The Consumer Product Safety Commission (CPSC) is trying to answer this question. Their study and the responses to that study highlight the complexity of the issue.
As the sales of air cleaners have increased over the past 10 years a serious question has been raised about products that generate ozone as a byproduct. What level of ozone is “safe” for users? Unfortunately, no Federal agency has adequately addressed this issue. The EPA has said their regulatory responsibility is with outdoor ozone – not ozone found indoors. The FDA has a regulation for medical devices that they should not produce more than 50 parts per billion (ppb) of ozone. The Consumer Products Safety Commission (CPSC) has not established a regulation. Since the CPSC would seem like the most suitable federal agency for such action, they commissioned a study to determine what level of ozone emission would be safe for consumers. This study and, more importantly, the responses to the study represent some of the best information available on the limits for ozone emissions from air cleaners.
The study was conducted by Dr. Richard Shaughnessy of the University of Tulsa – a noted expert on indoor air quality. It’s purpose was to assess the adequacy for protection of human health of an ozone concentration in indoor air of 50 ppb. The assessment was to include a review of the relevant scientific and technical literature to evaluate the likelihood of health effects at that concentration. This assessment was sub-contracted to Drs. David Krause (PhD) and Lauren Ball (DO)- both public health professionals. If the 50 ppb level was found to be adequate, then corresponding maximum release rates for various room sizes were to be calculated.
The authors of the study found that there really were not any controlled studies on animals or humans at indoor ozone levels less than 50 ppb. They found that “human studies have been largely epidemiologic studies using data from outdoor monitoring, and experimental protocols have focused on levels in the range of 80 ppb to 120 ppb. Therefore, the existing information is not sufficient to characterize the dose-response relationship for ozone at levels below 50 ppb.” However, the authors mentioned that the epidemiological studies did show associations between incremental increases in ozone concentrations and adverse health effects.
The contract for the study also required the authors to consider the potential health effects of ozone on sensitive populations, such as young children or individuals with pre-existing respiratory conditions such as asthma, emphysema and COPD. While the authors recognized that even small changes in lung function through exposure to ozone could be a problem for those with respiratory illnesses, there was not sufficient data to suggest the need for establishing a different ozone accumulation level for sensitive populations. However, they did state that it would be reasonable to consider a margin of safety in setting an exposure standard for certain subpopulations. Finally, the authors of the study cautioned that their conclusions “were based on currently available information and may be subject to change as new data becomes available.”
Since the authors determined that the 50 ppb of ozone appeared to be adequate, Dr. Shaughnessy conducted his part of the contract to determine what level of ozone (in mg/hr) could be emitted from an air cleaner not to exceed the 50 ppb steady state air concentration level. Holding all other inputs constant, and assuming no other sources of ozone, he provided maximum ozone release estimates for several room sizes, representing small bedrooms to more spacious master bedrooms in large homes. The Shaughnessy model estimated that ozone releases from an air cleaner should not exceed approximately 14 to 26 milligrams (mg) of ozone per hour of operation.
The CPSC staff reviewed the study in a report dated 9/26/2006. In their report they explained that they had established contracts with two experts to review the report. Both reviewers had some issues with various parts of the report. These included a concern of not enough weight being given to the epidemiological studies and not enough emphasis on the health effects of the products of the ozone reaction with other chemicals in the room. Both reviewers had concerns that the 50 ppb did not provide enough margin of safety for asthmatic children. The reviewers also had some additional comments on the modeling part of the report and some suggestions on modifications.
CPSC staff stated that they agreed with the study’s conclusions that “50 ppb represents a level below which the occurence of adverse health effects have not been demonstrated in healthy subjects in controlled ozone research,” and that evidence to adjust this level, either upward or downward is not compelling. “Thus, the contract report’s recommendation to continue to use the 50 ppb level appears to be reasonable, especially for the development of voluntary standards to limit emissions of ozone from air cleaners.” (Note: They did not call for action by the Commission.) CPSC staff went on to say they did not have any comments on the report’s recommendation to consider a margin of safety for sensitive subpopulations. The report and the CPSC staff conclusions were then posted for public comment. And this is where the story becomes very interesting.
Unlike many government reports that receive few, if any, comments, this study received over 80 pages of public comments. Comments were received from Consumer’s Union, AHAM, the California Air Resources Board, the Asthma and Allergy Foundation of America – Texas Chapter and Dr. Richard Corsi of the University of Texas at Austin. Dr. Corsi is also a noted expert on indoor air quality and indoor air chemistry. His “comments” exceed 50 pages and represent one of the most thorough and encompassing works on the potential dangers of indoor ozone created by air cleaners.
Dr. Corsi points out that the premise of the CPSC study is to find information that would prove that the 50 ppb standard is not safe. The assumption is that at some point in the past a study or some research was done to determine that the 50 ppb was safe and that the FDA established their regulations based on these findings. As it turns out this is a bad assumption. There was no research. As stated in the Federal Register of June 27, 1972, the 50 ppb of ozone was “recommended” by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). It was not based on a medical study. It was an arbitrary recommendation based on the fact that the outdoor limit at that time was 100 ppb and that the indoor limit should be much less than that. Yet, it has become the standard. Who could have ever imagined this 35 years ago?
Corsi goes on to explain that there are studies that have been done that raise serious concerns about the safety of adding ozone to indoor air. Small increases in ozone have been shown to have significant effects on mortality, asthma symptoms and respiratory discomfort. For example, Dr. Michelle Bell of Yale University found in her study published in the Journal of the American Medical Association (JAMA) in 2004 that just a 10 ppb increase in environmental ozone caused a 0.52% increase in mortality or about 4,000 deaths per year. In another study published in Environmental Health Perspectives, Bell, et. al. found that there were significant health effects for ANY increase in ozone – even less than 10 ppb. Gent, et.al. also in a JAMA article in 2003 found that increases in ozone of 50 ppb were detrimental to children with asthma. These increases resulted in a 35% increase in likelihood of wheeze and a 47% increase in chest tightness. Triche, et. al. in an article in Environmental Health Perspectives in 2006 found that infants (especially those with asthmatic mothers) had significant increases in wheeze and breathing difficulties with small increases in ozone at or below EPA standards.
All of the above studies are based on outdoor ozone measurements. Even though some of the studies are mentioned in the CPSC report, they are not considered because of this fact. Corsi argues that these studies and others are relevant and “on point.” There are several reasons for this. First, people spend 90% of their time indoors. Secondly, indoor ozone levels track outdoor ozone levels. (Indoor levels run between 20% and 70% of outdoor levels.) The prolonged indoor exposure is a more important factor in determining health effects than the few minutes a day spent outdoors in elevated ozone conditions. (The infant study of Triche, et. al. supports this position. Babies spend more than 90% of their time indoors.)
Corsi points out that the indoor ozone level is only one aspect of the health effects equation. Ozone is a very reactive gas. Because of this it initiates substantial amounts of indoor air chemistry. Ozone reacts readily with various volatile organic compounds (VOC’s) to create other undesirable byproducts. Two of the major outcomes of this indoor air chemistry are formaldehyde (a known carcinogen) and secondary organic aeresols (ultrafine particles). To assess the effects of elevated indoor ozone levels Corsi included the ozone itself – but also the formaldehyde and the ultrafine particles. All three can have a detrimental effect on human health.
By using a sophisticated modeling program including such factors as room size, air exchanges, levels of VOC’s such as terpenes and linalool alcohol, outdoor to indoor ozone transfers, and reaction rates for the indoor air chemistry, Corsi was able to calculate maximum ozone emission rates for a residence, an office and a school. This was done for a “best case” where individuals in these settings would have normal respiratory function and for a “worst case” where individuals would be from the sensitive populations of the young, the elderly and those with respiratory diseases such as asthma and COPD. What he found was that the “best case” scenario allowed for an ozone emitting air cleaner to produce 17.5 mg/hr of ozone in a home (whole house), 1.3 mg/hr in an office and 9.9 mg/hr in a school. In the “worst case” scenario where the air cleaners would be used around people in the respiratorially sensitive population the ozone producing air cleaner was allowed to emit 0.45 mg/hr of ozone in a home, 0.041 mg/hr in an office and 0.13 mg/hr in a school.
In his cover letter to the CPSC Corsi summarized these findings by saying: “it is my opinion that standards for the protection of the general public should be focused on an incremental increase in ozone concentration of 5 ppb (at most) and less than 5 ppb to protect those most sensitive to ozone and its reaction products.”
The biggest problem with the CPSC report is that it does not take into consideration the fact that the majority of people who purchase an air cleaner do so because of allergies, asthma, other respiratory diseases or some other health concern. (see California Air Resources Board survey of air cleaner owners.) These are just the people (as Dr. Corsi’s report illustrates) who are the most susceptible to the ill effects of ozone and ozone chemistry generated byproducts. It is logical for them to assume that if they purchase an air cleaner, it will perform as an air cleaner and not create air that might be detrimental to their health. It does not appear that the CPSC report adequately protects this sensitive population.