When properly used, autoclaves are an important part of any tattoo shop's overall sanitation program to keep both customers and artists safe from potential infections. An autoclave is a pressurized device designed to heat aqueous solutions above their boiling point to achieve sterilization. It was invented by Charles Chamberland in 1879. The term autoclave is also used to describe an industrial machine in which elevated temperature and pressure are used in processing materials.
Under ordinary circumstances (at standard pressure), liquid water cannot be heated above approximately 100 °C (99.99 °C at 101.325 kPa, 99.62 °C at 100 kPa) in an open vessel except for special situations. Further heating results in boiling, but does not raise the temperature of the liquid water. However, when water is heated in a sealed vessel such as an autoclave, it is possible to heat liquid water to a much higher temperature. As the container is heated the pressure rises due to the constant volume of the container (see the ideal gas law). The boiling point of the water is raised because the amount of energy needed to form steam against the higher pressure is increased.
An autoclave used for sterilising tattoo equipment
Air removalWhen the goal of autoclaving is to achieve sterility, it is very important to ensure that all of the trapped air is removed. The reason for this is that hot air is very poor at achieving sterility. Steam at 134 °C can achieve in 3 minutes the same sterility that hot air at 160 °C takes two hours to achieve. Autoclaves may achieve air removal by various means including:
Downward displacement (or gravity type) - As steam enters the chamber, it fills the upper areas as it is less dense than air. This compresses the air to the bottom, forcing it out through a drain. Often a temperature sensing device is placed in the drain. Only when air evacuation is complete should discharge stop. Flow is usually controlled through the use of a steam trap or a solenoid valve, but bleed holes are sometimes used, often in conjunction with a solenoid valve. As the steam and air mix it is also possible to force out the mixture from locations in the chamber other than the bottom.
Another kind of autoclave for sterilising tattoo equipment
- Some autoclaves remove air by using a series of steam pulses, in which the chamber is alternately pressurised and then depressurised to near atmospheric pressure.
Vacuum pumps - Some autoclaves use vacuum pumps to suck air or air/steam mixtures from the chamber.
Superatmospheric - This type of cycle uses a vacuum pump. It starts with a vacuum followed by a steam pulse and then a vacuum followed by a steam pulse. The number of pulses depends on the particular autoclave and cycle chosen.
Subatmospheric - Similar to superatmospheric cycles, but chamber pressure never exceeds atmospheric until they pressurize up to the sterilizing temperature.
Autoclaves are widely used in microbiology, medicine, sterilising instruments for body piercing and tattooing, veterinary science, dentistry, podiatry and metallurgy.
Uses of Autoclaves
Autoclaves in medicineA medical autoclave is a device that uses steam to sterilize equipment and other objects. This means that all bacteria, viruses, fungi, and spores are inactivated. However, prions, like those associated with Creutzfeldt-Jakob disease, also may not be destroyed by autoclaving at the typical 121 degrees Celsius for 15 minutes or 134 degrees Celsius for 3 minutes, but can be destroyed with a longer sterilisation cycle of 134 degrees Celsius for 18 minutes.
Autoclaves are found in many medical settings and other places that need to ensure sterility of an object. Many procedures today use single-use items rather than sterilized, reusable items. This first happened with hypodermic needles, but today many surgical instruments (such as forceps, needle holders, and scalpel handles) are commonly single-use items rather than reusable.
Because damp heat is used, heat-labile products (such as some plastics) cannot be sterilised this way or they will melt. Some paper or other products that may be damaged by the steam must also be sterilized another way. In all autoclaves, items should always be separated to allow the steam to penetrate the load evenly.
Autoclaving is often used to sterilize medical waste prior to disposal in the standard municipal solid waste stream. This application has grown as an alternative to incineration due to environmental and health concerns raised by combustion byproducts from incinerators, especially from the small units which were commonly operated at individual hospitals. Incineration or a similar thermal oxidation process is still generally mandated for pathological waste and other very toxic and/or infectious medical wastes.
Unlike the humid environment produced by conventional steam, the unsaturated chemical vapor method is a low-humidity process. No time-consuming drying phase is needed, because nothing gets wet. The heat-up time is shorter than for most steam sterilizers, and the heaters stay on between cycles to minimize warm-up time and increase the instrument turnover.
Steam autoclaves, however, are really the only kind acceptable in the tattoo field. There are different styles of steam autoclaves, all acceptable to use in the sterilization of the equipment. It is a good idea to ask to see the autoclave. Is it clean? More importantly, was the shop personnel more than happy to show it to you, or did they act like they had something to hide?
Also, keep in mind that the presence of an autoclave does not mean effective sterilization. Autoclaves need to be regularly tested to ensure that they are working properly. Ask to see the results of their latest spore test. These results should be no more than two months old.
Some non-professional artists will try to convince you that a pressure cooker designed for canning food is acceptable for sterilizing used tattoo equipment. This is not true. Kitchen pressure cookers do not reach the temperature or pressure required to effectively kill all blood borne pathogens. Do not trust anyone using a kitchen unit. Medical sterilizers are much larger and are designed specifically for killing bacteria and other pathogens.