NEWSLETTER
ISSUE
Jan to Mar, 2022 Volume 17
BRAIN WAVE
Pure Steam Validation
What is Pure Steam
Steam which is Pyrogen free, saturated, dry, and on condensation meets all the criteria of WFI (Water for Injection) is defined as PureSteam2. Pure Steam is water that has been heated above 100 degrees Celsius and vaporized in manner that prevents source water entrainment.It is produced from purified water as per USP guidelines.
Characteristic of Pure Steam (As per EN 285, HTM 2010 & USP 40)
- Conductivity: 1.3 µS/cm (250C)
- Non-Condensable gases: < 3.5 % V/V
- Moisture: < 5%
- Superheat: < 250C
- Bacterial endotoxins: < 0.25 EU/ml
- pH: 5-7
- TOC: < 500 ppb
- Bacteria: 10 CFU/100ml
Why Pure Steam Validation is important
- Non-Condensable gases
- Dryness fraction
- Degree of Super heat
Why do we check these parameters?
Non-Condensable gases(NCG):
NCG mainly consists of gases such as Nitrogen, Carbon dioxide, Ammonia, oxygen, and halogenated hydrocarbons. As per EN 285, ‘’the Non-Condensable gases test is used to demonstrate that the level of non-condensable gases contained in the steam will not prevent the attainment of sterilization conditions in any part of the sterilizer load.’’ NCG affects sterilization process, energy efficiency and life of equipment. In sterilization, NCG can insulate the load to be sterilized, which could inhibit heat penetration to the surface of the object thereby resulting in improper sterilization.
In addition, Non-Condensable gases reduces the heat transfer efficiency of the Pure steam generators. If not removed, it forms a stagnant film on the wall of heat transfer surfaces and adds resistance to heat transfer. To overcome this issue, NCGR (Non-Condensable Gas Removal System) is used.
The concentration of Non-Condensable Gases in Pure Steam should be less than 3.5%
Dryness Fraction :
The Dryness fraction denotes the mass of gas in the mass of saturated steam, in other words it indicates the moisture present within the steam. A Dryness fraction value of 0 indicates 100% water and 1 indicates dry saturated steam having no water. So, the steam with dryness fraction of 0.9 will be combination of 10% water and 90% saturated steam.
In the process of sterilization, at the end of the cycle, the load should be sufficiently dry. As per EN 285, ‘’the mass of the load shall not increase by more than 1% for textile and 0.2% for metal load after sterilization cycle’’. Wet load at the end of the sterilization cycle results in being a breeding ground for bacteria. Therefore, it is of utmost importance that the load remains dry.
The heating process in a sterilizer eventually results in condensation of the steam, releasing the latent heat. The latent heat of the steam is directly linked with the dryness fraction. Steam with 50% latent heat, at its saturation pressure, will have dryness fraction of 0.5. So, when the steam has full latent heat, it will be dry and saturated with dryness fraction of 1.
As the heating process in sterilization inevitably generates condensation, it is wrongly assumed that the variation in pure steam dryness fraction, is of least importance. Consider an example where this condensate is retained on the load. During drying phase of the sterilization cycle, a vacuum is created, which reduces the boiling point of condensate (water). With reduced boiling point, the condensate will have excess sensible heat. This excess sensible heat is sufficient to vaporize only the small portion of the condensate. Balance energy required to evaporate the remaining condensate is compensated by the load in the sterilizer. The energy used to heat the load is partially utilized to evaporate the condensate. Therefore, a lower dryness fraction resulting in higher condensation will require more energy and time to dry the load.
“As per EN 285” the dryness value of steam should > 0.95.
Degree of Super heat:
As per EN 285, “the degree of superheat is used to demonstrate that the steam supply system is adequate to prevent the steam from being superheated at the connection point.’’
Saturated Steam at an elevated temperature is called Superheated steam. Superheated steam generation is a unique process. Once the dry saturated steam is generated in the conventional pure steam generator, its pressure is reduced with pressure reducing valve or orifice. This reduction, changes the pure steam pressure keeping the heat energy unchanged. As a result, the steam has excess energy. This excess energy increases the temperature of the steam, making it superheated.
Following table will illustrate effect of pressure drop on dryness fraction.
| Pressure – Dryness fraction (before pressure drop) | Pressure – Dryness fraction (after pressure drop) |
|---|---|
| 5 BarA – 0.95 | 3.2 BarA – 0.96 |
| 5 BarA – 0.98 | 3.2 BarA – 0.99 |
| 5 BarA – 0.95 | 2.1 BarA – 0.97 |
| 5 BarA – 0.98 | 2.1 BarA – 1.0 |
High degree of superheat in steam is undesirable for the process of sterilization. Superheated steam acts as hot air until the steam temperature is reduced to the saturation temperature. This excess temperature can damage the load and packaging. The extent of damage will depend on the rate at which the superheat temperature will reduce. The reduction rate in turn is dependent on the nature of load. i.e. the load with low heat capacity will take longer time. So, the impact of superheated steam will be higher on such load. Higher impact is also observed with small batch quantity and short sterilization cycle. In a hospital, a shorter cycle of 1340C for 3 minutes is used. Therefore, the impact of superheated steam is much higher than in Pharmaceutical industry.
The steam when expanded to atmospheric pressure the degree of superheat measured shall not exceed 250C.
Why Pharmalab
As mentioned above, Steam is an important and critical part of any sterile manufacturing. Maintaining the quality of the steam and validating it periodically is critical. The absence of steam quality as per EN 285 will affect the manufacturing process like failed sterilization, damage to load or packaging, improper SIP, wet pack issues, air humidification and so on.
To perform the test accurately, detailed understanding of the subject and experience of performing the test is essential. In today’s busy world it becomes challenging to perform an accurate test at regular interval consistently. Being manufacturer and market leader of Pure Steam Generation and WFI generation system, Pure steam is Pharmalab’ s core competence. Our trained professionals perform steam quality validation regularly which has helped us in developing an expertise in pure steam validation. With aim of helping our customers maintaining the steam quality, Pharmalab offers comprehensive solution with Trial, Validation, Training & Documentation.
Contact us for any support related to Pure Steam on mkt@pharmalab.com
Source:
- EN 285: 2015
- ASME BPE
- The Application of Steam Quality Test Limit, by Keith Shuttleworth
