Abstract 3
Carbon Monoxide (CO) Properties and Uses 4
Sources of CO Emission and Toxicokinetics 4
Exposure Limits for CO, Sampling and Analysis 6
Protocols for Industrial CO Sampling and Analysis 6
Carbon Monoxide in Substance Priority List (SPL) 7
CO Contaminated Superfund Site 8
Carbon Monoxide Explosion Case Study with Recommendations 8
References 10
Abstract
Carbon Monoxide (CO) is a colorless, odorless gas, which results from incomplete combustion of carbon containing fuels, and has several applications such as effective reducing agent and manufacture of various hydrocarbons. CO is a major indoor air pollutant, and is released when combustion is carried out in confined spaces such as mines or tunnels. CO affects oxygen carrying capacity of blood, causes hypoxia, and affects cardiovascular system, lungs, blood, and central nervous system. Occupational Safety and Health Administration’s (OSHA’s) permissible exposure limit is 50ppm for 8 hour TWA, and CO concentration can be monitored suing direct CO data loggers or using the gas chromatography, and ionizing and detection techniques. CO is ranked 182 in the substance priority list with a toxicity score of 682.3, and Superfund sites such as Centralia, in Pennsylvania, and several landfill sites in US are contaminated with high atmospheric CO concentrations. Additionally, facilities such as Carbide Industries, also report CO induced explosion incidents. Proper safety procedures, usage of PPE, evacuation systems and emergency response plans are essential to minimize loss to human life from CO pollution.
Carbon Monoxide
Carbon Monoxide (CO) Properties and Uses
Carbon Monoxide is a colorless, odorless gas with the chemical formula CO. It is a product of incomplete combustion of carbon containing fuel, and the compound’s molecular weight is 28 (OSHA, 1976). Its auto-ignition temperature is 609°C, however, CO stored under high-pressure or in contact with strong oxidizers can cause fire and explosion (NIOSH, 1978). CO is a major component of producer gas and water gas, which are important fuels used in industrial operations (Newton, 2016). Carbon monoxide is used as an effective reducing agent to convert iron oxides back to metallic iron, as well as in the Mond process of separating nickel from metal ores (Newton, 2016). Hydrogen and carbon monoxide are also used as raw materials in the manufacture of various hydrocarbons, and their oxygen derivatives through the Fischer-Tropsch process (Newton, 2016). Additionally, CO is also obtained as a by-product in certain reactions such as formation of calcium carbide from lime and coke.
Sources of CO Emission and Toxicokinetics
CO emissions occur during welding or combustion in confined spaces, mines and tunnels, in metallurgy industries and foundries, as well as from internal combustion engine exhausts of vehicles (OSHA, 1976). CO is also a major indoor air pollutant, and sources within the home environment include unvented kerosene and gas space heaters, leaking chimneys and furnaces, wood stoves and fireplaces, generators and gasoline powered equipment, as well as automobile exhaust from attached garages (EPA, 2016).
CO exposure can occur through inhalation, as well as through skin or eye contact with the liquid form. Target organs mainly affected by CO include cardiovascular system, lungs, blood, and central nervous system (CDC, 2016). CO causes hypoxia i.e. it combines with hemoglobin of blood, forming carboxy-hemoglobin (COHb), which reduces oxygen carrying capacity of blood (NIOSH, 1978). Also CO has 210-240 times more binding affinity for hemoglobin compared to oxygen.
Acute effects of CO poisoning include headache, dizziness, nausea, palpitations, confusion, visual disturbance and muscle twitch. However, these symptoms do not manifest at CO concentration levels below 70ppm (New Hampshire Department of Environmental Services [NHDES], 2007). Exposure to 500-1000ppm CO i.e. blood concentration up to 15% can result in brain damage (OSHA, 1976) and at 800ppm death can result in 2 hours (NHDES, 2007). Exposure to high dosage of 4000ppm leads to coma and cerebral edema (OSHA, 1976). Chronic exposure to low doses of CO leads to flu like symptoms including headache, sensitivity to light and odor, and can often be misdiagnosed (NHDES, 2007). CO percentage in an average non-exposed person is about 1% (result of normal hemoglobin metabolism), and in a smoker it might be 3-10%. CO percentage in blood above 60% leads to intoxication and death (OSHA, 1976). CO concentration in the atmosphere, corresponding COHb values and clinical effects are tabulated in Table 1. When pregnant women are exposed high doses of CO, the fetus can have brain damage, and prolonged exposure to doses higher than 100ppm during gestation can result in decreased birth weight of infant as well as delayed brain development (NHDES, 2007).
Exposure Limits for CO, Sampling and Analysis
Exposure limits for workplaces, as well as for ambient air are established to ensure adverse human health impacts are minimized. Occupational Safety and Health Administration’s (OSHA’s) permissible exposure limit for CO is 50ppm time weighted average value for an 8-hour work shift (EPA, 2016), and worker should be immediately removed from the workplace if CO concentration exceeds 200 ppm ceiling value in 5 min (OSHA, 1993). The National Institute for Occupational Safety and Health (NIOSH) has set recommended exposure limit (REL) for carbon monoxide at 35 ppm as an 8-hour time weighted average (TWA). The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned a threshold limit value (TLV) of 25 ppm as a TWA for a normal 8-hour workday and a 40-hour workweek (EPA, 2016). EPA’s ambient air quality standards has set a limit of 9ppm for CO for a time period of 8 hours, 35ppm limit for an exposure time of 1 hour (EPA, 2016).
Protocols for Industrial CO Sampling and Analysis
CO levels in the workplace or indoor air environment can be detected through direct reading CO monitors, as well as through sampling and offsite laboratory analysis using gas chromatography (GC), and discharge ionization detector (DID) equipment (OSHA, 1993). Direct CO monitor is a data logger that consists of 3-electrode electrochemical sensor, filter cap and a LCD display (OSHA, 1993). The instrument detects CO concentration in the range 0-999 ppm, and is not capable of detecting instantaneous CO release of concentration greater than 999ppm, also the sensor detects accurately only at a gas flow rate of 0.2L/min (OSHA, 1993). At higher flow rates, the data logger gives higher concentration readings due to pressure differences. OSHA recommends the direct CO data logger for monitoring indoor air quality in homes and small facilities (OSHA, 1993). The GC-DID technique is ideal for large workplaces, with access to laboratory facilities. Gas sample is collected in a multi-layered gas sample collection bag, and the sample is fed into a silica gel or alumina pre-column to filter out carbon dioxide, methane, water or other interfering gases, before passing through a molecular sieve column that efficiently separates hydrogen and methane from CO (ATSDR, 2012). In a second chamber helium is passed through an ionizing discharger that generates high-energy photos (ATSDR, 2012). The photons ionize CO separated in the sample stream, and a detector measures the level of ionization, which is proportional to CO concentration in the sample stream (ATSDR, 2012).
Carbon Monoxide in Substance Priority List (SPL)
The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), requires US Environmental Protection Agency (EPA) and Agency for Toxic Substances and Disease Registry (ATSDR) to prepare a substance priority list (SPL) of various hazardous substances found in the Superfunds sites (ATSDR, 2014). These sites are contaminated and listed under the National Priorities List for remediation, and the SPL substances are ranked based on their toxicity, frequency of occurrence at the site and their potential for causing adverse human health effect (ATSDR, 2014). CO is ranked 182 in the list with a score of 682.3 (derived based on ignitability and reactivity score of 100, mammalian toxicity of 5000 and chronic toxicity score of 1000) (ATSDR, 2014). CO is not carcinogenic but its potential to cause serious human health impacts and lethality has enlisted this substance on SPL. The SPL is updated every 2 years and the rankings are revised or retained for the substances (ATSDR, 2014).
CO Contaminated Superfund Site
One of the Superfund sites greatly affected by CO pollution is Centralia, in Pennsylvania. It was once an active coal-mining town supporting more than 2000 people (Bellows, 2006). In 1962, few workers set fire to a dump of garbage in an abandoned pit, which accidentally set fire to a vein of coal deposit (Bellows, 2006). Though the superficial fire was put off, the fire continued to burn underground in the mines. Pennsylvania’s Environmental Resources officials dug bore holes to gauge the extent of fire, but the wells fuelled the fire (Bellows, 2006). Also, most residents in Centralia were affected by carbon monoxide poisoning, which required immediate abandonment of the town (Bellows, 2006). In 1970 seven years after the fire started, a gas station owner found gasoline heated in the storage tank to 180 F (Bellows, 2006). This was followed by appearance of sinkholes due to fire induced land subsidence, and the government has spent 42 million USD in relocating the residents (Bellows, 2006). The fire is still not extinguished, and CO concentrations of 1000ppm and 2200ppm have been recorded in various sites of Centralia’s cemetery front (Stracher, 2007, p.266). Several other landfill sites and contaminated sites on the NPL report CO emission at toxic levels, and EPA takes efforts to remediate the sites.
Carbon Monoxide Explosion Case Study with Recommendations
The US Chemical Safety and Hazard Investigation Board (CSHIB) reports the case of an electric arc furnace explosion that occurred in Carbide Industries, LLC, Louisville, KY. The explosion that took place on March 21, 2011, killed two workers and injured 2 others (2011). The industry manufactures calcium carbide and supplies it to iron, steel and acetylene industries (CSHIB, 2011). An electric arc furnace (EAF) was employed in Carbide Industries to heat lime and coke mixture to a temperature above 4100F using electricity generated heat. In the furnace molten calcium carbide is formed, which is later cooled solidified and sold, and CO is formed as a byproduct (CHIB, 2011). The chemical reaction is depicted in Fig 1.
Fig1. Calcium Carbide Manufacture from Lime and Coke (Source: CSHIB, 2011)
The facility was 5 storied, and the furnace was located at the ground floor. Control room was located in the second floor (CSHIB, 2011). Coke and lime were fed into the furnace through conveyor systems located on the 5th floor, and molten calcium carbide was collected in a tank (CSHIB, 2011). Electrodes of the furnace spanned through all five floors, and water based cooling system was used in the facility (CSHIB, 2011). The facility thus had several risk factors including large amount of electricity employed for the EAF, extremely high temperature of operation, generation of explosive gaseous byproducts and potential for toxic CO release (CSHIB, 2011). The explosion led to complete blow out of the furnace, and it could be attributed to damages in refractory lining of the furnace in several regions, as well as unattended water leaks (CSHIB, 2011). The incident that killed two employees in the control room could have been averted if remote monitoring and control system for the furnace was in place, and appropriate leak detection systems as well as gas monitors were installed (CSHIB, 2011). These installations and a proper emergency preparedness plans as well as safe operating procedures need to be developed at Carbide Industries to prevent future incidents. Also all employees in a CO handling facility need to be trained on using appropriate facemasks, respirators and PPE.
References
ATSDR. (2012, June). Toxicological Profile for Carbon Monoxide. Retrieved July 25, 2016,
ATSDR. (2014, May 7). Priority List of Hazardous Substances. Retrieved July 25, 2016,
Bellows, A. (2006, March 29). The Smoldering Ruins of Centralia. Retrieved July 25, 2016,
CDC. (2016). Carbon Monoxide. Retrieved July 25, 2016, from https://www.cdc.gov/niosh/
npg/npgd0105.html
CSHIB. (2011, March 21). Carbide Industries, LLC, Louisville, KY Electric Arc Retrieved
July 25, 2016, from http://www.csb.gov/assets/1/19/Final_Report_small.pdf
EPA. (2016, February 23). Carbon Monoxide | Air & Radiation | US EPA. Retrieved July 25,
2016, from https://www3.epa.gov/airquality/carbonmonoxide/
Newton, D. E. (2016). Carbon Monoxide - Uses. Retrieved July 25, 2016, from http://science.
jrank.org/pages/1213/Carbon-Monoxide-Uses.html
OSHA. (1976, September). Occurpational health guideline for carbon monoxide. Retrieved
July 25, 2016, from http://www.cdc.gov/niosh/docs/81-123/pdfs/0105.pdf
OSHA. (1993, March). Carbon Monoxide In Workplace Atmospheres (Direct-Reading
Monitor). Retrieved July 25, 2016, from https://www.osha.gov/dts/sltc/methods/
inorganic/id209/id209.html
Stracher, G. B. (2007). Geology of coal fires: Case studies from around the world. Retrieved
July 25, 2016, from https://books.google.co.in/books?id=eJU0WOABSWIC&pg=
PA266&lpg=PA266&dq=centralia carbon monoxide&source=bl&ots= v4vCBP8FuH
&sig=amqxB3NZ388bmQ7ZFJH0pqsc6CY&hl=en&sa=X&ved=0ah KEwjry-Pf9Y7OAhUEKo8KHYlnB8QQ6AEIdjAR#v=onepage&q=centralia carbon monoxide&f=false
