Wednesday, November 28, 2012

The EPA is responsible for the impact of commercial chemicals released into the environment. One major concern is the impact some chemicals have on the endocrine system within humans and other animals. The EPA has recently released a list of chemicals that it intends to screen over the next five years for endocrine activity as part of the Endocrine Disruptor Screening Program (EDSP). A more detailed explanation of the EDSP is available. The list of chemicals is also available.

Included on this list are several chemicals well known to people in healthcare sterile processing and food preparation and processing. These include:

Ethylene oxide

Hydrogen peroxide

Peracetic acid



Sodium hypochlorite

Ethanol and


It should be stressed that these chemicals are on the list of 10,000 chemicals awaiting assessment; they have not yet been assessed; and with 10,000 chemicals under consideration, it would probably be hard to identify any chemical with widespread use that is not on the list. Watch this blog for more information as it becomes available.

Tuesday, November 27, 2012

Why Don't More Companies offer a Hydrogen Peroxide Monitor?

Hydrogen peroxide is a widely used chemical, finding application in healthcare for sterilization, metal fabrication mills for pickling and pulp & paper as a bleaching agent. According to Wikipedia, in 1994, world production of H2O2 was around 1.9 million tonnes and grew to 2.2 million in 2006. The hazards of exposure to hydrogen peroxide vapor are well known, the OSHA permissible exposure limit (PEL) for hydrogen peroxide is 1 ppm, calculated as an eight hour time weighted average (TWA) [29 CFR1910.1000 Tbl Z-1], which can be compared to the PELs for some other familiar hazardous gases and vapors: carbon monoxide (50 ppm), Hydrogen cyanide (10 ppm), chlorine (1 ppm ceiling). Hydrogen peroxide is electrochemically active and so it can be detected relatively easily by an appropriate electrochemical sensor.

Hydrogen peroxide is widely used, its vapors are known to be very hazardous, it is relativley easy to detect, but of the many gas detection companies operating the United States (estimated at over 80 at one point), why do so few offer monitors for hydrogen peroxide? We are aware of only three or four including ChemDAQ. The answer is calibration!

There are over twenty gases that monitors are readily available from the gas detection companies including Cl2, CO, H2, HCN. HCl, H2S, NH3, NO, N2O, NO2, SO2, O3 and combustible gases. The common feature that all these gases have in common is that the certified gas mixtures are available from specialty gas companies that can be used to calibrate the respective gas monitors. The availability of a test gas makes the design a monitor much easier. The new monitor will look like an old monitor with new sensor, tweaked circuitry and software and a new label. The sensor is calibrated with a new test and off it goes to a life of productive service. Of course, this is a gross simplification of the work that must be done to release a new product but it illustrates the point.

However, if the calibration gas does not exist, then the gas monitor manufacturer has two choices – find a surrogate gas or generate their own test gas. Many sensors respond to more than one gas and so if the ratio of the responses is constant (cross sensitivity), then calibrating with a gas that comes in cylinder from a specialty gas company, multiplied the cross sensitivity ratio should give a calibration to the new target gas.

The operative word there is ‘should’ because sometimes cross calibration is unreliable. Many hydrogen peroxide sensors give a strong response to sulfur dioxide, but the cross sensitivity can be affected by the environment. We once tested a hydrogen peroxide sensor with both hydrogen peroxide and sulfur dioxide and found that the sensor responded well to sulfur dioxide but gave almost no response to hydrogen peroxide. One of the components in the gas path was removing the hydrogen peroxide. Hydrogen peroxide is much more reactive than sulfur dioxide (stronger oxidizing agent, spontaneously decomposes over time); so the fact that there are contaminants that will react more with hydrogen peroxide than sulfur dioxide should not be very surprising.

Clearly, if this test had been an attempt to cross-calibrate the hydrogen peroxide sensor with sulfur dioxide, the sensor would have tested as normal, even though it barely registered hydrogen peroxide; creating a potentially dangerous situation. Even if the sensor module leaves the factor correctly calibrated, the same problem can potentially occur if the customer then attempts to field calibrate the sensor with a sulfur dioxide or other surrogate gas. After all, how many users have hydrogen peroxide test gas of known concentration readily at hand. Field calibration of reactive gas sensors with less reactive surrogates runs the risk of the sensor appearing to be functioning normally, but not actually detect the target gas.

The role of calibration in any gas monitor is two fold. The first function is a basic check that the monitor is working properly, that it responds to gas when the gas is applied. The second function is to ensure that the sensor reading is accurate. Obviously these two functions are closely related and overlap to some extent.

Since hydrogen peroxide test gas is not readily available, it must be produced by the sensor manufacturer. Hydrogen peroxide can be produced by evaporating hydrogen peroxide solution. There is no great mystery here, the chemical literature describes several way of achieving this goal, but the problem for the manufacturer is to produce a consistent concentration of hydrogen peroxide over time, and to be able to determine what that concentration is.

It may sound simple, and in principle it is, but the folks at ChemDAQ have spent a lot of time and effort engineering this process in order to produce a reliable and accurate calibration method. ChemDAQ generates hydrogen peroxide test vapor from hydrogen peroxide solution and we have our generators run continuously in order to ensure that the system is at steady state. We also regularly titrate the gas stream to measure the hydrogen peroxide concentration so that we know what hydrogen peroxide concentration used it. This hydrogen peroxide test gas is then used to calibrate the hydrogen peroxide sensors.

All of ChemDAQ’s hydrogen peroxide calibrations are performed with hydrogen peroxide test gas. Similarly, all of ChemDAQ’s peracetic acid sensor calibrations are performed with peracetic acid test gas. This approach means that users of our equipment can be assured that their hydrogen peroxide sensors will respond to hydrogen peroxide vapor and the that the readings will be accurate.

If you use hydrogen peroxide and your hydrogen peroxide vapor monitors are not calibrated with hydrogen peroxide test gas, but with another gas such as sulfur dioxide then you may want to question how reliable that calibration is.

Thursday, November 15, 2012

We Don’t Use Hydrogen Peroxide, We Have a Sterrad® Plasma Sterilizer

We often hear refrains similar to that of the title when we discuss hydrogen peroxide monitoring with customers. Thirty years ago, most hospitals used ethylene oxide for their low temperature gas sterilization. In the 1990s, Advanced Sterilization Products (ASP), a J&J company, launched the Sterrad line of sterilizers. This product has been remarkably successful and is now the dominant low temperature sterilizer in the US, and many other countries around the world.

A sterilized product is one that is free of all microbial life, including the highly resilient sporoidal bacteria. Obviously, any chemical gas or vapor that can achieve sterilization poses a risk to anyone exposed to it. Hydrogen peroxide for example has an OSHA permissible exposure limit (PEL) of 1 ppm (8 hr time weighted average), the same as ethylene oxide. The Sterrad line of sterilizers generally has a good safety record, but as with any complex equipment malfunctions can occur, engineering controls can fail and user error can result in potential exposures. Therefore, ChemDAQ recommends gas monitoring for all gas and vapor sterilant chemicals.

The Sterrad sterilizers function by reducing the pressure, introducing hydrogen peroxide vapor (made by evaporating liquid hydrogen peroxide solution) which performs the primary sterilization step, and then the sterilizers activates its radio frequency coils to convert the hydrogen peroxide vapor into a plasma which eliminates residual hydrogen peroxide. The total cycle time for the 100S is about 55 minutes. [100 S data sheet].

As the old saying goes, ‘Time is Money’ and so there is a need for shorter cycle times. Chemical sterilization is achieved by exposing the articles to be sterilized to high concentrations of reactive gases or vapors. Shorter exposure times require higher concentrations of these gases. The NX series of sterilizers takes the 59% solution of hydrogen peroxide used in the 100S and internally concentrates it about 90%. Sterilizing with this solution allows cycle times of only about 28 minutes.

Most matter (solid, liquid, gas) is electrically neutral, but plasma, sometimes described as the fourth sate of matter, is different. Plasmas are found in stars and flames and even fluorescent lights etc., and consist of atoms with at least some of their electrons stripped off forming an ionic gas with lots of high energy, very reactive radicals. While the plasma contributes to sterilization the surfaces of an object, the radicals are so reactive that they would have very limited penetrating power into crevices etc. since they would react with the first surfaces they reach. Therefore the main sterilizing agent in the Sterrad sterilizers is the hydrogen peroxide vapor.

The other main hydrogen peroxide sterilizer used in US hospitals is the V-PRO from Steris Corporation. The Amsco® V-PRO sterilizer forms hydrogen peroxide vapor from a solution of 59% hydrogen peroxide, and also offers a 28 minutes cycle time. The V-PRO generally functions similarly to the Sterrads, though both manufacturers may take exception to this description; but it does not use a plasma to remove the left over hydrogen peroxide at the end of the sterilization cycle. Instead, the hydrogen peroxide is destroyed by passing it through a catalyst that converts it to oxygen and water. The Sterrads have a similar catalyst on their exhaust to remove any hydrogen peroxide vapor surviving the plasma treatment

In 1990 Amsco (a forebear of today’s Steris Corporation) sued Surgikos Inc (ASP was founded as a division of Surgikos) for patent infringement claiming that the Sterrad plasma process was merely icing on the cake and therefore Surgikos were infringing the Steris patent claiming hydrogen peroxide sterilization. [US patent 4,169,123]. Surgikos argued that the plasma process was an essential part of their process, as describe in their own patent [US patent 4,643,876]; and managed to convince the court that they were right. The cynic might claim that this success was more attributable to the skill of Surgikos’s attorneys that hard science; but patent was not infringed as the rest is Sterrad history.

While the technologists may argue whether the plasma phase really increases sterility, one fact is sure, having a plasma phase greatly helps marketing. What a ‘cool’ name: a Plasma Sterilizer!

In summary, both the Sterrad sterilizers and the V-Pro sterilizers use hydrogen peroxide as the sterilant chemical. The plasma phase may contribute to the sterilization, but even ASP say it is primarily there to remove residual hydrogen peroxide vapor. By their very nature, all chemical sterilants are potentially harmful to anyone exposed to them. Even though both Sterrad and V-Pro sterilizers and designed and built to the highest standards, leaks can occur and therefore all chemical sterilizers should be monitored for leaks. Like a fire alarm, major leaks rarely happen, but if they do, you will be glad you had a ChemDAQ monitor there. Amsco® is a registered trademark of Steris Corporation; Sterrad® is a registered trademark of Advanced Sterilization Products.