General Equipment EP8HL, Руководство оператора

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Definition of Flammable (Explosive) Limits
Flammable limit, like flash point, is an important index
of the relative hazards of the various gases and
vapors.
There are minimum and maximum concentrations of
flammable gases or vapors above and below which the
mixture will not burn or explode. The Lower Limit is
where the substance is too "lean" to burn or explode
and the Upper Limit is where it is too "rich" to burn or
explode. For example, hydrogen is too lean to ignite
below a 4.0 percent concentration and too rich to ignite
above a 75 percent concentration. However, the Upper
Limit should not be taken as a measure of safety,
because as gases or vapors are released, they reach
concentration levels within the explosive range before
they reach the Upper Limit. Explosions of a flammable
vapor-air mixture near the Upper Limit or Lower Limit
are less intense than those occurring in the
intermediate concentrations of the mixture.
The flammable limits shown in the following tables are
based on normal atmospheric temperatures and
pressures, unless otherwise indicated. At higher
temperatures, the Lower Limit would be lower and the
Upper Limit higher; that is, the explosive range would
be wider.
Definition of Vapor Density
This is the weight of a volume of a vapor or gas with no
air present compared to the weight of an equal volume
of dry air at the same normal atmospheric temperature
and pressure. Vapor densities are ordinarily used only
to determine the settling or rising tendency of a
mixture. A figure of less than 1.0 in the following tables
indicates that the vapor is lighter than air and will tend
to rise. A figure greater than 1.0 indicates the reverse.
Examples of lighter than air gases are methane natural
gas and hydrogen gas, which the tables show to have
respective densities of 0.6 and 0.1. These gases in
indoor locations tend to concentrate near the ceiling
where lighting fixtures, for example, are customarily
mounted. At the other extreme are heavier than air
mixtures, like ethyl ether vapors, that may travel at low
levels for a considerable distance to sources of
ignition. CAUTION: certain substances, while perhaps
not extremely hazardous in pure states, react violently
with other materials. For data on such substance, see
NFPA Manual of Chemical Reactions, 491M-1991.
EXPLANATIONS OF THE FOLLOWING CLASS I
GAS AND VAPOR TABLES.
Data on Class I gases and vapors presented in the
following tables contains the latest information
available from NFPA at the publication date of this
manual. The data is based primarily on NFPA 497M-
1991, Manual for Classification of Gases, Vapors and
Dusts for Electrical Equipment in Hazardous
(Classified) Locations with additional data secured
from NFPA 325M-1991, Fire Hazardous Properties of
Flammable Liquids, Gases and Volatile Solids. These
publications are the latest available on these subject
areas from NFPA at the publication date of this manual.
The data on explosive properties of Class I gases and
vapors is as follows:
TABLES I and II. These are flammable chemicals with
flash points below 100˙F and are therefore the most
hazardous. Normally, special electrical equipment is
required where these flammable chemicals are
present, as these substances form ignitible or
explosive mixtures with air at ambient temperatures.
TABLES III and IV. These are combustible vapors with
higher flash points than the flammable gases and
vapors listed in Tables I and II. The flash points of
vapors in Table III range from 100˙F and flash points of
vapors in Table IV range from 140˙F or more, but less
than 200˙F.
EXPLOSIVE PROPERTIES OF CLASS II
COMBUSTIBLE DUSTS.
The following tables depict ignition temperatures of
classified combustible dusts. Ignition temperatures are
shown because they are the criteria used by NEC®
and UL® for classifying heat producing equipment,
such as lighting fixtures.
Ignition Temperature Definition
Ignition temperature is defined as the minimum
temperature required, at normal atmospheric
temperatures in the absence of spark or flame, to ignite
a dust layer or dust cloud.
Ignition temperature is tested in two ways:
a) Layer Ignition Temperature
b) Dust Cloud Ignition Temperature.
EP8HL HAZARDOUS BLOWER
FORM GOM7069501, VERSION 1.2
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