Page 36 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

A Gases and Vapors
Gases: Normally formless fluid which occupy the space of enclosure and which can be changed to the liquid or
solid state only by the combined effect of increased pressure and temperature gases diffuse. The particle size
varies from 0.0005 to 0.01 micron.
Example are chlorine, ammonia, sulfur dioxide, Hydrogen sulfide (H2s), Hydrogen cyanide, carbon monoxide,
etc. Main pollution are oxides of carbon, sulfur and nitrogen.
Vapors: The gaseous form of substance which are normally in the solid or liquid state and which can be changed
to these states by either increasing the pressure or decreasing the temperature alone. Vapors diffuse. The particle
size varies from 0.005 to 0.01 micron.
Examples are vapours of lead oxide, benzene, xylene, trichloroethylene, and other solvents.
Gases and vapors are also classified as under
• Organic solvent vapors e.g. alcohol acetone, CS2, CCI4, benzene, xylene.

• Pulmonary irritant gases e.g. CL2, NO2 and phosgene.
• Upper respiratory irritant gases NH3, SO2, formaldehyde, acetic acid.
• Chemical asphyxiant gases CO, CHN.
• Simple asphyxiant gases H2. CO2, methane, its homologues and acetylene.

• Other inorganic and organic gases H2S, arsine and pesticides vapors.
B Particulate Matters:
These are solid tiny particles produced by blasting, crushing, drilling, grinding, mixing etc. and suspended in air.
Examples are as under:
a Dust: Solid particles generated by handling, crushing, grinding, rapid impact, detonation and decrepitating
of organic or inorganic materials such as rocks, metal, coal, wood, grain etc. Dusts do not tend to flocculate
except under electrostatic forces. They do not diffuse in air but settle under the influence of gravity. The particle
size varies from 0.1 to 1000 microns. Fly ash from chimneys varies from 3 to 80 microns.
b Fumes: Solid particles generated by condensation from the gaseous state, generally after volatilization from
molten metals etc. and often accompanied by a chemical reaction such as oxidation. Fumes flocculate and
sometimes coalesce. The particle size varies from 0.001 to 100 microns. Examples: lead, zinc. or nitrous
fumes.
c Mists: Suspended liquid droplets generated by condensation from the gaseous to the liquid state, such as by
splashing, foaming and atomizing. The particle size varies from 50 to 100 microns. Example: sulphuric acid
mist.
d Smokes: Small gas-borne particles resulting from incomplete combustion and consisting predominantly of
carbon gaseous material are grouped in this category. The particle size varies from 0.1 to 1 micron.
e Smog and Fog: The air contaminants may be present in the forms of smog and fog which are not usually
encountered in an industrial environment. The particle size varies from 1 to 50 micron.
f Aerosols: It is a colloidal system in which the dispersion medium is a gas and the dispersed phase is solid
or liquid. The term aerosol is applicable till the solids or liquids remain suspended in the gaseous media.
The particle size varies from 0.01 to 100 micron. Dust, smoke or mist are examples. Aerosols affect weather,
damage materials and impair health. Atmospheric aerosol like hydrocarbons, lead, arsenic, sulfuric acid etc.
may injury human health because of their toxic nature.
• Permissible exposure Limit:
• Set by OSHA, 29 CFR, 1910.1000, and 1910.1001 through 1910.1450.
• Specify the maximum amount of concentration of a chemical to which a worker may lie exposed.
• Generally, define in three different ways (Salary limit, Short term expose limit & time weighted average).

• Concepts of Threshold Limit Values (TLVs):
• Prepared by ACGIH volunteer scientists.

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CITS : Automotive - Mechanic Diesel - Lesson 01 - 04