Sterilization – Questions & Answers

What is the difference between disinfection and sterilization?
Disinfection destroys all the micro-organisms present in a given environment apart from spores: an object that has been disinfected properly may still transmit a pathogenic micro-organism. Sterilization, on the other hand, is the complete elimination of all micro-organisms including spores.

What is EN 13060?
This is the applicable European standard, relating to small steam sterilizers.

What is a Type-B autoclave?
EN 13060 distinguishes between three types of cycle:
– B cycle for sterilizing all objects (solid instruments, porous objects and A and B hollow objects, both packaged and un-packaged);
– N cycle for sterilizing only un-packaged solid instruments;
– S cycle for sterilizing un-packaged solid instruments plus one other of the types indicated for cycle B (to be specified by the maker).
Type B autoclaves are autoclaves that can carry out cycle B and thus can sterilize any kind of object.

What is the sterilization temperature band?
EN 13060 lays down that during sterilization the following nine temperatures – eight measured at different points within the load and the unoccupied space remaining in the chamber and the last
a reading taken on the saturation vapor curve according to the pressure measured in the chamber
– must be above the sterilization temperature, but not by more than 4 °C (e.g. for a cycle at 134 °C the readings must be between 134 and 138 °C, the sterilization range). In addition, there must not be more than a 2°C difference between any one reading and another at any given time. This guarantees that the conditions necessary for sterilization are kept constant and uniform throughout the period of exposure and, by means of a comparison of temperature to pressure on the saturation vapor curve, that the air has been properly removed prior to sterilization.

What are the pre-vacuum phase and any vacuum pulse phase for?
These are necessary for the removal of air from the autoclave chamber, given that at any given pressure and temperature the density of air is around 1.5 times that of steam, such that any air present during sterilization settles in the lower part of the chamber and creates so-called “air pockets”, where the temperature is not controlled and this is potentially deleterious as far as sterilization quality is concerned.

Why is drying important?
With packaged objects drying is vital to guarantee the sterility of the instruments contained in packages while in storage: the packages must be dry when removed from the autoclave at the end of the cycle, otherwise they might immediately become contaminated again.

What is the Bowie & Dick Test for?
Its purpose is to check the degree of steam penetration in the case of porous objects (e.g. gauze or fabric) and the efficiency of the air removal system. The test kit normally consists of treating a package containing a chemical process indicator according to a special sterilization cycle at 134°C for 3.5 minutes. The test is positive if the chemical indicator changes colour in line with the information given by the producer of the test kit.

What is the Vacuum or Air Leakage Test for?
This is used to test the efficacy of the air removal system and that the hydraulic system is perfectly air-tight. The test is defined according to EN 13060, which lays down that there must be a cycle that carries out this test automatically on all autoclaves that have a vacuum phase for removing air. For this test at least the vacuum phase is carried out as in the highest performing cycle offered by the machine, then the chamber is kept in isolation for a certain length of time and the increase in pressure due to any re-entry of air is checked to make sure it is lower than a pre-defined value.

What is the Helix Test for?
Its purpose is to check the degree of steam penetration in the case of hollow objects and the efficacy of the air removal system. The test uses a Teflon tube open at one end only (length 1.5 m, internal diameter 2 mm), ending with a Teflon capsule, containing a chemical process indicator. EN 13060 requires for purposes of approval the employment of this apparatus to test cycles for sterilizing hollow load A (for example B cycles). The test is positive if the chemical indicator changes colour in line with the information given by the producer.

What is the difference between type A and type B hollow loads?
According to the definition in EN 13060 type A hollow objects are instruments with an open cavity on only one side where the ratio of length to diameter of the cavity is greater than or equal to 1 and less than or equal to 750 (1 = L/D = 750) and where the length of the cavity is not greater than 1500 mm (L = 1500 mm); or, alternatively, instruments with an open cavity on both sides where the ratio of length to diameter of the cavity is greater than or equal to 2 and less than or equal to 1500 (2 = L/D = 1500) and where the length of the cavity is not greater than
3000 mm (L = 3000 mm). Type B hollow objects, on the other hand, are instruments with an open cavity on only one side where the ratio of length to diameter of the cavity is greater than or equal to 1 and less than or equal to 5 (1 = L/D = 5) and where the diameter of the cavity is greater or equal to 5 mm (D = 5 mm); or, alternatively, instruments with an open cavity on both sides where the ratio of length to diameter of the cavity is greater than or equal to 2 and less than or equal to 10 (2 = L/D = 10) and where the diameter of the cavity is greater or equal to 5 mm (D = 5 mm). The Cavity diameter (D) / Length (L) chart below shows the areas relating to type A (in blue) and type B (in orange) hollow bodies with an open cavity on only one side (for those with an open cavity on both sides, for any given cavity diameter, double the length to obtain the equivalent diagram). The space above these areas relates to those bodies where the ratio of length to diameter of the cavity is too big for them to be sterilized even with B cycles; the space below relates to bodies that are not hollow but solid.