| Fremont Industries, Inc. Technical Support Series |
(800) 436-1238 |
| Hospital Sterilizer Problems | |
| (PDF Version) | |
Section 1 – The Sterilization Process
Disease-causing bacteria can flourish in the media of air and water, especially if additional nutrients are present. These microorganisms can cause infections and maladies, and their prevention is a major concern to the hospital’s sterilization operation.
Sterilization employs heat in the destruction of microorganisms. At high temperatures the nucleic acid contained within the bacteria cells are destroyed. Bacteria die as a result of denaturation of proteins.
Since moist heat has better penetration and faster killing properties than dry heat, saturated steam is used to supply the heat source in the sterilization process. Typically, the steam to the hospital sterilizers is provided by the engineering department from the central steam generating and distribution system. The steam supply for sterilization should contain approximately 2 percent water and 98 percent dry steam. This balance is critical to maximized efficiencies.
Steam temperatures used in sterilization normally range between 270-274°F (35 psig) so the exposure and drying times to complete the process will vary depending on the type of cycle being employed (prevacuum or gravity) and the combined weight of the articles being sterilized.
The final process should result in providing the hospital with trays, instruments, and wrappers that are sterile, dry and free of deposits and corrosion.
Section 2 – Sterilizer Problems
Unfortunately, the operation of sterilizers within a hospital is not problem-free. Some of the problems commonly encountered are addressed separately below, but more often than not, the cause of the problem is a combination of various factors:
Wet Packs
Surgical instruments must be sterile. Wet materials transmit bacteria; therefore the sterility of the packs and instruments are compromised if they are wet. Wet packs typically require reprocessing which is time consuming and expensive.
Causes
- Boiler water being entrained with the steam commonly referred to as carryover.
- Improperly installed or no steam trap on steam supply line to sterilizer.
- Pack preparation and sterilizer loading techniques.
- Linen packs that are too large.
- Types and size of wrappers.
- Clogged drains and discharge lines on sterilizers.
- Leaking valves.
- Insufficient drying times.
Surgical Instrument Corrosion
This problem can cause instruments to become inoperative which results in costly replacements.
Causes
- The improper use of neutralizing amine resulting in steam condensate that has either too low or too high pH.
- Improper rinsing of laundered cloth wraps and laundering wraps with bed linens where “sour formulas” and/or quaternary ammonium fabric softeners are employed.
- Mixed metal sterilization in the same basket can cause electrolytic corrosion to take place.
- Integrity breaks in chrome-plated instruments.
- Improper rinsing of highly acidic or alkaline cleaners before sterilization.
- Saline solutions also cause corrosion problems for stainless steel.
- Incomplete deposit removal which cause under-deposit pitting to occur.
Spotting and Staining of Surgical Instruments & Wraps
Seventy-five percent of the surgical instruments available today are made of stainless steel. But the term “stainless” is frequently taken too literally. Stainless steel does have weaknesses– water spotting and staining are but two. There really is not a “stainless” type of steel. Instruments containing spots typically have to be reprocessed which is time consuming and expensive. Badly stained instruments may require replacement. Both spotting and staining do not portray sterility.
Causes
- Iron oxide corrosion products can break loose from the steam/condensate piping and enter the sterilizer with the steam which can spot the wraps.
- Rinsing instruments after washing with poor quality water can leave white mineral deposits on them.
- Rusty colored spotting on the instruments can result from instruments being rinsed with water having a high iron content or result from instrument corrosion.
- Purplish black staining can be caused by sulfides being present in paper wraps and by excessive amine chemical usage.
Black Surface Deposits on Sterilizer Internals
A fine black powder seems to form on the internal surfaces of most hospital sterilizers and instrument racks. Under this powder-like deposit, evidence of corrosion is normally absent. These black deposits have been analyzed on a number of occasions in the past and were found to consist of predominately nickel, copper and sulfur. The presence of these three deposits shows they are being formed by the reaction of nickel, iron, and copper in the monel metal with sulfides. Metallic sulfides are black.
The investigation of the black deposits on cloth wraps and sterilizer wash cloths have found high levels of sulfates present. Under the right conditions, sulfates will convert to sulfides. The same holds true for the sulfites that are commonly used as oxygen scavengers in many boiler plant water treatment programs.
These black deposits, if allowed to accumulate on the sterilizer surfaces and instrument racks, can slough off periodically and will cause black spots on the wraps and instruments.
The presence of sulfides in the sterilization process can originate from:
Causes
- Disposable, non woven wraps.
- Laundry residuals.
- Improper removal of cleaning agents.
- Boiler water carryover.
- Color change indicator tape.
Section 3 – Impurities in Steam
This problem is being addressed in this Fact Finder as a major topic for two reasons:
- As a chemical supplier and consultant to hospitals. The goal is to design a water treatment program that limit impurities in steam.
- Most problems occur in the hospital’s sterilization process regardless of their nature are almost always first blamed on a dirty plant steam. This is rarely the case unless the hospital is experiencing severe boiler water carryover problems or has not implemented a sound steam/condensate corrosion control program.
Steam Generating & Distribution System
To understand what is in the steam and why it is there, it is useful to examine the hospital steam generating and distribution system from the viewpoint of the facilities engineer, who is responsible for operating and maintaining the system.
The main requirements for hospital steam are space heat, absorption refrigeration (if used), humidification, laundry (if any), kitchen, and finally sterilizers. Steam to the sterilizers represents a very small fraction of the total steam produced, probably in the range of 3 to 5 percent. Obviously the boilers must be operated to ensure a reliable supply of steam to the entire system, and specific sterilizer steam purity requirements can be considered only after the health of the steam system is ensured.
The components of a hospital steam generating facility would typically include the following:
- Boilers - Firetube and/or Watertube
- Steam Distribution Lines
- Steam Utilization System
- Condensate Return System
- Feedwater Holding Tank, Heater, Deaerator, Etc.
- Pretreatment Equipment - Softeners, Dealkalizers, Etc
It is the goal of the facilities’ engineer to reclaim as much of the condensate steam as possible since this saves energy, water and chemicals. Most hospitals recover 70 to 85 percent of their condensate with most of the losses resulting from humidification requirements.
The boilers in most hospitals are not fitted with sophisticated steam separating devices as you will find in central utility stations where steam turbine blade deposits must be avoided so the steam quality from the hospital boilers will contain some water which is actually beneficial to the sterilization process.
Hospital Water Treatment Program
A hospital’s water treatment program should be designed to accomplish the following:
- Prevent deposits from forming on the boiler exchange surfaces.
- Prevent oxygen pitting on the boiler metals.
- Insure a steam as clean as possible for end-use.
- Reduce corrosion rates in the condensate return systems to acceptable values.
To prevent scale deposits from forming on the heat exchange surface, the following chemicals are normally utilized.
- Precipitants – Phosphates
- Chelants – EDTA
- Crystal Modifiers – Phosphonates
- Dispersants – Synthetic Polymers
Oxygen pitting corrosion is controlled by the use of:
- Chemical Oxygen Scavenger – Sulfites
Clean steam is controlled by limiting the total alkalinity and dissolved solids via continuous blowdown regulation in conjunction with:
- Antifoams – Polyglycols and Polyamides
Condensate corrosion control is obtained by the application of various volatile amines:
- Neutralizing Amines
- Morpholine
- Cyclohexylamine
- Diethylaminoethanol
- Filming Amines
- Octadecylamine
These materials are typically controlled so that the active ingredient in the steam does not exceed what is permitted by the FDA for steam that comes in direct contact with food.
Steam Impurities
One of the best ways to measure steam quality is to monitor the condensate at various locations throughout the hospital. Since steam quality to the sterilizers is often questioned, one of the monitoring sites should be from the steam supply line to the sterilizers. A cooling coil should be installed at this location so that the representative sample can be collected for analysis.
A good quality steam condensate should have values within the following control parameters:
- Total Hardness (as CaCO3) - 0 ppm
- pH - 7.8 to 8.8
- Conductivity - < 50 Mmhos
- Iron (as Fe) - < .1 ppm
- Copper (as Cu) - < .05 ppm
- Corrosion Rates - < 1 MPY (Mild Steel)
Steam filters have been installed at many hospitals where steam quality is questionable with very good success.
Conclusions
A well controlled and operated water treatment program designed to prevent the problems throughout the hospital’s entire steam should also minimize steam-related sterilizer problems. It should also be recognized that corrosion in a steam/condensate system can never be totally stopped; only controlled.
