Many of the data concerning the combined effects of carbon monoxide and other pollutants found in the ambient air are based on laboratory animal experiments. Only a few human studies are available. Early studies in healthy human subjects on common air pollutants such as carbon monoxide, nitrogen dioxide, ozone or peroxyacetyl nitrate failed to show any interaction from combined exposure.
In laboratory studies, no interaction was observed following combined exposure to carbon monoxide and common ambient air pollutants such as nitrogen dioxide or sulfur dioxide. However, an additive effect was observed following combined exposure to high levels of carbon monoxide and nitric oxide, and a synergistic effect was observed after combined exposure to carbon monoxide and ozone.
Toxicological interactions of combustion products, primarily carbon monoxide, carbon dioxide and hydrogen cyanide, at levels typically produced by indoor and outdoor fires have shown a synergistic effect following carbon monoxide plus carbon dioxide exposure and an additive effect with hydrogen cyanide. Additive effects were also observed when carbon monoxide, hydrogen cyanide and low oxygen were combined; adding carbon dioxide to this combination was synergistic.
Finally, studies suggest that environmental factors such as heat stress and noise may be important determinants of health effects when combined with exposure to carbon monoxide. Besides being a source of carbon monoxide for smokers as well as non-smokers, tobacco smoke is also a source of other chemicals with which environmental carbon monoxide could interact.
Available data strongly suggest that acute and chronic carbon monoxide exposure attributed to tobacco smoke can affect the cardiopulmonary system, but the potential interaction of carbon monoxide with other products of tobacco smoke confounds the results. In addition, it is not clear if incremental increases in carboxyhaemoglobin caused by environmental exposure would actually be additive to chronically elevated carboxyhaemoglobin levels due to tobacco smoke, because some physiological adaptation may take place.
Most information on the health effects of carbon monoxide involves two carefully defined population groups — young, healthy adults and patients with diagnosed coronary artery disease. On the basis of the known effects described, patients with reproducible exercise-induced ischaemia appear to be best established as a sensitive group within the general population that is at increased risk for experiencing health effects of concern i.
Decrements in exercise duration in the healthy population would therefore be of concern mainly to competing athletes, rather than to ordinary people carrying out the common activities of daily life. It can be hypothesized, however, from both clinical and theoretical work and from experimental research on laboratory animals, that certain other groups in the population may be at probable risk from exposure to carbon monoxide.
Identifiable probable risk groups can be categorized by gender differences; by age e. Unfortunately, little empirical evidence is currently available by which to specify health effects associated with ambient or near-ambient carbon monoxide exposures for most of these probable risk groups. Most of this document is concerned with the relatively low concentrations of carbon monoxide that induce effects in humans at, or near, the lower margin of carboxyhaemoglobin detection by current medical technology.
Yet health effects associated with exposure to this pollutant range from the more subtle cardiovascular and neurobehavioural effects at low ambient concentrations to unconsciousness and death after acute exposure to high concentrations of carbon monoxide. The morbidity and mortality resulting from the latter exposures can be a significant public health concern. Carbon monoxide is responsible for a large percentage of the accidental poisonings and deaths reported throughout the world each year. Certain conditions exist in both the indoor and outdoor environments that cause a small percentage of the population to become exposed to dangerous levels of carbon monoxide.
Outdoors, concentrations of carbon monoxide are highest near street intersections, in congested traffic, near exhaust gases from internal combustion engines and from industrial sources, and in poorly ventilated areas such as parking garages and tunnels. Indoors, carbon monoxide concentrations are highest in workplaces or in homes that have faulty or poorly vented combustion appliances or downdrafts or backdrafts. The symptoms and signs of acute carbon monoxide poisoning correlate poorly with the level of carboxyhaemoglobin measured at the time of arrival at the hospital.
Complications occur frequently in carbon monoxide poisoning immediate death, myocardial impairment, hypotension, arrhythmias, pulmonary oedema. Perhaps the most insidious effect of carbon monoxide poisoning is the delayed development of neuropsychiatric impairment within 1—3 weeks and the neurobehavioural consequences, especially in children. Carbon monoxide poisoning during pregnancy results in high risk for the mother, by increasing the short-term complications rate, and for the fetus, by causing fetal death, developmental disorders and cerebral anoxic lesions.
Furthermore, the severity of fatal intoxication cannot be assessed by the maternal rate. Carbon monoxide poisoning occurs frequently, has severe consequences, including immediate death, involves complications and late sequelae and is often overlooked. Efforts in prevention and in public and medical education should be encouraged.
The following guideline values ppm values rounded and periods of time-weighted average exposures have been determined in such a way that the carboxyhaemoglobin level of 2. Carbon monoxide absorbs radiation in the infrared region corresponding to the vibrational excitation of its electronic ground state. It has a low electric dipole moment 0. Property Value Molecular weight Because of the low levels of carbon monoxide in ambient air, methods for its measurement require skilled personnel and sophisticated analytical equipment. A sample introduction system is used, consisting of a sampling probe, an intake manifold, tubing and air movers.
This system is needed to collect the air sample from the atmosphere and to transport it to the analyser without altering the original concentration. It may also be used to introduce known gas concentrations to periodically check the reliability of the analyser output. Construction materials for the sampling probe, intake manifold and tubing should be tested to demonstrate that the test atmosphere composition or concentration is not altered significantly.
Comparative Biology of the Normal Lung
The sample introduction system should be constructed so that it presents no pressure drop to the analyser. At low flow and low concentrations, such operation may require validation. The analyser system consists of the analyser itself and any sample preconditioning components that may be necessary. Sample preconditioning might require a moisture control system to help minimize the false-positive response of the analyser e. The sample preconditioning system may also include a flow metering and flow control device to control the sampling rate to the analyser.
A reference method or equivalent method for air quality measurements is required for acceptance of measurement data. An equivalent method for monitoring carbon monoxide can be so designated when the method is shown to produce results equivalent to those from the approved reference monitoring method based on absorption of infrared radiation from a non-dispersed beam. The designated reference methods are automated, continuous methods utilizing the NDIR technique, which is generally accepted as being the most reliable method for the measurement of carbon monoxide in ambient air.
As of January , no equivalent methods that use a principle other than NDIR have been designated for measuring carbon monoxide in ambient air. Currently, the most commonly used measurement technique is the type of NDIR method referred to as gas filter correlation Acton et al. Carbon monoxide has a characteristic infrared absorption near 4.
The absorption of infrared radiation by the carbon monoxide molecule can therefore be used to measure the concentration of carbon monoxide in the presence of other gases. Most commercially available NDIR analysers incorporate a gas filter to minimize interferences from other gases. They operate at atmospheric pressure, and the most sensitive analysers are able to detect minimum carbon monoxide concentrations of about 0.
Interferences from carbon dioxide and water vapour can be dealt with so as not to affect the data quality.
Services on Demand
NDIR analysers with detectors as designed by Luft are relatively insensitive to flow rate, require no wet chemicals, are sensitive over wide concentration ranges and have short response times. NDIR analysers of the newer gas filter correlation type have overcome zero and span problems and minor problems due to vibrations.
This technique is an automated, semicontinuous method in which carbon monoxide is separated from water, carbon dioxide and hydrocarbons other than methane by a stripper column. Carbon monoxide and methane are then separated on an analytical column, and the carbon monoxide is passed through a catalytic reduction tube, where it is converted to methane. The carbon monoxide converted to methane passes through a flame ionization detector, and the resulting signal is proportional to the concentration of carbon monoxide in the air.
This method has been used throughout the world. It has no known interferences and can be used to measure levels from 0.
These analysers are expensive and require continuous attendance by a highly trained operator to produce valid results. Numerous other analytical schemes have been used to measure carbon monoxide in air. Intermittent samples may be collected in the field and later analysed in the laboratory by the continuous analysing techniques described above. Sample containers may be rigid glass cylinders or stainless steel tanks or non-rigid plastic bags.
Because of location and cost, intermittent sampling may at times be the only practical method for air monitoring. Samples can be taken over a few minutes or accumulated intermittently to obtain, after analysis, either "spot" or "integrated" results. Additional techniques for analysing intermittent samples include colorimetric analysis, in which carbon monoxide reacts in an alkaline solution with the silver salt of p -sulfamoyl-benzoate to form a coloured silver sol; a National Institute of Standards and Technology colorimetric indicating gel incorporating palladium and molybdenum salts , which involves colorimetric comparison with freshly prepared indicating gels exposed to known concentrations of carbon monoxide; a length-of-stain indicator method, which uses an indicator tube containing potassium palladosulfite; and frontal analysis, in which air is passed over an adsorbent until equilibrium is established between the concentration of carbon monoxide in the air and the concentration of carbon monoxide on the adsorbent.
A simple and inexpensive measurement technique uses detector tubes indicator tubes Leichnitz, This method is widely applied in industrial hygiene and is suitable for analysis of highly polluted atmospheric air. The iodine-coloured layer in the tube corresponds in length to the carbon monoxide concentration in the sample.
- Mathematical Intuition: Phenomenology and Mathematical Knowledge.
- Healthy human aging: intrinsic and environmental factors;
- StarGuides Plus: A World-Wide Directory of Organizations in Astronomy and Related Space Sciences;
- Managing Cooperation in Supply Network Structures and Small or Medium-sized Enterprises: Main Criteria and Tools for Managers.
- Degradation Rate of Bioresorbable Materials: Prediction and Evaluation.
- The Lung 2E.
- Seamless Crochet: Techniques and Motifs for Join-As-You-Go Designs?
Until the s, most of the data available on ambient carbon monoxide concentrations came from fixed monitoring stations operated routinely in urban areas. The accepted measurement technique was NDIR spectrometry, but the instruments were large and cumbersome, often requiring vibration-free, air-conditioned enclosures.
Without a portable, convenient monitor for carbon monoxide, it was extremely difficult to measure carbon monoxide concentrations accurately in the microenvironments that people usually visited. Carbon monoxide detectors have been designed like residential smoke detectors — to be low cost, yet provide protection from a catastrophic event by sounding an audible alarm. The carbon monoxide detector industry is young, however, and is in a stage of rapid growth. In the USA, an estimated 7—8 million detectors have been purchased since the early s, but the numbers used in homes will continue to rise as local municipalities change building codes to require the installation of carbon monoxide detectors in new residential structures containing combustion-source appliances, stoves or fireplaces.
Currently available carbon monoxide detectors are based on an interactive-type sensor e. They are battery-powered, alternating current-powered or both. The most popular alternating current-powered detectors have a heated metallic sensor that reacts with carbon monoxide; the battery-powered detectors have a chemically treated gel disk that darkens with exposure to carbon monoxide or a fuel cell.
Small, inexpensive carbon monoxide detection cards or tablets that require frequent visual inspection of colour changes do not sound an alarm and are not recommended as a primary detector. Carbon monoxide detectors are sensitive to location and environmental conditions, including temperature, relative humidity and the presence of other interfering gases.
Carbon Monoxide (Second edition) (EHC , )
They may also become less stable with time. For example, they should not be installed in dead-space air i. Excessive heat or cold will affect performance, and humidity extremes will affect the activation time. Utilization of non-interactive infrared technology e. In the USA, a new voluntary standard for carbon monoxide detectors was published in by the Underwriters Laboratories UL Standard and revised in This standard provides alarm requirements for detectors that are based on both the carbon monoxide concentration and the exposure time.
Approximately 15 manufacturers produce detectors listed under UL Standard Because UL Standard covers a wide range of exposure conditions, there has been some ambiguity about its interpretation. In fact, alarm sensitivities are still a problem for the industry, and further discussion and direction are needed. Thus, current detectors provide warning against carbon monoxide levels that are protective of the healthy population only. Despite these limitations, carbon monoxide detectors are reliable and effective, continue to improve and should be recommended for use in homes in addition to smoke detectors and fire alarms.
A unique feature of carbon monoxide exposure is that there is a biological marker of the dose that the individual has received: the level of carbon monoxide in the blood. This level may be calculated by measuring carboxyhaemoglobin in blood or carbon monoxide in exhaled breath. The level of dissolved carbon monoxide in blood is normally below the level of detection but may be of importance in the transportation of carbon monoxide between cells and tissues see chapter 6.
Thus, the blood level of carbon monoxide is conventionally represented as a percentage of the total haemoglobin available i.
Related The Lung, Second Edition: Development, Aging and the Environment
Copyright 2019 - All Right Reserved