Health and Safety

A popular product of non-bleach disinfectants used for cleanrooms and biosafety cabinets is the class of liquid sporicidal disinfectants. Since their introduction, liquid sporicides have become one of the products of choice for many biological research and production facilities wherever high-level microbial control is critical. These sporicides are in the class of liquid, cold, fast-acting disinfectants/sterilants primarily used on hard, pre-cleaned surfaces. They provide quick and effective microbial control including the ability to destroy bacterial spores. They are generally regarded as safe to use on stainless steel, glass, plastics, walls, and floors. Most sporicides are available as a ready to use pre-mixed solution or a concentrate and can be applied by immersion, spraying, fogging, or wiping. Although marketed as a low toxicity product, appropriate care during use is essential to prevent potentially dangerous conditions, exposures, and injuries.

The popular liquid sporicides are a stabilized blend of hydrogen peroxide and acetic acid. As a cold chemical disinfectant/sterilant, they are one of the fastest acting microbial controls available. Most sporicides will disinfect in around ten minutes and kill spores within eleven hours according to product literature.¹ Concentrates, which contain up to 22% hydrogen peroxide and 4.5% peroxyacetic acid, are meant to be diluted, usually 100 times (one part sporicide to 99 parts purified water) for the working solution. Surfaces are left wet for up to eleven hours, and devices soaked for the same time, to provide sterilization with spore inactivation. For germicidal disinfection or use as a cleaner/sanitizer, the working solution requires a ten minute contact and is either sprayed on and allowed to air dry or wiped on with a cloth or sponge then rinsed with purified water and air dried. Working solutions for disinfection and sanitization can be stored for up to seven days.

The pre-mixed solutions usually contain less than 10% acetic acid with small amounts of hydrogen peroxide and peracetic acid. Pre-mixed or ready to use sporicide solutions require similar contact or immersion times for sterilization and/or disinfection ranging from 5.5 hours to as little as 30 seconds for use as a germicidal disinfectant spray. Whether you use the concentrate or the pre-mixed solutions, the sterility assurance level (SAL) for the widely used sporicides are at least 10-⁶ meaning there is only a one in a million chance that a live microbe survived contact— demonstrating the products’ lethal effectiveness.² However, these liquid sporicides are not without latent drawbacks. Hydrogen peroxide is very reactive and, if it is inadvertently mixed with bleach, release of hydrogen gas occurs—which is highly flammable and potentially explosive. Liquid sporicide use requires rigorous attention to ventilation and proper employee PPE.

Can using a liquid sporicide be dangerous? (Recognizing the hazards)
Hydrogen peroxide is a colorless liquid with a bitter taste at room temperature. Its molecular weight is 34, thus it is heavier than air meaning that vapors will settle if not exhausted properly. Although it has a high boiling point of 152° C (306° F) the vapor pressure is very low (5mm Hg) so it readily evaporates. Even though hydrogen peroxide is not combustible it is a powerful oxidizer creating many opportunities for contact with incompatible materials that could result in violent explosions, spontaneous ignitions, and combustion. Avoid contact between hydrogen peroxide and combustible materials such as wood, paper and oils, organic materials like alcohol, acetone and aldehydes, metals, metal salts, and strong mineral acids, all of which could lead to violent reactions or explosions.

Due to its reactivity, hydrogen peroxide presents a serious health hazard. It is a potent irritant to the eyes, skin, and mucous membranes. Inhalation of vapors or mists may cause extreme irritation of the upper airways, i.e. nose and throat. Signs and symptoms of exposure range from stinging and tearing of the eyes, to mild bronchitis to pulmonary edema. Skin contact can produce redness and blisters and bleaching or whitening of the hair and skin. Exposure to concentrations as low as 7ppm can cause lung irritation and the OSHA occupational permissible exposure limit is only 1 ppm for a regular eight hour work shift. Concentrations above 75ppm are immediately dangerous to life and health (IDLH).³

Acetic acid, the other active ingredient of popular liquid sporicides, is very similar to hydrogen peroxide in terms of physical properties and exposure symptoms. It is primarily a reactive in concentrations relative to sporicidal use. Most people probably think of vinegar when acetic acid is mentioned. Acetic acid, a colorless liquid with a vinegar odor, has a molecular weight much heavier than air (60), high boiling point 118° C (244° F) and low vapor pressure (11mm Hg). It is also irritating to skin, eyes and mucous membranes and induces the same exposure symptoms as hydrogen peroxide except skin will turn black instead of bleaching out. The OSHA permissible exposure limit is 10ppm with the IDLH limit at 50ppm.