completely removed from treated products (e.g. rubber gloves) to avoid skin reactions

- Explosive mixtures are formed with air at concentrations above 3%

- Humidity may decrease activity

Advantages of formaldehyde gas sterilisation

- Formaldehyde is a gas at room temperature (boiling point - 19°C)

- Very reactive molecule, with a small difference in effectiveness between spores and cells (as is the case with ethylene oxide)

- Acts as a mutagenic agent, reacting with carbonyl, thiol, and hydroxyl groups

Disadvantages of formaldehyde gas sterilisation

- The vapour is extremely irritating to the eyes

- Weak penetrating power, and so is only really a surface bactericide

- The gas is difficult to remove and requires long airing times

- A relative humidity of ~ 75% is required in order to be effective as the gas has to dissolve in a film of moisture surrounding the bacteria