Toxic gas detection

Brandon RW. 1983. The use of chemically impregnated paper tapes for toxic gas detection and monitoring. Anal Chem Symp Ser 17 726-731. 

Another type of monitor is a field mounted hazardous or toxic gas detection device. Such permanent gas detection systems (see Figure 11-7) protects personnel and equipment finm virtually any toxic or combustible gases through audible and visual alarms in the field and/ or on a control board. Permanent gas detection systems consist of a combination of transmitters, intelligent sensors, controllers, and accessories. These types of monitors are used to ... 

Instrument Society of American (ISA).ANSI/ISA-92.00.02, Installation, operation, and maintenance of toxic gas-detection instruments. ISA 2013. 

Toxic gas detection should be installed if the potential exists for toxic gas accumulation in a tank area, or else entry into a bermed area must be treated as a confined space entry. 

Where air-conditioning equipment is used for buildings within 150 meters of hydrocarbon processing plants, features such as flammable or toxic gas detection and heating, ventilation, and air-conditioning (HVAC) shutdown, in addition to the location of the air intake, should be considered in order to protect personnel and equipment in the building from toxic or flammable vapors. 

Toxic gas detection should be provided in the HVAC inlet of any occupied building where release scenarios and dispersion modehng indicate potential gas concentration above the short-term exposure limit (STEL). 

Detailed information to do with toxic gas terminology and the effects of these gases on the human body are provided in Process Risk and Reliability Management Much of the guidance to do with flammable detectors can be applied to toxic gas detection also. However, the following additional issues should be considered ... 

Nickel Carbonyl The extremely toxic gas nickel carbonyl can be detected at 0.01 ppb by measuring its chemiluminescent reaction with ozone in the presence of carbon monoxide. The reaction produces excited nickel(II) oxide by a chain process which generates many photons from each pollutant molecule to permit high sensitivity (315). 

Safety and security Temperature Toxic gases like CO, CO2, exhaust gases, smoke,. .. Combustible gases like CH4, C2H6 (gas detection via flame detection (Europe), fire detectors, caravans with gas detectors) UV sensors Radon sensing... 

Air intakes to heating and ventilation systems, air compressors for process, instrument and breathing air, and to prime movers for gas compressors, power generation and pumps should be located as far as practical from contamination by dust, toxic and flammable materials release sources. They should not be located in electrically classified areas. If close to possible vapor releases (as confirmed by dispersion analyses( they should be fitted with toxic or combustible gas detection devices to warn of possible air intakes hazards and snutdown and isolate the incoming air ductwork and fans. 

Alarms should be initialed by the local or main control facility for the location. Manual activation means should be provided for all emergency, fire, and toxic vapor alarm signals. Activation of fire suppression systems by automatic means should also indicate a facility alarm. Most fire and gas detection systems are also set to automatically activate alarms after confirmation and set points have been reached. Manual activation of field or plant alarm stations should activate the process or facility alarms. 

So, what is so unusual in this pale yellow highly toxic gas that condenses to a pale greenish-yellow liquid at -188°C, solidifies to a yellow solid at -220°C, has a strong ozone-like odor, and is easily detectable at concentrations about 0.1-0.2 ppm(= ml/m3).5... 

Once it is determined that flammable gas detection is needed for a processing area, an evaluation of the gas/liquid composition of each credible release can be done. The formation and behavior of gas clouds is primarily governed by whether the material is released as a gas or as a liquid. In order to properly locate detectors, the expected behavior of a gas cloud must be understood. Similar considerations apply to the release of toxic materials and the appropriate location of detectors for these materials. 

Where it is possible for flammable or toxic gas or vapor released within a hazardous area to migrate to the inlets for HVAC systems serving nonhazardous enclosed areas such as control rooms, detection systems should be installed in those HVAC inlets or connecting ductwork. Detection should be provided in HVAC system intakes if the building, room, or enclosure served is not electrically classified and a flammable (or toxic) gas or vapor could feasibly be drawn into the area, either by mechanical ventilation systems or by differential pressures. The detection system should alarm and automatically shutdown the HVAC to prevent gas or vapor concentration in the protected space from reaching the flammable or toxic range. 

Sensor—Field measurement system (instrumentation) capable of detecting the condition of a process (for example, pressure transmitters level transmitters, and toxic gas detectors). 

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