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Hazardous Materials > Air Quality Monitoring > Health Facts
Health Facts about Air ToxicsFrequently Asked QuestionsGeneral
Potential Health Impacts
What chemicals are toxic?
These doses that define the low limits of the toxic effects are not absolute; they are different for every person. For example, alcohol has little effect at low doses, and has what some describe as therapeutic doses in the middle. But alcohol can be fatal at high doses. People of Asian descent are genetically less able to metabolize alcohol, and they suffer the toxic effects at markedly lower amounts than persons of European descent. In that sense, Asians would be described as sensitive and Europeans as resistant. The point is that there are no chemicals that are inherently safe or unsafe. There are only doses that are safe for most people and doses that are unsafe for most people. What does dose mean?The amount of a chemical that is absorbed or inhaled is called the dose. The dose depends on two factors: (1) The amount of the chemical, and (2) the length of time you?re exposed. This is to say that the ceiling of the safe range of exposures could be exceeded by the amount of a chemical (too much chemical) or the length of exposure time (too much time), or both. When we try to determine the safe amount of a chemical, we usually assume the worst-case; that is, if you breathed the chemical 24 hours a day, 7 days a week, over the 52 weeks of a year. That way, we can be sure we don't underestimate the dose. Safe amounts of some chemicals are also determined for one-time exposures at shorter periods. The other aspect of determining the dose is the concentration. In regard to air quality monitoring around the ConocoPhillips-Rodeo refinery, these concentrations are determined by instruments at the facility's fenceline. The instruments record both peak levels and the averages over various periods of time. The health effects from a particular chemical is usually more proportional to longer-term average concentrations. But there are exceptions, so both peak levels and average levels are reported for this facility. What are alarm levels about?The community in the vicinity of the ConocoPhillips-Rodeo refinery has established alarm levels for many of the chemicals originating at the facility. The levels are designed to provide an early warning in the event that the amount of a chemical in the air is increasing. In some cases, the alarm level is a predictor of health problems for a short-time exposure; in other cases, it only warns of a change in conditions at the plant, which may precede noticeable odors. The chemical-specific FAQ information below identifies which chemicals cause health problems. The high alarm level settings for concentrations that have been established for most of the hydrocarbons are based on 10% of their lower flammability limit, since most of these chemicals are not considered toxic. For butane, there is a factor of 17,000 between the minimum detectable level and the high alarm level for concentration. How were the alarm levels decided?The high alarm level for concentrations are set based on where transient health effects from these chemicals may start occurring in people. The concentrations were established based on toxicity data and established concentration levels available from the Office of Environmental Health Hazard Assessment, the National Academy of Sciences, and the Occupational Safety and Health Administration. Also, Levels of Concern available from the U.S. Environmental Protection Agency were considered. The levels at which the concentrations of chemicals can be measured by the ConocoPhillips-Rodeo refinery fenceline monitors are magnitudes lower than the established alarm levels for concentration. There is a factor of 50 between the minimum detectable level for formaldehyde, 71 for carbonyl sulfide, 800 for 1,3-butadiene, 8,333 for ammonia, and 15,000 for methyl-tert-butyl ether (MTBE) and the high level for concentration alarm settings. What are odor thresholds?Many of the chemicals listed on this website have an odor threshold (i.e., the concentration of a chemical at which people can start to smell it) that is well below the alarm setting. For instance, most people can start smelling hydrogen sulfide, which smells like rotten eggs, at 8 parts per billion. The concentration of concern (the high alarm level for concentration) for hydrogen sulfide is 15 parts per million. The difference is a safety factor of almost 2,000. Many people may feel nausea from smelling hydrogen sulfide and other chemicals that may come from the ConocoPhillips-Rodeo refinery, but in most cases there will be no other health effects at the odor threshold. Tunable diode laser (TDL) monitors along the refinery fenceline measure for hydrogen sulfide. However, the measurements at the concentrations reported by the TDL monitors are not sufficiently accurate that Contra Costa County is willing to report them on this website. (Hydrogen sulfide is also monitored by the Bay Area Air Quality Management District as part of its regional air quality monitoring program.) Why measure ammonia?Ammonia is a primary eye and upper respiratory tract irritant. An unpublished study conducted by the Detroit Department of Health and cited by the American Conference of Governmental Industrial Hygienists (ACGIH) (1986/Ex. 1-3, p. 27) reports that ammonia concentrations in the range of 20 to 25 parts per million (ppm) elicited complaints of discomfort from workers engaged in blueprinting and copying operations. In addition, a study of pigs conducted by Stombaugh et al. (1969) appeared to demonstrate that exposure to ammonia also causes systemic effects. Thus the ACGIH established both an 8-hour standard of 25 ppm to protect against chronic effects and a 35-ppm short-term standard to protect against ammonia?s irritant effects. A high alarm level of 100 ppm has been established, and a low alarm level of 3 ppm. Typically, the maximum daily concentrations at the ConocoPhillips-Rodeo refinery fenceline are below 0.05 ppm. Why measure butane?The problem with butane isn?t so much that it's toxic, but that it's explosive at high concentrations. It may also be an indicator of problems that are occurring at the ConocoPhillips-Rodeo refinery if other chemicals are being released that may be more toxic than butane and that may not be measured by the monitors at the fenceline. The high alarm level set by the community is about one-tenth of what would be necessary to start a fire (1,000 parts per million, ppm), and the low alarm level (800 ppm) is set to provide an early warning that levels are increasing. The low alarm level has no health significance, but it is the ?safe? level used by the National Institute for Occupational Safety and Health (NIOSH). The primary risk of exposure to butane is narcosis, which occurs at high exposure levels. Exposure to 10,000 ppm butane for 10 minutes causes drowsiness, but there are no reports of systemic toxicity or irritation at this level (Gerarde 1963a, as cited in American Conference of Governmental Industrial Hygienists [ACGIH] 1986/Ex. 1-3, p. 10). In most cities in the United States, butane is not detected very frequently. Along the perimeter of the ConocoPhillips-Rodeo refinery, levels at the north fenceline are usually higher than those at the south fenceline. But levels are usually below 1 ppm. Why measure carbon monoxide?Carbon monoxide is a colorless and odorless gas that blocks your blood?s ability to carry oxygen. Because of this, carbon monoxide exposure can be fatal at high doses. Various organizations have set acceptable upper limits for humans. People can breathe higher amounts for shorter times without a harmful effect, but people with heart or lung diseases will be more susceptible to poisoning. The U.S. Environmental Protection Agency (EPA) says that 35 parts per million (ppm) is safe for short periods, and that 1,000 ppm is cause for immediate evacuation of the area. Most home carbon monoxide alarms will start to go-off at about 100 ppm. EPA expects that levels of 9 ppm will be safe over the long term. The average level for most large cities is about 1 ppm. At the ConocoPhillips-Rodeo refinery, the maximum levels each month are about 1 ppm, which is about the same as in most cities in the United States. People who smoke cigarettes get carbon monoxide from the smoke, and they average about 35 ppm in their blood. Because of this, they could be affected by lower levels in the air than nonsmokers. Why measure carbonyl sulfide?This chemical gets converted to hydrogen sulfide in your blood. Hydrogen sulfide causes many of the same symptoms as carbon monoxide because it works the same way. It also binds to the oxygen-carrying pigment in blood (called hemoglobin) and, like carbon monoxide, prevents hemoglobin from carrying oxygen around the body. There are no U.S. Environmental Protection Agency (EPA) standards for carbonyl sulfide or hydrogen sulfide in the air outside, but the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) think 10 parts per million (ppm) is safe for short periods, while 100 ppm is considered very dangerous. The 1986 American Conference of Governmental Industrial Hygienists (ACGIH) documentation (Ex. 1-3, p. 318) cites several reports (Brieger 1964; Kranenburg and Kessener 1935; Masure 1950; Elkins 1950a/Ex. 1-953) on the occurrence of adverse ocular effects, including conjunctivitis, associated with exposure to 20 ppm or less of hydrogen sulfide. A study by Poda and Aiken (1966/Ex. 1-115) reported that the adoption of a voluntary limit of 10 ppm in two heavy-water plants eliminated exposure problems. An early study by Flury and Zernik (1931f, as cited in ACGIH 1986/Ex. 1-3, p. 318) reported that conjunctivitis was caused by exposure to 10 to 15 ppm of hydrogen sulfide for 6 hours endured for several days; however, OSHA is unaware of cases in which this substance caused irreversible eye damage. NIOSH relied essentially on the studies discussed above (Poda and Aiken 1966/Ex. 1-115; Flury and Zernik 1931f, as cited in ACGIH 1986/Ex. 1-3, p. 318) when recommending its limit for hydrogen sulfide of 10 ppm for 10 minutes; NIOSH (Ex. 8-47, Table N7) continues to recommend this ceiling for hydrogen sulfide. Along the fenceline of the ConocoPhillips refinery, carbonyl sulfide is rarely detected by the FTIR monitors. Additionally, this chemical decomposes to hydrogen sulfide, which has an odor threshold that is well below the alarm setting. (See the FAQ on What are odor thresholds?) Why measure formaldehyde?Formaldehyde causes cancer in people at high doses. The National Institute for Occupational Safety and Health (NIOSH) considers formaldehyde to be a potential occupational carcinogen as defined by the Occupational Safety and Health Administration (OSHA) carcinogen policy [29 CFR 1990]. NIOSH considers short-term exposures safe at levels up to 0.016 parts per million (ppm) for 8 hours, or 0.1 ppm for 15? minutes. There are no U.S. Environmental Protection Agency (EPA) standards for formaldehyde in the air outside. In most cities, it is found in the air in low amounts. In rural areas, it's probably about 0.0002 ppm; in the suburbs, about 0.002 ppm; in big cities, up to 0.02 ppm. Often there is more formaldehyde inside buildings than outside because of its use in plywood, particleboard, new carpets, new paints, and fingernail polish. Along the fenceline of the ConocoPhillips-Rodeo refinery, it has not been detected by the monitors yet (as of summer 2002). Why measure methane?The problem with methane isn't so much that it's toxic, but that, like butane, it's explosive at high concentrations. The high alarm level set by the community is about one-tenth of what would be necessary to start a fire (5000 parts per million [ppm]), and the low alarm level (1000 ppm) is set to raise an early warning that levels are rising. The low alarm level has no health significance. In most cities in the United States, methane is detected frequently. Typically levels are below 1 ppm, except near landfills and some wetlands. Along the perimeter of the ConocoPhillips-Rodeo refinery, levels at the north fenceline are usually slightly higher than at the south fenceline, but levels are usually below 2 ppm. Why measure methyl tert-butyl ether?This chemical, often abbreviated MTBE, is added to gasoline to make it burn cleaner. The problem is, spills and leaks from underground gas tanks have contaminated the water supply of some communities. Information on human exposure to MTBE is limited. Humans are acutely exposed to MTBE as a part of a medical treatment to dissolve cholesterol gallstones (Thistle, 1992). Injection of the gall bladder with a high dose of MTBE can be associated with several types of health effects (e.g., nausea, vomiting, sleepiness). Minor transient mucosal damage in the gallbladder has been demonstrated with extensive exposure, but no clinically significant consequences have been reported. One patient has been reported to develop intravascular hemolysis and renal failure following inadvertent extravasation of a large bolus of MTBE (Ponchon et al., 1988). Reliable data from epidemiology studies of human exposure to airborne MTBE are not currently available. Rats exposed to 400 parts per million (ppm) for long periods exhibited no adverse health effects. The alarm levels set by the community are early indicators of potential health problems. The low alarm level is 40 ppm and the high alarm level is 200 ppm. Along the perimeter of the ConocoPhillips-Rodeo refinery, typical annual peaks are about 0.1 ppm. Why measure nitrous oxide?Oxides of nitrogen are formed anytime something is burned. Most of it comes from burning gas in cars and trucks or from power plants burning coal or natural gas to make electricity. Nitrous oxides irritate your lungs and can cause a number of health problems. This oxide of nitrogen is much less dangerous than nitrogen dioxide, which is a major problem in many U.S. cities. Nitrous oxide is sometimes called laughing gas and is used in the dental profession as an anesthetic. It is measured along the perimeter of the ConocoPhillips-Rodeo facility as an early indicator that something wrong has occurred at the refinery. The warning levels are set at 999 parts per million (ppm). Peak levels at the north fenceline are around 1 ppm, with about half of that also present at the south fenceline. Why measure ozone?Ozone is one of the ingredients in smog. When it's in the upper atmosphere, ozone is beneficial because it protects us from dangerous ultraviolet light. In the lower atmosphere, ozone is highly injurious at concentrations as low as a few parts per million (Stokinger 1957/Ex. 1-97). A study in which young mice were exposed to 1 ppm ozone for 1 or 2 days reported damage to alveolar tissue (Bils 1970/Ex. 1-58). Human populations chronically exposed to lower concentrations of ozone have been observed to have changes in lung function. In one study, human volunteers exposed to 0.5 ppm ozone for 3 hours per day, 6 days per week, over 12 weeks showed significant changes in lung function (Jaffe 1967/Ex. 1-101). Other investigators reported a 20-percent reduction in timed vital capacity in persons exposed to average concentrations of ozone of 1.5 ppm (range not indicated) for 2 hours (Griswold, Chambers, and Motley 1957/Ex. 1-128). Welders exposed to maximal ozone concentrations of 9 ppm were observed to have pulmonary congestion (Kleinfeld and Giel 1956/Ex. 1-120). The maximum allowed by law in workplaces is 5 ppm. People with poor diets (low in antioxidants) or poor health may be predisposed to injury at lower concentrations than healthy people. Most cities have problems with ozone; however, it now rarely exceeds 0.15 ppm. Cities are now moving toward an 0.08 ppm 8-hour EPA standard, which many of them exceed on days favorable for ozone formation (hot and sunny). Along the perimeter of the ConocoPhillips-Rodeo refinery, conditions at the north fenceline are about typical for what would be expected for a large municipality. The peak levels at the south fenceline are generally higher.
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