Advanced Instrument Processing Solutions

Archive for the ‘Hard Water Deposits’ Category

We have had our wash water tested and the silica level is low, yet we still have a snake skin pattern on our instruments after sterilization. Is the wash water the only source of silicates or can they be coming from somewhere else?

There are other sources of silicate deposits which I neglected to mention in my last post on them

One source is the steam in your autoclave. If water to the boiler is improperly treated, minerals that are dissolved in the water can be carried in the steam and deposit on instruments and the chamber of your autoclave.  Silica is also added to some steam boiler systems to protect the boiler and piping from corrosion, if used in excessive amounts this treatment can be deposited on instruments by the steam containing it.

Another source of silicates is in the detergents you may be using. Sodium Silicate (meta-silicate) is sometimes used in cleaning chemistry as a complexing/chelating, buffering and emulsifying agent. As a complexing agent Sodium Silicate has a great affinity for metals and will bind with dissolved metals in water, thus acting as a water softener and preventing dissolved minerals from depositing on surfaces, it is also a great wetting agent and helps keep the components of detergents in emulsion. Many laundry detergents use Sodium Silicate in their formula for this reason and because it has an affinity for metals, tends not to bind to the fibers of clothing.

Another name for dissolved sodium silicate is Water Glass or Liquid Glass and this brings us to its other use. Sodium silicate can be added to the coolant system of a car to repair gaps in the head gaskets. When sodium silicate in solution reaches a temperature of 100°-105°C (212°-221°F) it adheres to the gaps in the head gasket in the form of glass, thus sealing these gaps. The glass that is formed here can only be re-melted at 810°C (1490°F). In the U.S. governments Car Allowance Rebate System “Cash for Clunkers” program, engines of cars traded in had to be disabled so they could not be reused or resold for parts. This was done by draining the oil from the car, replacing it with 2 liters of sodium silicate solution and then running the engine. When the engine got hot enough the sodium silicate would turn glass like and abraded the engine internals causing it to seize.

Given its affinity for metal and the fact that it turns to glass at the boiling point of water, you would wonder why it would be used in any cleaning chemistry for sterile processing, yet it is, because it is a relatively inexpensive substance. It is more common to find this in cart washer chemistry than those for instruments, but here the sodium silicate takes its toll on the washer more than the carts. After repeated uses the cart washer chamber begins to exhibit a coating that one would assume is calcium, but unlike calcium deposits it is not easily remove, even wire brushes have little effect on it. Also this coating begins to build up freezing the washer arm mechanism and plugging the spray nozzles. With continued use the cart washer will become inoperable.

Sodium Silicate deposits

Sodium Silicate Deposits

We use only neutral pH enzymatic detergent in our facility. Why would we want to use an acid rinse in our washer-disinfector if we are not washing with an alkaline? Won’t the acid rinse harm our instruments?

First, I recommend you review our blog answers under the “hard water category.” That being said, it has been my experience that most institutions use tap water in their washer-disinfector, all the way up to the final thermal rinse. If the facility has the ability, they will use either de-ionized or reverse osmosis water in this final thermal rinse. Depending on where you live and the time of year, your tap water can contain a lot of dissolved minerals which can end up depositing on your instruments and in your machine’s wash chamber, eventually damaging both. An acid rinse will neutralize these minerals and keep them from forming deposits.

Now, there are certain instruments that cannot be exposed to an acid rinse (such as plated copper instruments); however, these instruments would not fare well in an alkaline wash either. Always check the manufacturer’s recommendations and instructions for cleaning.

The majority of the instruments you run through your washer are surgical grade stainless steel. These instruments have a layer of passivation that helps protect them from corrosive substances. This layer is not added to them, like a layer of electro-plating. Instead, passivation is formed by dipping the instruments in an acid bath which removes the Nickel and Iron from the top part of the instrument surface. The metal that remains is Chromium, which reacts with the acid to form Chromium Oxide–the passivation layer. This layer is very tough and protects the instrument from corrosion, but this layer is also very thin and can be easily damaged. Once this layer is damaged, corrosive substances can make their way to the steel below. It is, however, possible to reinforce this layer of passivation, and one of the means is to expose these instruments to an acid rinse in the wash cycle.

So to answer your question, the acid rinse will not harm your surgical instruments. In fact, it will strengthen and keep them free from corrosive deposits at the same time. Furthermore, the acid rinse will also keep your washer disinfector chamber free of deposit formations.

What is the best type of water for use in the final Thermal rinse for a Washer-Disinfector?

In my opinion, the best water to use in your final Thermal rinse would be De-Ionized (DI) or Reverse Osmosis (RO) water (I would actually have to say that these two treated waters are best for your whole wash cycle and not just the thermal rinse). DI and RO waters are both lacking in charged inorganic particles; this inorganic material is the main cause of deposits on your instruments. Deposits of calcium, magnesium, chlorides, etc. from tap water not only harm your instruments, but will also end up on the chamber walls, rotary spray arms and heating elements of your washer-disinfector, hampering its performance. Using water that is free of these inorganics, especially in the final thermal rinse, will help prevent these deposits from forming.

If tap water is the main source of water in the rest of the wash cycle, deposits can be alleviated by adding an acid rinse to a rinse cycle just before the final thermal rinse. deconex 25 Organacid™, a low dosing, phosphate and surfactant free, organic acid rinse additive, is a perfect choice for this. Originally formulated as a neutralizing rinse for use after an alkaline wash cycle, deconex 25 Organacid™ used in the rinse cycle will safely keep inorganics from depositing on your surgical instrumentation and washer-disinfector. Used regularly, it will also reduce and eliminate the need to “de-scale” your washer-disinfector.

Our hospital has very hard water that leaves deposits on our instruments. Would water softening help?

Hard water deposits are very bad for both your instruments and your washer disinfector machine (WD).

The deposits on instruments make them more susceptible to corrosion (especially fretting corrosion in the box-lock), damaging the instruments and providing “hiding spaces” for organic soil and micro-organisms. Deposits in your WD eventually impede the machine’s performance by blocking water flow in the washer arms.

Softening your water only exchanges the calcium in your water for sodium. Although this will lessen deposits on your instruments, I recommend that your resources are better spent in getting a water deionization (DI) system.

DI water is void of both positive and negative ions (although it will still contain uncharged matter). This lack of charged matter makes the water hypotonic (water is a universal solvent and being stripped of its charged materials, it becomes aggressive), making it a better cleaning agent. In fact, you would need less detergent in your WD if you used DI water.

Water deionization is more expensive than water softening. Due to this fact (and the general lack of understanding of water and cleaning chemistries), many institutions with DI (or reverse osmosis water–which is even purer) only use DI water in their final thermal rinse cycle. This is to eliminate hard water deposits from the rest of the tap water cleaning process.

I would also suggest if you have a cleaning cycle that employs the use of tap water in all cycles up to the final thermal rinse, you should incorporate an acid rinse in the initial rinse cycle. This will help eliminate any inorganic deposits that may form on your instruments prior to the rinse cycle.

25 ORGANACID™ is just such an acid rinse. A very low dose in your initial post wash rinse will not only neutralize water hardness and prevent it from depositing on your instruments and WD chamber, but will also help remove existing deposits.