From PHARMACEUTICAL ENGINEERING, NOVEMBER/DECEMBER 2013, VOL 33, NO 6
©Copyright ISPE 2013
Steam Sterilization Principles
蒸汽灭菌原理
by Marcel Dion and Wayne Parker
This article prents how a good understanding of basic steam sterilization principles can help with avoiding most common mistakes made when using steam autoclaves.
本文论述了良好地理解基本的蒸汽灭菌原理将有助于避免蒸汽灭菌柜使用中出现的大多数常见错误。
Steam sterilization has been ud for more than a century to sterilize items that can withstand moisture and high temperature. Steam is water in the vapor state; therefore, it is non-toxic, generally readily available, and relatively easy to control. A good understanding of basic steam sterilization principles and cycles is necessary to avoid mistakes that can lead to non-sterile load items, poor performance of the equipment, personnel injury, lower productivity, higher operation and maintenance costs, and dama
bae是什么意思ge to load items. Steam sterilizers are ud for numerous applications in the pharmaceutical and medical device industries. The focus of this article is saturated steam applications, such as laboratory media sterilization, decontamination, and general component sterilization. Terminal sterilization of parenteral liquid products or devices containing liquids may require process using steam-air mixtures or super-heated water-air mixtures. The process, as well as in-situ sterilization of tanks, filters, etc., are not addresd in this article.
蒸汽灭菌用于耐热耐湿物品的灭菌已有一个多世纪。蒸汽是水的气态形式；因此，它无毒、易制取且相对易控制。良好地理解基本的蒸汽灭菌原理和周期能够避免一些错误，这些错误可能导致装载物品非无菌、设备性能低、人员伤害、产量低、运行和维护成本高，以及装载物品的破坏。蒸汽灭菌广泛应用于制药和医疗器械行业。本文的重点是饱和蒸汽的应用，如实验室培养基灭菌、净化和一般器具灭菌。注射剂产品或带液体的器械的最终灭菌可能需要使用蒸汽-空气混合气，或过热水-空气混合气。本文不涉及这些过程以及储罐、过滤器等的原位灭菌。
Steam Sterilization Principles 蒸汽灭菌原理
Six factors are particularly critical to assure successful steam sterilization:
六个确保蒸汽灭菌成功的关键因素是：
1. Time 时间
sam nickel2. Temperature 温度
3. Moisture 湿度
4. Direct steam contact 直接蒸汽接触
5. Air removal 排气
6. Drying 干燥
1. Time 时间
The exposure (sterilization) time is a critical factor simply becau all the organisms do not die at the same time. A minimum amount of time at sterilization temperature is required to kill all the organisms. Geobacillus stearothermophilus (Bst) spores are generally ud to test steam sterilizer cycles becau they are extremely resistant to moist heat sterilization. They are also non-pathogenic and commercially readily available. The number of survivors is usually plotted on a logarithmic scale. A straight line survivor curve such as the one shown in Figure 1 is typical.
暴露（灭菌）时间之所以关键，是因为不是所有的微生物都同时死去。在灭菌温度下杀死所有微
生物至少需要一定的时间。嗜热脂肪芽孢杆菌（Bst）孢子常用于测试蒸汽灭菌周期，因为其极度耐受温热灭菌，同时也不致病且容易购买。存活数量通常画成对数坐标，常见的是如图1所示的直线型存活曲线。
Figure 1. Typical survivor curve.
图1. 典型的存活曲线
The D-value (time to reduce the microbial population by 90%) for Bst should be 1.5 to 3.0 minutes at 121.1°C (250°F) .1 For the purpo of this discussion, a D121value of 2.0 minutes and a sterilization temperature of 121°C (250°F) is ud. A typical sterilization cycle will include an exposure pha of at least 20 minutes at 121°C (250°F) for a Sterility Assurance Level (SAL) of 10-4, assuming a starting population of one million (106) organisms. This means there is a one in ten thousand (10-4) chance of a single viable Bst spore surviving the process. For each additional two minutes of exposure at 121°C (250°F), the SAL is decread by a factor of ten. The required SAL varies with application. Care should be taken to assure the correct SAL is targeted prior to cycle development. The actual bioburden of the products being sterilized will logically be killed faster than Bst. The result
ant “overkill” is an accepted method for sterilization of durable items and should be ud when possible.2
121.1°C (250°F) 下Bst的D值（微生物数量减少90%所需的时间）应为1.5～3.0min。1本次讨论中采用D121值2.0min，灭菌温度121°C (250°F)。典型的灭菌周期包括至少20min 121°C (250°F)下的暴露时间，以达到10-4的无菌保证水平（SAL），假设起始微生物数量为1百万（106）。这意味着一个Bst 孢子在此过程中存活的概率为万分之一（10-4）。在121°C (250°F)下每多2min暴露时间，SAL值会下降10倍。不同应用需要不同的SAL值。周期开发时应
注意确保设定了正确的SAL值。所灭
may day
菌产品的实际生物负载逻辑上会比
Bst杀灭得快。这种所造成的“过度杀
灭”可以用于耐用物品的灭菌，而且
也应尽可能地采用。2
2. Temperature 温度
The cond critical factor in steam
sterilization is the temperature of the
saturated steam controlled in the
chamber of the sterilizer. Figure 2
clearly demonstrates how increasing the
temperature dramatically reduces the time needed to achieve sterilization. Figure 2 illustrates approximately how much time is required to achieve equivalent microbial lethality (SAL 10° with a starting population of 106, D121- value 2.0 minutes) at different moist heat exposure temperatures.3The temperature of saturated steam is directly related to the pressure at which it is controlled. The pressure- temperature relationship values are shown in saturated steam tables.4A typical cycle at 121°C (250°F) will require 15 to 17 lbs of gauge pressure (103 to 117 kPa) in the chamber of the sterilizer. The gauge pressure required will be higher than the pressure shown in the saturated steam table due to air mixed with the steam and elevation above a level. The maximum pressure in an autoclave is limited by the specifications (ASME pressure rating) of the pressure vesl (chamber and jacket).
蒸汽灭菌的第二个关键因素是灭菌柜腔室内饱和蒸汽的温度。图2说明增加温度可以显著地减少达到灭菌效果所需的时间。图2表明了在不同湿热暴露温度下达到等效细菌致死率（SAL10°，起始数量106，D121-值2.0min）大概需要的时间。3饱和蒸汽的温度与控制的压力直接相关。压力-温度关系见饱和蒸汽表。4 121°C (250°F)下典型的周期需要灭菌腔室达到15-17lbs表压（103-107kPa）。实际所需的
表压会比饱和蒸汽表中的值略高，因为蒸汽中混有
空气，且地理位置比海平面高。蒸汽灭菌柜的最大
压力由压力容器（腔室和夹套）的规格（ASME压
力等级）限制。
Figure 2. Sterilization time versus temperature.
图2. 灭菌时间与温度。
3. Moisture 湿度
Moisture in the steam has a major impact on its ability to denature, or coagulate proteins; hence the importance of using saturated steam. Saturated steam is at equilibrium with heated water at the same pressure, which means it contains the maximum amount of moisture without liquid condensate prent. Saturated steam is recommended for steam sterilization. Not all steam is acceptable for u in a sterilizer. A dedicated clean steam supply is recommended. Superheated steam, steam containing excessive liquid water, and steam containing excessive boiler additives or contaminates (such as rust) should be avoided. Superheated steam is defined as steam that is above its saturation temperature. Superheat occurs in steam distribution systems when the line pressure is dropped across a Pressure Reducing Valve (PRV). The larger the pressure drop, the more superheat is creatninja
ed. Superheated steam does not contain the required moisture necessary to assure sterilization. The excess energy in superheated steam is transient and is eventually dissipated by the items in the sterilizer chamber, but can cau difficulty when validating the sterilizer to the empty chamber temperature stabilization requirements of the European Standard EN285.5 The ideal clean steam system for steam sterilizers is regulated at 30 to 35 psig (207 to 241 kPa) at the source. EN285 indicates the steam supply pressure should not be more than twice the chamber pressure at the desired temperature. Superheat is also created when saturated steam pass over a surface at a higher temperature. The sterilizer jacket temperature should always be t slightly below the
chamber sterilization temperature to avoid
余味
superheating of the steam as it enters the
chamber.
蒸汽湿度对其蛋白灭活或变性能力影响很大，因此需要采用饱和蒸汽。饱和
蒸汽在同一压力下与加热的水达到平衡，
也就是说它含有最大量的蒸汽且不含冷
关于代沟的英语作文凝水。蒸汽灭菌推荐采用饱和蒸汽。不是
所有的蒸汽都可以用于灭菌柜，推荐采用专用的洁净蒸汽，应避免使用过热蒸汽、含液态水的蒸汽，以及含过量锅炉添加剂或污染物（如铁锈）。过热蒸汽是指饱和温度以上的蒸汽。过热发生在蒸汽分配系统中，当管路压力经减压阀（PRV）后降低的时候。压降越大，造成的过热越严重。过热蒸汽不包含确保灭菌所需的湿气。过热蒸汽的过剩能量是暂时的，最终会被灭菌腔室内的物品所消耗，但在按EN285要求验证灭菌柜空载温度稳定性时，会造成困难。用于蒸汽灭菌柜的理想洁净蒸汽系统的输出压力应控制在30-35psig（207-241kPa）。EN285指出，提供的蒸汽压力应不大于操作温度下腔室压力的2倍。过热也发生在饱和蒸汽经过高温表面时。灭菌柜夹套温度应始终稍低于腔室灭菌温度，以避免蒸汽进入腔室时过热。
4. Direct Steam Contact 直接蒸汽接触
Direct steam contact with the surface of the object to be sterilized is required for the steam to transfer its stored energy to the object. Without direct steam contact to all surfaces, the item will not be sterilized. The amount of energy stored in steam is much higher than dry air or water at the same temperature. From the saturated steam table mentioned above, one can e that it takes 419 kJ/kg (180 Btu/lb) to heat water from 0°C to 100°C (32°F to 212°F). This is the enthalpy of water (hl). It tak
es an additional 2,257 kJ/kg (970 Btu/lb) to create steam at atmospheric pressure (100°C or 212°F). This additional energy stored in the steam is the enthalpy of vaporization (he), and is the key to steam sterilization. In order for the steam to transfer its stored energy, it
must conden on the surface of the
object being sterilized.四级翻译词组
蒸汽要将潜热传给与被灭菌物品，需要与其表面发生直接蒸汽接触。没有与所有表面发生直接蒸汽接触的话，物品就不能被灭菌。蒸汽所携带的能量比同一温度下的干空气或水高出很多。从上述饱和蒸汽表可以看出，将水从0°C加热到100°C需要419 kJ/kg (180 Btu/lb)。这就是水的焓值(hl)。在大气压
力下(100°C or 212°F)，还需要2,257 kJ/kg (970 Btu/lb)的能量才能生成蒸汽。这些储存于蒸汽中的额外能量，就是气化焓(he)，也是蒸汽灭菌的关键。蒸汽为了传递其存储的能量，必须在灭菌物品的表面冷凝。
5. Air Removal 排气
Air is the biggest deterrent to steam sterilization. Air must be removed from the chamber and the load before direct steam contact and sterilization can occur. This is accomplished in a steam sterilizer by a ries of vacuum puls prior to sterilization (pre-conditioning pha). A small amount of air will always be prent in the autoclave chamber, but must be minimized. Insufficient air removal, sterilizer chamber vacuum leaks and poor steam quality (excess non-condensable gas) are the most common caus of sterilization failures.
空气是蒸汽灭菌的最大障碍。灭菌腔窒和装载物必须在直接蒸汽接触前排除空气，才能进行灭菌。在蒸汽灭菌柜中，这是通过灭菌前的一系列真空脉动操作完成的（预调节阶段）。少量空气会始终存在于蒸汽灭菌腔内，但必须尽量减少。排气不充分、灭菌腔真空泄漏及蒸汽质量差（不凝气过量）是最常见的灭菌失败因素。
6. Drying 干燥
Wrapped items must be dry before they can be aptically removed from the sterilizer. Condensation is the natural result of steam contact with the cooler surfaces of the load during the heating and exposure phas. The prence of condensation (wet packs or pouches) can cau re-contamination of the load when removed from the sterilizer. A steam sterilizer dries the load after sterilization by drawing a deep vacuum in the chamber (post- conditioning pha). A vacuum level of 1.0 to 2.0 psia (6.9 to 13.8 kPa) is recommended for efficient drying. At 1.0 psia (6.9 kPa) chamber pressure, water boils at 38.7°C (101.7°F). Therefore, the condensate will boil and be removed as steam through the sterilizer’s vacuum system. The energy required to boil the condensate comes from the load itlf. As the temperature of the load cools due to evaporation of the condensate, evaporation (drying) decreas. When the load temperature cools to the boiling point of water at the drying vacuum level, drying is negligible. Adding further drying time past this point will not provide any further drying. Optimal load drying times depend primarily on load density and packaging. Due to their low density, plastic and rubber items may require additional drying, as they cool rapidly (puld air or heated puld air drying post-conditioning process). The amount of residual moisture in a package can be determined by weighing the package before and after the sterilization process. Typically, verification of the abnce of visible water droplets on or in the package is sufficient.
包裹物品必须经过干燥后才能从灭菌柜内无菌地取出。冷凝是加热和暴露阶段中蒸汽接触物品冷表面的自然结果。从灭菌柜取出物品时，冷凝水的存在（湿包装或呼吸袋）可能引起二次污染。蒸汽灭菌通过在腔室内形成深度真空来进行灭菌后的干燥（后调节阶段）。有效干燥推荐的真空水平为1.0 - 2.0 psia (6.9 - 13.8 kPa)。腔室在在1.0 psia (6.9 kPa)下，水的沸点为38.7°C (101.7°F)。因此，冷凝水将气化，并以蒸汽形式从真空系统排出。使冷凝水气化的能量来源于物品本身。随着物品在冷凝水气化过程中降温，气化（干燥）变缓。当物品温度降到干燥真空水平对应的水沸点时，干燥速率就很慢，可忽略了。在此之后延长干燥时间意义不大。最优装载干燥时间主要取决于装载密度和包装。由于其低密度，塑料和橡胶物品可能需要额外的干燥，因为它们冷却迅速（脉动空气或加热脉动空气干燥，后调节过程）。通过对包装在灭菌前后的称重，可以计算出包装的剩于湿分量。通常来说，肉眼检查包装上或内部不存在可见水滴就足够了。
Steam Sterilization Basic Cycles
loli什么意思
蒸汽灭菌基本周期
Steam sterilization cycles typically consist of three phas:
蒸汽灭菌周期通常包含三个阶段：
1.Pre-Conditioning: during this pha, air is
removed from the chamber and the load is
humidified by means of alternating vacuum and pressure puls.
预调节：此阶段时，空气从腔室排出，通过真
空和压力脉动交替使装载加湿。
2.Exposure: during this pha, the chamber
英文字母26个字母表temperature is raid to and held at the programmed sterilizing temperature for the programmed exposure time (both are ur lectable). The exposure also may be controlled
by accumulated F0 for liquids if a load probe and
appropriate sterilizer controls are ud. Refer to point #7 in common mistakes ction below for more information on F0.
1o暴露：此阶段时，腔室温度升高至程序设定的
灭菌温度并保持设定的暴露时间（二者均可由
用户选择）。如果采用了装载探头和适当的灭菌
控制，液体的暴露也可以通过累积F0值来控制。
更多F0值的信息参照以下常见错误部分的第#7
点。
3.Post-Conditioning: during this pha, dry goods
loads are cooled and dried or a liquids load is cooled. The chamber pressure is brought to atmospheric.
后调节：此阶段时，干燥物品装
载被冷却、干燥，或者液体装载
被冷却。腔室压力回到常压。
Over the years, various cycles have
been developed for different applications. It is critical that the
proper cycles be ud.
过去几年间，针对不同的应用开
发出了不同的周期。采用适当的周期
也很关键。
• A basic gravity cycle (cycle without pre-vacuum) can be ud for items such as unwrapped metal components, glassware, or non-porous items that do not entrap air.
对于那些不滞留空气的物品，如未包裹的金属器件、玻璃器皿或非多孔物，可以采用基本重力循环（无预真空循环）。
• Liquids require modified gravity cycles to prevent liquid loss from boiling over. Liquids in open or vented containers or in bottles with loo caps can be procesd in a “basic” liquid cycle (with slow exhaust). The cooling (exhaust) pha of this cycle allows for the chamber to slowly return to atmospheric pressure to prevent boil-over as en in Figure 3. Nominal liquid loss due to evaporation during the slow exhaust pha is typically 10 to 15%. The time required for the slow exhaust pha can vary considerably depending on the volume of liquid per container and per load.
Larger volumes require slower exhaust rates. U of a load probe and F0exposure control is recommended. Vented containers only are to be ud with this process.
液体物品需要采用改进的重力循环来防止沸腾溢出造成液体损失。开口或通气容器中的液体，或松盖的瓶装液体可以采用”基本”液体循环（缓慢排气）。这个循环的冷却（排气）阶段使腔室缓慢地回到常压，以防止图3所示的沸腾溢出。缓慢排气阶段的气化造成的名义液体损失通常在10-15%。根据各容器液体体积和装载不同，缓慢排气阶段的时间大不相同。更大体积需要更慢的排气速率。推荐采用装载探头和F0暴露控制。通气容器仅用于这种过程。
Figure 3. Typical liquid cycle chamber pressure at 121°C (250°F).
图3. 121°C (250°F)下典型的液体循环腔室压力
