Explosive Limits Monitoring

The need to remove all flammable material from the area should be considered. Where this is impractical, checks on its containment and inerting are necessary, together with environmental monitoring to ensure that atmospheric levels are well below the lower explosive limit (Figure 13.3). 

Natural gas detectors should reliably detect the presence of gas concentrations far below the lower explosion limit of about 5% vol. In Germany many different cheap gas alarm systems can be purchased in DIY-market, but most of these devices are not based on any quality standard. Although high priced alarm and monitoring systems are available there is a lack of low cost reliable gas alarm systems for use in households which are based on appropriate standards. 

Improvement Item LEL (lower explosive limit) and standard 02 levels monitored by ACHMT, indicating crash scene impact only. Chlorine could have been indicated with proper monitoring equipment. ACHMT was not effectively integrated into Haz-Mat operations. Decontamination areas were not monitored due to lack of Haz-Mat support at decontamination locations. 

VOC concentration monitors which control air flow to each dryer stage to maintain the dryers at 25-40% of the LEL (lower explosive limit)... 

The plant is controlled by a process computer (ABB-Hartmann and Braun) and equipped with numerous data-collecting instruments. Surveillance is carried out by continuous analysis of the room air as well as by explosion-limit controls. The pyrolysis gas is analyzed automatically by a gas chromatograph. All data obtained are registered to enable calculation of energy and mass balances. Some basic components are continuously monitored by infrared spectroscopy, i.e. ethylene in the pyrolysis gas, sulphur dioxide and oxygen in the exhaust gas. 

The flash photolysis of PH3-O2 mixtures was studied by Norrish and Older-shaw bothabovethe upper and below the lower explosion limits. They monitored PH2, PH, OH, and PO by absorption spectroscopy. The only intense spectra were from PH2 and PH at short delays. The only other spectra were from PO and OH and they were always weak. The mechanism proposed by them was... 

Safety caution the production of hydroperoxides should always be performed with caution. In our case with 100% molecular oxygen, we worked above the explosion limit, and monitored the oxygen uptake by a burette, making sure that the conversion stayed below 40%. Laboratory glassware was used behind safety screens, and the scale was limited to 10 ml solutions. Hydroperoxides were stored at 4°C as dilute solutions, with the corresponding alkylbenzenes as solvent. 

An instrument designed to detect the presence or concentration of combustible gases or vapors in the atmosphere. It is usually calibrated to indicate the concentration of a gas as a percentage of its Lower Explosive Limit (LEL) so that a reading of 100 percent indicates that the LEL limit has been reached. They use either a solid-state circuit, infrared (IR) beam electrochemical or duel catalytic bead for the detection of gas in an area. Portable monitors are used for personnel protection, and fixed installations are provided for property protection. The Instrument Society of America (ISA) has provided a guideline for combustible gas detector utilization, ISA TR 12.13.03, Guide for Combustible Gas Detection as a Method of Protection. 

Explosive gases should be monitored for concentrations above the lower explosive limit. 

Monitoring should be conducted to determine if there is a possibility of a "gassy" situation below, that could cause an explosion. If the person who monitored for gassy situations determines that a hazardous situation exists, the employer is responsible for taking the proper action. If an individual determines that 20 percent of the lower explosive limit for a gas has been detected, then all personnel should be removed from the area except those necessary to resolve the problem. 

Declassification to potentially gassy operations. Underground construction gassy operations may be declassified to Potentially Gassy when air monitoring results remain under 10 percent of the lower explosive limit for methane or other flammable gases for three consecutive days. 

Concentrations of solvent vapor, which is heavier than air, adjacent to the vapor degreaser and in the work area should be continuously monitored using an explosimeter (Figure 3.22). The standard is that these volumetric concentrations are to be no more than 25% of the posted lower explosive limit (LEL). 

An alarm system is in place to alert the operators to the presence of hydrogen in the containment and the consequential need to activate the hydrogen igniters. The hydrogen sensors is able to monitor the range of hydrogen concentration from well below the flammability limit up to and beyond the explosive limit. 

The systems typically monitor for methane (concentration range of 0-100% lower explosive limit (LEL)) and carbon dioxide (concentration range of 0-5% by volume in air) but this will always be site specific and should take accoxmt of the specific gases present in the groxmd below a site. 

The vapor-laden air feed to the system is usually filtered at the inlet of the recovery plant to prevent dust or other particulate matter from entering the activated carbon bed. The concentration of solvent vapors in the air entering most solvent recovery units ranges from about / to 2 Ib/cu ft. With flammable solvents, fire-hazard considerations limit the maximum allowable solvent concentration. This should be less than 50% of the lower explosive limit (LED when continuous monitoring is used, and less than 25% of the LEL when intermittent monitoring is employed (Parsons, 1988). Data on LEL for organic compounds are available from the Underwriters Laboratories, Inc. Values for common solvents in air are given in Chapter 13 (Table 13-4). 

Determine if dilution air is required to assure that the concentration of combustibles in the feed gas to the incinerator system is less than 2S% of the Lower Explosive Limit (LEL), or less than S0% if continuous monitoring is employed. LEL and heat of combustion data for a number of compounds are given in Table 13-4. If dilution air is required, calculate the amount and the total quantity of feed. 

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