May 14, 2008

Gas applications

1. Vehicle exhaust


2. Waste water treatment


3. Pulp & paper


4. Battery rooms


5. Brewing & bottling


6. Human occupancy detection


7. Indoor air quality


8. Landfill sites


9. Refrigerants


10. Ammonia monitoring


11. Mining and mineral processing

1. Vehicle exhaust
Vehicle exhaust presents an interesting challenge when designing a gas detection system. Because of the wide variety of applications including underground parking garages, bus barns, maintenance facilities, tunnels, train stations, airports, loading docks, car and truck dealerships and warehouses, a number of different solutions exist to satisfy the varying requirements. Therefore, a number of factors must be taken into consideration when determining what type of system should be specified.

1. Size of space to be monitored: For most vehicle exhaust applications, systems are designed to have one sensor per 7000 square feet. In larger, wide-open spaces, where air is free to move freely, this can be expanded to 9000 square feet. In areas comprised of dividers, sections, corners and other barriers to free movement of air, this should be condensed to one sensor per 5000 square feet.



2. Number of areas or zones: If an area is to be partitioned into distinct areas for the purpose of ventilation, alarming, or other control functions, sensors can be lumped together in a per zone basis.



3. Visual Indication: Does the user require a real-time concentration readout, per sensor alarm indication (at the panel or sensor location) or will common alarm indication be sufficient.



4. Output requirement: Are alarm contacts required, or will the user be providing his/her own control functions, therefore requiring only sensor/transmitters with analog (4-20 mA) output.



5. Type of fuels being used: If vehicles being monitored are gasoline, propane or natural gas powered only, then CO monitoring is sufficient. If however, diesel vehicles are being used, nitrogen dioxide (NO2) sensors should be used as well.



6. Type of vehicles in use: In diesel applications, the type of vehicle is relevant to sensor placement. In instances in which large trucks with vertical exhaust stacks are prevalent, NO2 sensors should be mounted near the ceiling, as the exhaust will collect at the ceiling before slowly descending as it cools. In circumstances where fumes are exhausted near the ground as per a standard car or pick-up truck, sensors should be mounted at or about breathing level.



7. Potential interference gases: For areas such as maintenance garages or other spaces in which chemicals such a s gasoline, varsol, ammonia, paint, or other solvents may be present, care should be taken to use electrochemical CO sensors in order to avoid false alarms resulting from interference gases. In areas such as parking garages, solid-state sensors should be sufficient.



8. Desired sequence of operations: The required sequence of operations for activation of auxiliary equipment must be taken into consideration when specifying systems. Are individual sensors to initiate particular operations, therefore requiring individual relay outputs, or will multiple sensors initiate single operations, therefore requiring only single, common relay outputs.



9. Auxiliary equipment: Care must be taken to ensure adequate control functions for all auxiliary equipment including ventilation, audible and visual alarms, and remote annunciation.

Once these factors have been determined, a selection of the most appropriate AMC system must follow. Here is a basic outline of different AMC exhaust monitoring systems, and when and where they should be used.

Single/dual sensor systems

AMC 1ACO : This is a basic monitor with a single, integral, electrochemical sensor. It comes complete with relay contacts, LED alarm indication and audio alarm. Ideal as a stand-alone in small parking facility applications.

AMC 1AVC : This system is a two-channel version of the AMC 1ACO, which incorporates BOTH integral, electrochemical CO and NO2 sensors, with common alarm outputs and optional concentration readouts.

Multiple sensor systems

AMC 1A22-TT-X: This system will provide LED indication and relay contact outputs on a per sensor basis. Can be used for up to two remote sensor/transmitters (one per channel). Suited for use in applications requiring a complex sequence of operations and ventilation equipment activation. Sensors are wired individually back to the panel.

AMC 1AD Series : The AMC 1AD-Series is an economical system designed to provide alarm indication and relay activation on a zoned basis, with up to eight sensor modules (AMC 1220 Series), wired in series back to each of two zones. Designed for use in applications featuring simple sequences of operations (any of the sensor alarm will activate all of the fans, within a zone). All sensors within each zone are wired in a daisy-chain manner, back to the panel.

Sensors and sensor/transmitters

AMC 2751: Electrochemical, 4-20 mA CO sensor/transmitter, for use with all panels (exception AMC 1AD Series). Individually wired to AMC panel or clients building management system.

AMC 1220 Series : For use exclusively with the AMC 1AD Series, the AMC 1220 Series or AMC 1222 Dual Sensor module can be wired in flexible configurations for the most economical system in multi-sensor applications.

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2. Waste water treatment
Growing environmental concerns have resulted in the construction and upgrading of wastewater treatment plants throughout North America.

By their very design, processes involved in sewage treatment produce and use a number of highly toxic and explosive gases requiring monitoring to ensure the safety of both employees and the environment.

There are three main gases to be aware of when designing monitoring systems for wastewater treatment facilities.

Methane: Also known as natural gas, methane is an explosive gas (L.E.L 5% volume) produced primarily in the initial stages of decomposition. Because of its low density, methane will accumulate in pockets near the ceiling of enclosed areas such as holding tanks and settling basins.

Oxygen: Because of the high number of chemical and organic processes occurring in any wastewater treatment plant, adequate levels of oxygen must be maintained to ensure worker safety. Oxygen sensors should be located in enclosed areas, wherever oxygen levels may be in question.

Purifying chemicals: Chemicals such as ammonia, ozone and chlorine are all used in the decontamination of water, both in wastewater and water purification plants.

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3. Pulp & paper
Pulp and paper mills present many dangerous situations, which can be significantly decreased by utilizing continuous gas monitoring.

The chemical pulping technique in the Kraft process utilizes a combination of heat and liquor (chemicals) to delignify wood and reduce it to pulp. Reduction of the wood to pulp takes place in stages, but the heart of the process is in either batch or continuous digesters. It is here that hazardous gases such as hydrogen sulfide and mercaptan are released due to the chemical reaction between the wood chips and liquors.

Pulp stock from the digesters is washed and screened and then sent through the bleaching process. Bleaching is associated with whiteness or brightness, as it is referred to in the pulp and paper industry.

Normally it consists of an oxidation process, wherein oxygen is used to dissolve unwanted colored components. In pulp bleaching, oxidation is used to break down lignin molecules, but also to bleach out the dark spots created by non-cellulose components of wood, such as resins, or foreign matter in the pulping process. Brightness is also obtained by dissolving the lignin molecule through chlorinating. Its removal makes the remaining cellulose fibers appear white to the eye. Bleach chemicals used in this process are chlorine, chlorine dioxide most frequently, oxygen, peroxide and ozone used as alternatives. Sulfur dioxide is also a concern in the primary bleaching process.

In Kraft mills, the chemicals used are recycled for use throughout the mill. The recovery process is integrally connected to the boilers and power production. All chemicals are recovered through the burning of black liquor (liquor which has already been through the digestive process) in the recovery boiler. Heat released by the oxidation of liquor is used to produce steam for use throughout the plant. Monitoring of hydrogen sulfide gas using the, should be a priority in these locations.

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4. Battery rooms
As lead acid batteries are charged, minute quantities of hydrogen (H2) gas are produced. Normally, the amount of hydrogen generated during charging is not of a sufficient quantity to cause concern. There are instances however, where for various reasons; hydrogen may accumulate to cause potentially hazardous conditions.

Battery back-up installations for equipment such as telephone switching systems and computers are normally situated in small rooms with little ventilation. This confined space provides an excellent opportunity for hydrogen to accumulate and reach combustible levels.

In most instances, the sensor/transmitter is mounted on the ceiling, while the monitoring panel is mounted outside the room. Any build-up will cause an alarm and/or initiate ventilation.

A second common application is in warehouses where battery powered forklifts are used. Charging stations are commonly lined up in areas where a large number of vehicles can be charged simultaneously.

Because of the size and number of batteries, dangerous levels of H2 can accumulate.

Key Factors:

• Relative density of hydrogen is 0.069. Therefore sensors should be mounted at or near the ceiling, away from any source of fresh air, which may dilute the sample.



• Remote sensors are normally used, with panels being mounted away from hydrogen source.

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5. Brewing & bottling
Carbon dioxide is a by-product of the fermentation process, as well as a raw material used in carbonation. Carbon dioxide leaks could result in over exposure to employees, as well as possible product damage.

Ammonia and other refrigerants are commonly monitored to detect for leaks in chillers and refrigeration systems. For more detailed information regarding refrigeration gas detection please see our refrigeration application sheet.

Warehouse forklifts powered by propane or liquefied natural gas have a two-fold hazard, in that leaks of these products can prove catastrophic because of their explosive nature and, toxic carbon monoxide is an exhaust by-product of these machines and if not properly ventilated, it can prove deadly. Nitrogen dioxide is often monitored in areas where diesel trucks are present. For more information on vehicle exhaust, see our vehicle exhaust application sheet.

Forklifts powered by electricity may also prove hazardous due to the highly explosive hydrogen given off when batteries are recharging. For more information on vehicle exhaust, see our battery room application sheet.

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6. Human occupancy detection
All around the world there are many organizations and companies that have a need for a portable and effective system to detect stowaways, escapees, spies, or anyone hidden inside any crate or container.

1. Air, sea, and ground transportation


2. Border crossings


3. Correctional facilities


4. Military bases

For organizations involved in cross border shipments, stowaways can present an increasingly costly problem. Under current law, carriers often become liable for a fine, plus the stowaway’s housing, food, healthcare, supervision, legal representation and repatriation costs.

This has led the Armstrong Monitoring Corporation to develop an easy-to-use portable carbon dioxide detection system designed to check for human occupancy. By monitoring for elevated carbon dioxide levels in shipping containers, a reliable indication of human occupancy is given, allowing early detection.

Time is money, and when terminals are loading two or three containers per minute, a portable system permits quick and easy testing, realizing savings in both the long and short term.

AMC CD-2 field operation

The Armstrong Monitoring CD-2 Human Occupancy Detector (HOD) has been developed to detect the presence of humans in confined spaces i.e. shipping containers, enclosed rail cars, tractor trailers, automobiles, etc. It has been used with great success by immigration authorities throughout Canada and Europe to detect unauthorized personnel attempting to cross international borders illegally.

When sampling, a substantial increase of two to three times clean air is required to indicated human occupancy. The following two examples will demonstrate this principle:

1. A baseline of 400 parts per million (PPM) is recorded in outside air. After taking a sample from within an enclosed boxcar, the reading increases to 550 PPM. This minimal increase would not indicate a likelihood of human occupation.



2. A baseline of 350 PPM is recorded. A reading from inside a tractor trailer indicates 1100 PPM. This should alert personnel to the likelihood of unauthorized personnel and steps should be taken to investigate further.

It must be remembered that human respiration is not the only process, which will produce carbon dioxide. The following are other possible sources of unusually high readings:

1. Livestock: Any animals breathing will produce carbon dioxide.



2. Fermentation: If rotting organic material has begun to ferment, elevated levels will be witnessed.



3. Packaged carbon dioxide: Products such as soda contain carbon dioxide. Breakage of containers will result in elevated levels.

The AMC CD-2 will be effective only when samples are taken from relatively confined spaces. A railcar with perforated or louvered walls i.e. an automobile carrying car, will not allow carbon dioxide levels to increase to a discernable level before being ventilated. If however, small vents are present which allow only limited fresh air, and indicative reading can be taken.

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7. Indoor air quality
Contemporary HVAC systems usually provide a fixed quantity of fresh air to a building, based on the maximum number of people expected to occupy the space.

When occupancy is below the design maximum, fresh air intake can be reduced, thereby decreasing energy consumption for heating and/or cooling of incoming outside air. Because carbon dioxide concentrations are a direct function of the number of people occupying a space, the monitoring of CO2 is an ideal indicator to control the level of ventilation.

A perfect example of this principle is in the case of a movie theatre. For long periods of time, it is virtually empty. As the theatre begins to fill, carbon dioxide levels will gradually rise. By monitoring this increase, and increasing fresh air intake accordingly, air quality can be maintained with minimum ventilation and corresponding minimum expense. When the movie ends, people file out quite rapidly, resulting in an abrupt decrease in CO2 production, thereby returning ventilation requirements to a minimum.

The same principle can be used in any building, becoming more cost effective the more occupancy varies. This would include many commercial and institutional buildings which remain unoccupied overnight and on weekends.

Two basic configurations are available when designing a ventilation system utilizing carbon dioxide monitoring. Either sensors are located throughout the space, giving readings in a number of key areas and allowing ventilation to be directed to specific areas requiring fresh air; or sensors are placed in the return air duct, giving an indication of overall building requirements.

The deciding factor in configuration choice would be the air distribution system of the particular building.

Attempts have been made to use other parameters to regulate ventilation. Oxygen levels have too great a "normal" fluctuation range to be of practical use. Humidity has been used, but because of its dependence on other factors such as outdoor humidity and indoor activity (cooking, showers, etc.) it too cannot be counted on as an accurate indicator of air quality. Carbon monoxide has been used quite successfully in smoking areas, but in normal indoor air, CO levels vary little with occupancy.

Other contaminants which may contribute to poor air quality, may not be accounted for by monitoring CO2 level alone. Formaldehyde, oxides of nitrogen, carbon monoxide and radon may be present regardless of occupancy. Hazardous fumes from cigarette smoke will also adversely affect air quality.

If these factors are taken into consideration, carbon dioxide monitoring can be a key component of your energy efficient HVAC system.

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8. Landfill sites
The permeation of ground-based methane presents a concern when looking at structures built on former or existing landfill sites.

As waste materials from the landfill sites degrade, one of the by-products is highly combustible methane gas. As methane is less dense than air, it constantly rises to the surface. If gas becomes trapped in basements or other enclosed areas, a potentially catastrophic situation can occur.

By installing combustible gas detection equipment, disaster may be avoided by initiating ventilation and/or notifying inhabitants of the hazard before it becomes critical.

Whether simply to alarm, or to initiate ventilation, standard Armstrong equipment can satisfy the requirements.

Storage and maintenance garages for heavy equipment such as bulldozers and dump trucks have a need to monitor exhaust fumes. Within these enclosed areas high levels of carbon monoxide and nitrogen dioxide (diesel exhaust) can accumulate quickly and pose a threat to employees. For more information on CO and NO2, see our vehicle exhaust application sheet.

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9. Refrigerants
In this world of new-found environmental consciousness, refrigerant gases have come under attack as a prime villain.

Chlorofluorocarbons, commonly known as CFCs, which were formerly considered relatively safe, are now known to be a key contributor to the thinning of the ozone layer.

These are gradually being replaced by more environmentally friendly refrigerants such as R134a. This however, does not lessen the need for leak detection.

In most applications, solid state sensing technology will provide economical leak detection for most refrigerants. If however, there are other gases in the background in the area or multiple refrigerant types, infra red technology, which is very specific to the particular refrigerant being used, is a more suitable choice.

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10. Ammonia monitoring
Ammonia is used as a refrigerant primarily in application requiring very low temperatures such as food processing or ice arenas. Solid-state sensors are useful for leak detection, but if TLV detection is required, electrochemical technology is much more effective.

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11. Mining and mineral processing
Mining and mineral processing pose several requirements for gas detection, from methane pockets within coal beds, to products of combustion from both vehicle operation and blasting byproducts, to hydrogen cyanide in gold processing.

Methane
Methane is formed by the decomposition of organic matter.  It is the most common hazardous gas in the mines, contributing to more than 10,000 miner deaths during the past 60 years, predominantly in coal mines, where large pockets may be present. Methane is found in most underground mines.  Since it is lighter than air, methane tends to rise to the roof of a mine or tunnel.

Methane injures and kills in two different ways:

• It asphyxiates (suffocates) you when there is too much of it in the air (by crowding out the oxygen you need to breathe).
 
• It explodes when ignited by a flame or even a spark.

Carbon Monoxide
CO should be tested every day in underground mines: Absence of smoke does not mean CO isn’t present.  A smol­dering fire may kill before it ever breaks out into flames, as it did in the Sunshine Mine disaster, taking 91 lives. CO is a byproduct of vehicle exhaust and can result from blasts Symptoms of CO poisoning are headache, dizziness, and lack of coordination and judgment.  CO poisoning makes strong, healthy people weak and unable to help others.  Carbon monoxide is also present in smelting and blast furnace applications.

Hydrogen Sulfide
Hydrogen sulfide, or stink-damp (H₂S), is a highly poisonous gas common in both coal and metal/nonmetal mines.  Harmful quantities are often found in gypsum mines, tunnel digging, caissons, and it may be mixed with natural gas.  Hydrogen sulfide is easily absorbed by water, and then released when the water is disturbed.  When H₂S is known to exist in a mine, be careful when removing floodwater, and don’t allow water in drainage ditches to move very far. When you first smell hydrogen sulfide, it stinks like rotten eggs—but the gas also diminishes your sense of smell.

Hydrogen Cyanide
Gold typically occurs at very low concentrations in ores - less than 10 g/t or 0.001%. At these concentrations the use of aqueous chemical extraction processes is the only economically viable method of extracting the gold from the ore. Gold is one of the noble metals and as such it is not soluble in water. A complexant, such as cyanide, which stabilizes the gold species in solution, and an oxidant such as oxygen are required to dissolve gold. Fumes of hydrogen cyanide may come from this process, resulting in unsafe levels in the workplace.

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