|
|
PORTABLE INSTRUMENTS Select next to see Products | [BACK] [NEXT] |
|
Single-Gas Monitors for Combustible Gases
Single-gas instruments for monitoring combustible gases and vapors are generally calibrated on pentane and are designed for general-purpose monitoring of hydrocarbon vapors. Such instruments operate by the catalytic action of a heated platinum filament in contact with combustible gases (see Figure 5).The filament is heated to operating temperature by an electric current. When the gas sample contacts the heated filament, combustion on its surface raises the temperature in proportion to the quantityof combustibles in the sample. A Wheatstone bridge circuit, incorporating the filament as one arm, measures the change in electrical resistance due to the temperature increases. This change indicates the percentage of combustible gas present in the sample. Single-Gas Monitors for Toxic Gases Compact, battery-powered devices can be used to measure levels of such gases as carbon monoxide (CO) or hydrogen sulfide (H 2S), depending on the model selected. Toxic gas monitors use electrochemical cells (see Figure 6).If the gas of interest enters the cell, the reaction produces a current output proportional to the amount of gas in the sample. With these instruments, audible and visible alarms sound if the gas concentration exceeds a preset level. These devices are well suited for use in confined spaces containing motorsor engines, which can generate large quantities of CO, as well as in sewers, waste treatment plants and "sour crude" processing stations which tend to have hazardous volumes of H 2S.
|
|
Multiple-Gas Monitors for Oxygen andCombustible Gas In applications where it is necessary to determine oxygen and combustible gas levels simultaneously, 2-in-1 diffusion-type devices can be used. Sensors measure 0 to 100 percent of the LEL and oxygen from 0 to 25 percent. Remote sampling requires either a pump module or an aspirator bulb adapter.Multiple-Gas Monitors for Oxygen, Combustible and Toxic Gases Toxic gases and vapors, which can be inhaled or absorbed through the skin, are frequently found in confined spaces. Sometimes, these atmospheric hazards can also displace oxygen and may incapacitate the body’s ability to maintain respiration. Some toxic gases and vapors can also cause longterm physical damage to the body in cases of repeated exposure. A number of instruments are available to assist in detecting toxic gas. Pocket-size monitors operate by diffusion or an aspirator bulb. Larger instruments with built-in pumps draw samples from the immediate area or from outside the confined space work area when used with sampling lines. Diffusion-type instruments are available for simultaneously measuring the LEL of combustible gases, oxygen levels and toxic levels (in parts per million) of H 2S,CO and other toxic gases. Alarms also alert the user to low and high oxygen levels. Remote sampling pump adapters are available to convert these diffusion-type instruments into pump-style instruments.
Photoionization Devices for Toxic Gases and Vapors A photoionization detector, featuring microprocessor technology, uses ultraviolet light to ionize molecules of chemical substances in a gaseous or vaporous state (see Figure 7).A real-time digital readout allows the user to make an immediate determination of gas and vapor concentrations. Depending upon calibration input, gas and vapors are measured over a 0.1 to 10,000 ppm scale.Some instrumentsautomatically compensate for signal loss due to humidity, which is inherent in all PID detectors.
|
|
Detector Tube Sampling Systems Detector tube-type devices are recommended for conducting quick evaluations of potential hazards that cannot otherwise be measured. With detector tubes, a known volume of air is drawn through the tube, using a manually operated or battery-powered sampling pump. If gas or vapor is present in the air, chemically treated granules in the tube are stained a different color. By measuring the length of the color stain within the tube, users can determine concentration levels. Most tubes available today are made of glass, have break-off tips, and are filled with treated chemical granules. They generally have a shelf life of 24 to 30 months. One type of pump frequently used with a detector tube is a compact, bellows-type device.Accurate and repeatable sample flows can be assured by a shaft that guides the bellows during compression. Some models feature an end-of stroke indicator that lets the user know when a full air sample has been drawn. Models with an integral stroke counter eliminate the tedious recording of multiple pump strokes. Personal Sampling Personal sampling is used to determine the concentration of airborne contaminants. Personal sampling pumps are designed to measure individual workers’exposures, so they typically are lightweight, belt-mounted, battery-powered devices. The process of sampling entails drawing a predetermined volume of air through a filter designed to trap contaminants. The filter is contained in a plastic cassette, which is attached by plastic tubing to a sampling pump calibrated to draw a specific, known volume of air into the filter .After air samples are drawn, the filters are sent to a laboratory where they are examined to determine the level of exposure. Personal sampling determines the concentration found in the "breathing zone "or the area near the worker’s face, which is usually measured at or near the collar or lapel. Calibration To ensure the accuracy of all monitoring and detection equipment, calibration should be performed regularly. If the instrument reading differs significantly from the values of the known standard, the instrument should not be used until it has been adjusted or, if necessary, repaired.
CALL SUPER SAFETY FOR YOUR AIRMONITORING NEEDS TALK TO AN INDUSTRIAL HYGIENIST(800) 275-8239 |
|
Fax: (773) 538-8080 |
Telephone: (800) 275-8239 |
Website: www.supersafety.com |
page 67 |
|---|
