Chua
please help me...
i need it for my report..
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.i need the gadgets whoch are really rare...
Answer
CO (poison) detectors - should be in every house in case furnace has issues
Sensors
Early designs were basically a white pad which would fade to a brownish or blackish colour if carbon monoxide were present. Such chemical detectors are cheap and widely available, but only give a visual warning of a problem. As carbon monoxide related deaths increased during the 1990s, audible alarms became standard.
The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations (eg 100 parts per million) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to relatively common sources of carbon monoxide such as cigarette smoke.
There are four types of sensors available and they vary in cost, accuracy and speed of response.[10] The latter three types include sensor elements that typically last up to 10 years. At least one CO detector is available which includes a battery and sensor in a replaceable module. Most CO detectors do not have replaceable sensors.
[edit]Opto-Chemical
The detector consists of a pad of a coloured chemical which changes colour upon reaction with carbon monoxide. They only provide a qualitative warning of the gas however. The main advantage of these detectors is that they are the lowest cost, but the downside is that they also offer the lowest level of protection.
[edit]Biomimetic
A biomimetic (chem-optical or gel cell) sensor works with a form of synthetic hemoglobin which darkens in the presence of CO, and lightens without it. This can either be seen directly or connected to a light sensor and alarm. Battery lifespan usually lasts 2-3 years. Device lasts on the average of about 10 years. These products were the first to enter the mass market but have now largely fallen out of favour.
[edit]Electrochemical
This is a type of fuel cell that instead of being designed to produce power, is designed to produce a current that is precisely related to the amount of the target gas (in this case carbon monoxide) in the atmosphere. Measurement of the current gives a measure of the concentration of carbon monoxide in the atmosphere. Essentially the electrochemical cell consists of a container, 2 electrodes, connection wires and an electrolyte - typically sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon dioxide while oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over other technologies in that it has a highly accurate and linear output to carbon monoxide concentration, requires minimal power as it is operated at room temperature, and has a long lifetime (typically commercial available cells now have lifetimes of 5 years or greater). Until recently, the cost of these cells and concerns about their long term reliability had limited uptake of this technology in the marketplace, although these concerns are now largely overcome. This technology is now the dominant technology in USA and Europe.
[edit]Semiconductor
Thin wires of the semiconductor tin dioxide on an insulating ceramic base provide a sensor monitored by an integrated circuit. This sensing element needs to be heated to approximately 400 deg C in order to operate. Oxygen increases resistance of the tin dioxide, but carbon monoxide reduces resistance therefore by measurement of the resistance of the sensing element means a monitor can be made to trigger an alarm. The power demands of this sensor means that these devices can only be mains powered although a pulsed sensor is now available that has a limited lifetime (months) as a battery powered detector. Device usually lasts on the average of 5-10 years. This technology has traditionally found high utility in Japan and the far east with some market penetration in USA. However the superior performance of electrochemical cell technology is beginning to displace this technology
Is it safe to use a natural gas oven to heat a house?
funkybass4
are the fumes dangerous?
Answer
no
Carbon monoxide is a lot like an elusive criminal -- it's highly dangerous and you can't see or smell it. In fact, it's often called "the silent killer."
You can protect your family from the dangers of this deadly gas by taking preventive measures and by learning to recognize the symptoms of carbon monoxide poisoning.
Check out the following safety tips to keep your home safe from the build up of dangerous carbon monoxide. If you need more information about carbon monoxide poisoning and prevention, call the Poison Control Center at 1-800-POISON-1 (1-800-764-7661).
Traditionally, few people have considered gas ovens to be a major source of carbon monoxide (CO), even though all their exhaust products are often vented directly into the indoor air of a residence. Yet unvented space heaters with a similar output of combustion gases have been banned in many states because of indoor air quality (IAQ) dangers inherent in their use.
CO poisoning in homes is generally the most serious of the wide variety of IAQ problems, in that people can die quickly from it, whereas most other such problems can be considered chronic. Weatherization personnel must perform a variety of combustion safety tests to determine if CO is being produced by any of the combustion appliances in a residence. If they find dangerously high levels, the crew should know how to fix the problem.
CO and Its Effects
Carbon monoxide is a colorless, odorless, nonirritating, but highly toxic, gas. It is flammable and slightly lighter than air. It is produced whenever there is incomplete combustion of hydrocarbon fuels--that is, when there is insufficient air to burn the fuel completely. The highest concentrations of CO typically occur at start-up of the appliance. This is especially true of ovens, because little or no air can flow through the oven until the air inside it heats and rises out of the exhaust vent.
High levels of CO cause headaches, nausea, shortness of breath, dizziness, confusion, brain damage, and, in severe cases, death. CO strangles the victim by reducing the amount of oxygen that can get to cells and impairing the body's usage of oxygen even if it reaches the cellular level. Victims should be removed from the exposure, though symptoms often persist well after removal from the source. That is because the so-called half life of CO in blood--the time for the peak concentration to decline to half its original value--is about four hours.
Often the symptoms are similar to those of flu. People who may have been exposed to CO should go to the hospital for a simple blood test. Another option is to check carboxyhemoglobin levels in the blood using a breath CO detector. A relatively inexpensive ($95) attachment is now available for Bacharach MONOXOR II carbon monoxide monitors, which are widely used for combustion safety testing.
Symptoms are related to the exposure level and time of exposure. The U.S. Environmental Protection Agency (EPA) recommends that a person should not breathe CO concentrations of 9 parts per million (ppm) or higher for any eight-hour period; 35 ppm or higher for any one-hour period; or 200 ppm or higher at any one time. Moreover, a person should not be exposed to any one of these three conditions more than once per year. The World Health Organization and Health Canada recommend a maximum exposure of 25 ppm for a one-hour period. ASHRAE Standard 62-1989 recommends an exposure limit of no more than 9 ppm in a living space, and Japan has an indoor standard that limits exposure to 10 ppm for any duration.
Recommended Oven CO Test Protocol
All gas and propane ovens should be tested for combustion safety, since they can be a major source of carbon monoxide (CO).
Test the oven in its as-found condition (do not clean or adjust) before starting any weatherization.
Use an electronic CO meter with a range of 0 ppm-2,000 ppm and a resolution of 1 ppm, such as the Bacharach MONOXOR II. Older nonelectronic meters or diffusion tubes are not suitable.
Zero the CO meter. This is typically done outdoors in a rural or unpolluted area. Do not rezero for individual houses. Calibrate the meter with 10 ppm and 500 ppm calibration gas about every six months (check zero at this time).
Turn the kitchen exhaust hood on, if one exists, to avoid exposing test personnel to potential CO.
Insert the CO meter probe tip well into the oven exhaust vent (typically an opening about 1 in high by 5 in wide centered in the back dial section on the top of the stove). The intent is to monitor the exhaust gases inside the oven exhaust before they are outside the oven and diluted with air.
Turn the meter on and then turn the oven on bake at 350deg.F with the oven door closed.
Watch the CO meter reading rise and record the peak or maximum reading. It should typically reach a peak within about 5 to 10 minutes and then begin to drop back down again to a steady value after a much longer time.
If the peak value is less than 100 ppm, the oven is not producing elevated levels of CO and need not be tuned or adjusted. Weatherization can continue.
If the peak value is greater than 100 ppm, turn the oven off. It is producing elevated levels of CO that could cause adverse health effects. It needs to be cleaned, tuned, or otherwise adjusted prior to or in conjunction with any air tightening of the dwelling.
If aluminum foil is lining the oven bottom, it needs to be removed or perforated along its edges so the secondary air holes in the oven bottom are not blocked. Such blockage is a major cause of high CO levels.
If the CO levels are still above 100 ppm after removing or fixing the foil, or if no foil is present, clean or tune the oven.
After the oven has completely cooled (at least 30 minutes with the oven off and the oven door open), turn the oven back on. Recheck the peak CO level in the oven exhaust gases.
Continue to adjust and recheck the peak exhaust CO level until it is below 100 ppm; only then continue with weatherization. Almost all ovens can be satisfactorily tuned in the field.
If, after repeated tuning attempts, the CO levels are still elevated, call the oven manufacturer. A few models cannot be satisfactorily tuned.
If the occupants complain of headaches, nausea, flulike symptoms, or worse, or if a home CO detector alarm has gone off recently, measure the occupants' CO blood levels with a breathalizer or recommend that the occupants get a blood test immediately at a hospital. Turn off all combustion appliances.
In extreme cases, it may be advisable to measure the maximum steady CO level in the kitchen air. After oven start-up it typically takes at least an hour to reach that level in loose dwellings and may take upwards of 8 to10 hours in very tight homes.
Consider giving any client whose dwelling has any type of CO combustion appliance, or at least those whose oven was not satisfactory, a home CO detector. Types with an LED readout are preferable (see "Conservation Clips: CO Detectors Not Created Equal" p. 63).
Two important caveats:
(1) This protocol does not apply to convection ovens, which have been known to blow hot air full of CO into the auditor's face. (2) A separate protocol needs to be developed for testing stove burners. In both cases, the indoor CO level should be tested.
Field Test Findings
Excessive carbon monoxide production from combustion appliances and CO poisoning are much more common than has previously been recognized. Among 25 homes with gas ovens tested in an ongoing survey by Montana Power Company's Low-Income Weatherization Program in Kalispell, Montana, CO concentration in the kitchen was found to be greater than 9 ppm in the cooking area in every case.
At Portland State University (PSU), my group measured IAQ in 23 low-income homes. One-third had ovens that caused levels in the cooking area to exceed the eight-hour 9 ppm standard after 20 minutes. However, 10 of the 23 cases showed CO levels increasing with time. (CO levels from the oven operation were monitored at 3, 10, and 20 minutes after turning on the oven.) That indicated the need to go back and continue testing over a longer time period. Most of the apartments or homes were fairly small and apparently leaky, demonstrating that leaky dwellings, as well as tight ones, are vulnerable.
In the few cases where CO released from stoves has been monitored, the stoves probably were not left on long enough to reach the maximum CO levels in the kitchen air. We conducted a follow-up study in Portland to determine just how long it takes to reach steady-state conditions (maximum indoor CO levels). Sixty ovens were monitored in two relatively leaky apartment buildings with the oven set on broil and the oven door closed. Half of the readings were over 9 ppm, and 15% were over the one-hour 35 ppm standard level.
The minimum time for an oven to reach maximum CO levels in the surrounding air was 20 minutes, but the average was 45 minutes to 60 minutes. Reaching equilibrium in that short a time implies that the apartments were very leaky, as was the case. Had they been much more airtight, it could have taken many hours to reach steady-state conditions, though the steady-state level would be higher than that in the leakier units. Tight homes also tend to have higher indoor CO levels from long-term oven operation.
The study also found that CO levels in the exhaust ports can indicate potential IAQ problems. In the field tests, about 40% of the ovens had CO production levels in excess of 50 ppm in their undiluted exhaust port at the time of the maximum CO reading in the kitchen air; the highest reading was over 2,000 ppm, and the average was 100 ppm. Ovens should be tuned if the steady-state CO levels in their undiluted exhaust gases is above about 25 ppm. Higher exhaust concentrations can produce indoor air readings above 9 ppm, with consequent adverse health effects.
Other field tests have corroborated the studies in Montana and Oregon. One low-income home I tested in Philadelphia had a CO level of 330 ppm in the kitchen air after only five minutes of oven operation! Similar problems were found with hundreds of homes in a study directed by Bruce Davis as part of low-income weatherization efforts in Arkansas. In almost every case the excess CO levels in the oven exhaust ports were reduced to below about 25 ppm after the oven was cleaned or adjusted.
It is particularly important to recognize that gas ovens are used as either the main or a supplemental space heating source in numerous U.S. homes, especially low-income homes. Two medical studies have indicated that 40%-50% of all urban low-income dwellings are heated with their ranges. It would seem reasonable that a similarly large fraction of nonurban low-income dwellings are heated in the same way. Given that about half of the ranges in the United States are gas or propane fired, and that about 20% of the U.S. population is classified as low-income, the potential problem is enormous.
The evidence suggests as much. In a recent study of the factors setting off CO detector alarms after their use was mandated in Chicago, stoves (either stove burners or ovens) were deemed responsible in 78% of the cases. At one Kentucky hospital, when patients coming into the emergency room with flulike symptoms were given blood tests, about 25% were found to have CO poisoning. These limited test results indicate that combustion appliance operation is often unacceptable. Monitoring for safety should be the first priority for weatherization crews.
Oven Repair
There is very little information readily available on how to adjust, clean, or otherwise tune an oven that is producing excessive levels of CO. However, experience in Arkansas with more than 300 ovens and in a PSU research project indicates that the following items should be checked:
Primary air adjustment--check the shutter opening. This is very important.
Fuel orifice size. The size will be different for liquified petroleum (LP) and natural gas.
Oven supply pressure. It is usually best to maintain the value stamped on the plate--usually 3.5-4.5 in of water (870-1,100 Pa) for natural gas and 9-11 in (2,200-2,700 Pa) for LP. Also check rated heat input on the plate and ensure that the orifice and pressure combination provides that input.
Secondary air path. Secondary air holes should be cleaned or cleared; pay special attention to the presence of aluminum foil lining the bottom of the oven and covering the secondary air holes.
Burner and pilot. These should be cleaned.
The good news is that most ovens can easily be repaired so that they emit little or no CO in the exhaust port, typically below 100 ppm peak or 25 ppm steady state. Ovens are basically simple devices, and repair tools cost little. A Dwyer, Ritchie, Bacharach, or other brand U-tube manometer to measure the gas pressure should cost between $10 and $40. A small brass wire brush, flair wrenches, and an asbestos glove are used for tuning as well.
Kitchen Exhaust Fans
Ventilating combustion products directly out of the kitchen eliminates the opportunity for them to affect occupants. This would get rid of CO and also oxides of nitrogen that are always present. These pollutants are a special concern in tight houses.
Kitchen fans are generally noisy, in part because they have relatively high flow rates. If they are too noisy, people will be reluctant to use them. Thus in selecting an exhaust fan to install in an existing home, look for one that is relatively quiet. It may require a fan with a somewhat lower capacity, but that is probably a good tradeoff. It's better to have a lower-power fan that is used than a high-power one that isn't. One fairly quiet option for retrofitting a fan into an existing home is remote installation: an axial fan that is rated for greasy air can be installed in an attic.
Finally, it is important to educate clients about the need to use their kitchen exhaust fan (if one exists) whenever the range is operating. Often people think that the only reason to use it is to get rid of cooking odors. Using fans can help reduce indoor pollutant concentrations by removing the pollutants at their source.
Whether or not an exhaust fan exists, safety tests should be performed in any home with combustion appliances, particularly before any weatherization efforts are undertaken. These simple tests have the potential to eliminate a serious safety problem.
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