Xenon disinfection system output, gases, odor question:

At our hospital operating room we are using the Xenex® robot to kill C-diff and other bacterias harmful to staff and future patients. It smells like getting out of a highly chlorinated pool. This exceeds OSHA standards. How do I get the proper department to research this?

This article series discusses the problem of oxidation of building materials from excessive ozone exposure and the horrible chemical smells that may follow such mistakes. We describe how to track down which building materials were over-dosed with ozone and are now giving off a new stink, and we explain how to cure that problem. (Note: other uses of ozone as a disinfectant can be effective and are important in many applications.)

Ozone as Possible By-Product of Xenon Light Disinfection Methods

Reader Question: Xenex® robot in use for hospital disinfection seems to be producing high levels of ozone

31 August 2015 PhilB said:

At our hospital operating room we are using the Xenex® robot to kill C-diff and other bacterias harmful to staff and future patients.

Xenex claims their machine complies with OSHA regulations of .01ppm over an eight hour period. I have to run this ozone generating device 25+ times a night for ten minute cycles. There is a one minute grace period while the light retracts before I am alerted to reenter the room to move it to another spot. 2-3 shots per room every night.

Since I have been running this machine, I have a sore throat during my shift and my eyes burn at the end of the six hour burn-off.

Your article says,"Experimentation has shown that the odor of ozone can be detected and identified by most people at a concentration of from 0.02 to 0.05 ppm (parts ozone per million parts air + ozone)."

It smells like getting out of a highly chlorinated pool. This exceeds OSHA standards. How do I get the proper department to research this?

Reply: Xenon lamp disinfection is not itself an ozone treatment method but might produce ozone gas indoors

Phil, by your accounting you're running the equipment for more than four hours each night.

The Xenex® robot (Xenex Disinfection Services 121 Interpark, Suite 104 San Antonio, TX 78216 Tel: 1-800-553-0069 Website: https://www.xenex.com/) is using "pulsed Xenon" a "UV" disinfection system.

While I'm no expert on UV disinfection by light in hospitals, it is apparent that the hazard and thus the short grace period, is a risk of exposure of the eyes to intense UV light. As long as the light is OFF when you enter the room, the light hazard would not be present. Material I've read on Xenon light disinfection cited no toxic byproducts. More clinical trials may be needed however to study the efficacy of the approach.

Xenon light disinfection is not an ozone disinfection method. Ozone disinfection uses a highly-reactive oxygen molecule O3 to oxidize materials. Xenon disinfection uses millisecond pules of an intense light at 200-320nm wavelength range for 8-12 minutes over 2-3 doses as its disinfection approach.

Ozone production and Xenon light has been discussed and the relationship between light in the UV range and ozone production has been cited by Salvermoser (2003 & 2008) and Schalk (2006) and others.

The influence of water vapor on photochemical ozone generation has been investigated. Tests of a coaxial ozone generator driven by an efficient, tubular, 172 nm xenon excimer lamp revealed that ozone saturation concentration strongly depends on moisture concentration in the process gas.

In order to adequately model the data, catalytic ozone destruction by OH and HO2 radicals formed by reactions with trace amounts of water vapor in the process gas had to be included in the photochemical ozone production rate equation system. Based on the model, optimized ozone photoreactor designs for ambient air, dry air and dry oxygen are described. (Salvermoser 2008)

Depending on the indoor moisture level, Xenon light can be a ozone generator and it seems to me ( a lay person ) that there could be hazards from Xenon light disinfection unless the proper bulb type is employed. The U.S. Army has made a clear and succincct remark on this concern:

Some types of UVGI lamps generate ozone. This can pose a workplace hazard, and only “ozone free” lamps made with doped quartz should be used for
surface disinfection. - (U.S. Army Technical Paper 24-001-1114 2014)

And in the U.K. The Health and Safety Executive has commented on a related and potential hazard that is less immediatly obvious:

projection lamps: high-pressure xenon lamps used in cinema projectors emit some UV radiation and also produce ozone. (HSE Guidance Note #38, 2014)

What these suggest to me is that although Xenon disinfection is described by my earlier comments (and by expert research on the topic) it is possible that the procedure might be generating ozone in the area being treated. I suggest contacting Xenex directly to ask them for guidance on that question. I'm asking the company for advice directly as well. Let me know what you're told as what we learn may assist other readers.

(Sept 6, 2015) PhilB said:

When I spoke to the Xenex rep "Celia" she said the odor was ozone.

I sent an inquiry to Xenex through their website and a Mr. Ed Sylvester called me to explain they were within the legal limits of OSHA standards. 0.01ppm
However, in the above article it states ozone can be detected through the olfactory bulb between 0.02~0.05ppm. Now that is each and every time I use this machine 25+ times every night.
If my math were correct 25 x 0.03= 0.75ppm

(Sept 14, 2015) (mod) said:

Phil,

Based on e-text alone we cannot know what the ozone level is in your building but in general, the sources I've reviewed on this question are in agreement that if you can smell ozone there is probably a higher-than-acceptable ozone level present.

You are right that the low-end of what people can smell is a very low level of ozone indoors - down to 0.02 ppm.

But because ozone is so volatile you cannot assume that it simply accumulates. Depending on the time period between ozone generation, the area volume, concentration and other factors, it is quite likely that by the end of the rest interval the ozone in the area where it was generated is at a much lower level, possibly below the limits of detection.

A more accurate picture is to assume that the ozone level is going up and down during the 15 usage cycles per night - presuming that they are all in the same physical area.

If the ozone is being generated each time in a new area then you cannot add them together to claim a higher exposure level.

But you can assert that if you smell ozone in the work area, you are being exposed to it repeatedly during a work shift. You don't know at what level unless it is measured during the entire time of exposure.

An industrial hygienist with expertise in ozone measurement and exposure standards would be the proper person to consult for an accurate on-site study of what's going on. Unfortunately that's also costly.

Research on relationship between Xenon lamp disinfection & ozone production

• Eliasson, B., and U. Kogelschatz. "Ozone Generation with Narrow–Band UV Radiation." (1991): 365-373.
  Abstract: Ozone formation in oxygen at atmospheric pressure following the photodissociation of O2 molecules in the vacuum UV range is tudied. A new VUV source based on incoherent xenon excimer radiation from a dielectric–barrier discharge provided narrow–band UV radiation at 172 nm with a half–width of 14 nm. The formation of ozone from the initial photodissociation fragments O(3P) and O(1D) is treated theoretically and compared to measurements.
• EH40/2005 Workplace exposure limits: Containing the list of workplace exposure limits for use with the Control of Substances Hazardous to Health Regulations (as amended) Environmental Hygiene Guidance Note EH40 (Second edition) HSE Books 2011 ISBN 978 0 7176 6446 7 www.hse.gov.uk/pubns/books/eh40.htm
• Health and Safety Executive, "Ozone: Health hazards and control measures Guidance Note EH38", EH38 (Third edition) Published 2014, HSE, U.K., retrieved 31 August 2015 original source: http://www.hse.gov.uk/pubns/eh38.pdf - Abstract:
  This guidance is primarily aimed at employers and managers of people exposed to ozone in the course of their work. Other groups, such as employees and health and safety professionals, will also find the guidance useful. It draws attention to the potential ill health which exposure to ozone can cause and indicates potential sources of ozone at work as well as offering advice on the precautions you may need to take to prevent or control exposure.
• Pavlovich, Matthew J., Hung-Wen Chang, Yukinori Sakiyama, Douglas S. Clark, and David B. Graves. "Ozone correlates with antibacterial effects from indirect air dielectric barrier discharge treatment of water." Journal of Physics D: Applied Physics 46, no. 14 (2013): 145202.
• Roth, J. Reece. Industrial Plasma Engineering: Volume 2-Applications to Nonthermal Plasma Processing. Vol. 2. CRC Press, 2001.
• Salvermoser, Manfred, Daniel E. Murnick, and Ulrich Kogelschatz. "Influence of water vapor on photochemical ozone generation with efficient 172 nm xenon excimer lamps." Ozone: Science and Engineering 30, no. 3 (2008): 228-237.
• Salvermoser, M., and D. E. Murnick. "High-efficiency, high-power, stable 172 nm xenon excimer light source." Applied physics letters 83, no. 10 (2003): 1932-1934.
• Schalk, Sven, Volker Adam, Erich Arnold, Karl Brieden, Alex Voronov, and H. D. Witzke. "UV-lamps for disinfection and advanced oxidation–Lamp types, technologies and applications." IUVA news 8, no. 1 (2006): 32-37.
  Excerpts: Since ozone is produced via 185 nm radiation in combination with oxygen from ambient air, the UV/O3 process does not necessarily need an external ozone source. In aqueous solutions, the 185 nm radiation is absorbed almost exclusively by water, bringing about its photolysis to yield ·OH radicals and ·H atoms.
  
  ... The preferred envelope material for Standard Low Pressure Lamps is Fused Quartz. Due to the generally low wall temperature, it is also possible to use Softglass (SodiumBarium-Glass). Softglass Lamps have a similar design as Fluorescent Lamps known from general lighting. The UVSoftglass does not transmit at 185 nm, hence all these lamps are “ozone-free” lamps.
  
  In contrast to Softglass Lamps, standard Quartz Lamps are available in both “ozone-free” (G, GPH lamps) and ozonegenerating (G…VH, GPH…VH – VH stands for Very High ozone) versions. As seen in Table 1, both the specific UVC-flux per unit arc length and the UVC efficiency are higher for the Fused Quartz types. This is caused by the lower transmittance of Softglass compared to Fused Quartz at 254 nm.
• Shintani, Hideharu, Akikazu Sakudo, Peter Burke, and Gerald McDonnell. "Gas plasma sterilization of microorganisms and mechanisms of action (Review)." Experimental and therapeutic medicine 1, no. 5 (2010): 731-738.
• U.S. Army, "Effectiveness and Safety of Ultraviolet Germicidal Irradiation Lamps Used for Disinfecting Surfaces Contaminated with the Ebola Virus", Technical Information Paper No. 24-001-1114, retrieved 31 August 2015, original source http://phc.amedd.army.mil/PHC%20Resource%20Library/TIP_No_24-001-1114_Effectiveness_and_Safety_of_UVGI_Lamps.pdf Excerpt:
  Some types of UVGI lamps generate ozone. This can pose a workplace hazard, and only “ozone free” lamps made with doped quartz should be used for
  surface disinfection.
• US Occupational Safety and Health Administration OSHA Analytical Methods Manual 2nd Edition Method 10-214: Ozone in work place atmospheres
  (impregnated glass fiber filter) USDOUOSHA Salt Lake City 1995
• Wang, Ding, Thomas Oppenländer, Mohamed Gamal El‐Din, and James R. Bolton. "Comparison of the Disinfection Effects of Vacuum‐UV (VUV) and UV Light on Bacillus subtilis Spores in Aqueous Suspensions at 172, 222 and 254 nm." Photochemistry and photobiology 86, no. 1 (2010): 176-181.
• Zoutman, Dick, The Pros and Cons of Alternative Disinfection Technologies for Room Decontamination (Powerpoint presentation), www.virox.com/files_docs/content/pdf/msds/CHICAPresentation4.pdf

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