American Laboratory | Year: 2015
The National Fire Protection Association's Compressed Gases and Cryogenic Fluids Code (NFPA 55), International Fire Code (IFC) and International Building Code (IBC) maximum allowable quantities (MAQs) for hydrogen are discussed. NFPA 55: Compressed Gases and Cryogenic Fluids Code MAQs offers two variations based on whether or not the building has sprinklers and whether or not all hydrogen cylinders are stored in gas cabinets. The specified volumes are expressed as standard cubic feet (ft3) of hydrogen at 1 atmosphere of pressure; for buildings without sprinklers, the MAQs are limited to 1000 ft3 where not all cylinders are housed in gas cabinets. NFPA 55, IBC and IFC requirements permit a greater volume inside a building, as long as significant upgrades are made to the building's structure, fire rating, limitations on occupancy, transport, fire detection and allowable number of stories. NFPA 55 mandates that fire-resistance rating, ventilation, separation and controls are below the MAQ for hydrogen installations. Piping, tubing, valves, fittings and related components are to be designed and fabricated from materials that are compatible with the material to be contained and are to be of adequate strength and durability to withstand the pressure, structural and seismic stress and exposure to which they are subject.
Pollution Engineering | Year: 2014
Experts discuss the details of the process and physical property differences of common stainless steel surface treatments and the impact on gas chromatography performance. They state that Tunable Diode Laser Absorption Spectroscopy can detect HF down to 0.2 parts per million meters (ppmm) and HCl to 0.15 ppmm. This chromatograph technique operates on the principle that gas molecules absorb energy at specific wavelengths. Stability of the calibration standards at these low levels is impacted by the regulator and the tube's material, metallographic composition, and surface finish. Other processes such as electrochemical polishing will remove the unwanted surface iron oxides and will cause surface peaks to yield an extremely smooth, microscopically featureless surface.
Pollution Engineering | Year: 2010
Vacuum control is vital for the detection of impurities such as moisture, oxygen, hydrocarbons or other constituents, and to ensure product quality and workplace safety. The necessary components of the sampling system include span and zero gas standards to provide an NIST-traceable reference for calibrating the detector. The first stage receives cylinder inlet pressure and delivers the gas to the second stage at a preset value that is typically between 225 and 400 psig. As the inlet pressure decays, the output of the first stage increases because of less closing force acting upon the seat. This enables the system's vacuum pump to create a negative pressure on the regulator's outlet cavity. The system also has a non-compensated variable-area flowmeter designed to deliver a constant amount of calibration or sample gas to the detector. Finally, it may be necessary to include a sub-atmospheric backpressure regulator between the detector and vacuum pump that limits the amount of vacuum applied to the entire sampling system.
American Laboratory | Year: 2011
MFM200 thermal mass flowmeters and MFC202 thermal mass flow controllers offer higher accuracy and direct traceability of flow measurement or control that is not hampered and is minimally impacted by changes in pressure or temperature. The thermal mass flow devices use the heat transferred by a moving gas to determine the flow of that gas. As the gas flows, it causes the temperature of the downstream sensor to increase. The flow is measured by comparing the difference in the temperature sensors. The thermal mass flow technique renders a measurement that is essentially unaffected by the gas pressure or temperature. The readings are directly proportional to the 0-5 V return signal in the case of the mass flowmeter units, and the flow is controlled with the same input signal of 0-5 V against the full scale of the mass flow control units. The thermal mass flow is the technology that gives the highest precision with directly traceable results to a known and recordable standard.
American Laboratory | Year: 2013
The first step in any properly sized laboratory or facility's gas requirement is to determine the daily demand for that gas. It would begin by totaling the amount of gas containers onsite and considering how many are delivered each week or month. For new operations, each use location should also be evaluated to determine the total expected daily requirement for CO 2. The key to comparing the flow of 6 lpm of gaseous CO2 per incubator must be weighed against the duty cycle of how often the door is opened in an hour of daily use compared to how often the door remains closed over that 24 -hr period. For bioreactors, the demand, though required to be uninterrupted during operation of the reactor's batch or cycle, is not required to be available 24/7 , but rather only during duration of use. As with any bulk or sizable liquid cylinder installation, area oxygen deficiency monitors should be installed in storage or use areas, and any pipeline-relief valves should be piped to an appropriate exterior vent line as per NFPA 50 and building safety code requirements.
American Laboratory | Year: 2012
Selecting gas delivery systems for safety, performance and cost efficiency in the laboratory is a challenging task. There are a number of codes and standards that apply to the storage, use, and installation of gases and their delivery systems, and they should be kept in mind. As a minimum, gas cylinders should be stored and secured in an upright position using brackets, chains, or straps in a well-lit and ventilated area away from combustible materials and sources of heat or ignition. When determining what size pipe or tubing to use for a specific application, the main consideration is to determine what the maximum required flow for that specific gas would be if all application or use points were flowing to their maximum at the same time. For almost all laboratory gases, maintaining gas purity is a critical requirement. To that end, the choice of materials of construction and their compatibility with that specific gas and its purity level must be considered.
American Laboratory | Year: 2014
The origins of specific areas that pose challenges and the type of gas systems and equipment that need to be employed to ensure a safe atmosphere for the staff and the work environment are discussed. During transfer operations, the rate of liquid nitrogen is dependent on how insulated and how well the supply side of the operation delivers the liquid in a stable state, as well as how and where the liquid that vaporizes during the transfer is vented. If we consider that each liquid cylinder of 230-L volume contains 5000+ cubic feet of gas at standard temperature and pressure and a typical cryogenic freezer may contain an additional 3000-5000 cubic feet of gas, it is imperative for any area to have an effective oxygen-deficiency monitoring system. The other hazard that should be addressed is the use and storage areas for flammable gases like hydrogen, as well as potentially toxic gases like hydrogen sulfide or carbon monoxide. There are four main areas required by NFPA 55 for these types of installations, such as fire-resistance rating, ventilation, separation, and controls.