Lower explosive limits

Odor Characteristic Characteristic Characteristic and detectable at cone. > 20% lower explosive limit (NF EN 589, Appendix A)... 

The explosive limits of hydrazine in air are 4.7—100 vol %, the upper limit (100 vol %) indicating that hydrazine vapor is self-explosive. Decomposition can be touched off by catalytic surfaces. The presence of inert gases significantly raises the lower explosive limit (10) (Table 2). 

Table 2. Lower Explosive Limits of Hydrazine in Other Gases...

Undesirable combustible gases and vapors can be destroyed by heating to the autoignition temperature in the presence of sufficient oxygen to ensure complete oxidation to CO2 and H2O. Gas incinerators are appHed to streams that are high energy, eg, pentane, or are too dilute to support combustion by themselves. The gas composition is limited typicaUy to 25% or less of the lower explosive limit. Gases that are sufficiendy concentrated to support... 

Isoprene is classified by the ICC as a flammable Hquid requiring a red label (124). Its flash point is —54°C with a lower explosive limit (LEL) of 1.5%... 

Cross-country gas pipelines generally must odorize the normally odorless, colorless, and tasteless gas ia urban and suburban areas, as is required of gas distribution companies. Organosulfur compounds, such as mercaptans, are usually used for this purpose, and code requires that the odor must be strong enough for someone with a normal sense of smell to detect a gas leak iato air at one-fifth the lower explosive limit of gas—air mixtures. The latter is about 5%, so the odorant concentration should be about 1%, but most companies odorize more heavily than this as a safety precaution. 

The lower flammable limit (LEL) or lower explosive limit (LEL) is the minimum concentration of vapor in air below which a flame is not propagated when an ignition source is present (61—64). Below this concentration, the mixture is considered too lean to bum. The lower flammable limit and the flash point of a flammable Hquid are closely related by the Hquid s vapor pressure characteristics. 

OSHA and ACGIH have not estabhshed specific airborne exposure limits for PVB and PVF resias however, some products may contain sufficient fines to be considered nuisance dust and present dust explosion potential if sufficient quantities are dispersed ia air. Unformulated PVB and PVF resias have flash poiats above 370°C. The lower explosive limit (lei) for PVB dust ia air is about 20 g/m. ... 

Table 7. Lower Explosive Limits Range for Coating Powders...

There are situations where thermal oxidation may be preferred over catalytic oxidation for exhaust streams that contain significant amounts of catalyst poisons and/or fouling agents, thermal oxidation may be the only technically feasible control where extremely high VOC destmction efficiencies of difficult to control VOC species are required, thermal oxidation may attain higher performance and for relatively rich VOC waste gas streams, ie, having >20 25% lower explosive limit (LEL), the gas stream s explosive properties and the potential for catalyst overheating may require the addition of dilution air to the waste gas stream (12). 

Some vent streams, such as light hydrocarbons, can be discharged directly to the atmosphere even though they are flammable and explosive. This can be done because the high-velocity discharge entrains sufficient air to lower the hydrocarbon concentration below the lower explosive limit (API RP 521, 1997). Toxic vapors must be sent to a flare or scrubber to render them harmless. Multiphase streams, such as those discharged as a result of a runaway reaction, for example, must first be routed to separation or containment equipment before final discharge to a flare or scrubber. 

For combustible dusts, the explosibility limits do not have the same meaning as with flammable gases and flammable vapors, owing to the interaction between dust layers and suspended dust. This protective measure can, for example, be used when dust deposits are avoided in operating areas or in the air stream of clean air lines after filter installations WTiere in normal operation the lower explosibility limit is not reached. However, dust deposits must be anticipated with time. When these dust deposits are whirled up in the air, an explosion hazard can arise. Such a hazard can be avoided by regular cleaning. The dust can be extracted directly at its point of origin by suitable ventilation measures. 

The lower explosive limit (LEL) is the minimum concentration of a vapor in air that will support a flame when ignited. The flash point is the lowest temperature of a liquid that produces sufficient vapor for an open flame to ignite in air. 

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). 

Flammable or Explosive Limits — the upper and lower vapor eoneentrations at whieh a mixture will bum or explode. The lower explosive limit of p-xylene is 1.1 pereent by volume in air, whereas the upper explosive limit is 7.0 percent in air. A mixture of p-xylene vapor and air having a coneentration of <1.1 pereent in air is too lean in p-xylene vapor to bum. Conversely, a mixture containing more than 7.0 percent is too rieh in p-xylene to bum. By subtraetion (7.0 - 1.1), p-.xylene is said to have a flammable range of 5.9. Materials having low explosive limits and wide flammable ranges are extremely dangerous. 

Oxygen, the second requirement for combustion, is generally not limiting. Oxygen in the air is sufficient to support combustion of most materials within certain limits. These limitations are compound specific and are called the explosive limits in air. The upper and lower explosive limits (UEL and LEL) of several common materials... 

Low flow, low concentration streams are best handled by a catalytic recuperative oxidizer. When the concentration of the stream is between 15% to 20% LEL (Lower Explosion Limit) then both a catalytic recuperative or thermal recuperative is the best technologies. For process streams between 20% to 25% LEL then thermal recuperative is the preferred solution. 

The volatile solvents recoverable by the activated carbon system or any other system are nearly all organic, and many of them form flammable or explosive mixtures with air. Such mixtures may lie between upper and lower explosive limits. The activated carbon system can avoid the explosive range by staying well below the lowest percentage of vapor which is still explosive it functions well at very low concentrations. The system also recovers solvents efficiently even in the presence of water the recovery efficiency is high (98 percent and 99 percent are not unusual) it may be fully automatic. The annual maintenance charge rarely exceeds 5 percent of the cost of equipment. The recovery expense may be as low as 0.2 cent per pound in some installations it rarely exceeds 1 cent per pound. 

Flammable Limits in Air - This is a concentration expressed as percent by volume of the chemical in air, whereby spontaneous combustion will be supported. The lowest concentration where combustion will be supported is known as the lower flammability limit (LFL) or lower explosion limit (LEL). LEL and LFL are considered interchangeable. The upper concentration limit is the UFL (Upper Flammability Limit) or UEL (Upper Explosion Limit). 

Flare Gas - Molecular weight, lower explosive limit, density at flare tip, fraction F of heat release radiated by the flame. 

Cl = Lower explosive limit concentration of flare gas in air, volume fractions... 

Let s now mm attention back to the flammability limit itself. When small increments of a combustible gas are successively mixed with air, a concentration is finally attained in which a flame will propagate if a source of ignition is present. This is referred to as the Lower Flammable Limit (LFL or lower explosion limit) of the gas in air. As further increments of the gas are added, a higher concentration of flammable gas in air will finally be attained in which... 

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