4220 Flow Meter
Appendix D General Safety Procedures

D-6

number of harmful vapors. They, too, are sensed by smell and

explosimeter tests if they get into the public sewer. Such occur-

rences are rare.

“The attempt to instill a sense of urgency about real hazards is

diluted if a man is told to give attention to a long list of things

that in fact are irrelevant.

“Be very careful to avoid high H2S concentrations, flammable

atmospheres, and hazards of physical injuries. Remember that

much H2S may be released by the stirring up of sludge in the

bottom of a structure. Obey your senses in respect to irritating

gases, such as chlorine (unconsciousness comes suddenly from

breathing too much). Be cautious about strange odors. Do not

determine percent oxygen in the air. There is a danger that the

result will influence a man's thinking about the seriousness of

the real hazards. Most important, use ample ventilation, and do

not enter a potentially hazardous structure except in a good

safety harness with two men at the top who can lift you out.”

D.3 Hazardous Gases The following table contains information on the properties of

hazardous gases.

Table D-1 Hazardous Gases
Gas Chemical
Formula
Common
Properties
Specific
Gravity
or Vapor
Density
Air =1
Physiological
Effect
Max
Safe 60
Min. Exposure
ppm
Max. Safe
8 Hour
Exposure
ppm
Explosive
Range (% by
vol. in air)
Limits
lower/upper
Likely
Location
of
Highest
Concentration
Most
Common
Sources
Simplest and
Cheapest
Safe Method
of Testing
Ammonia NH3Irritant and
poisonous. Col-
orless
with characteris-
tic
odor.
0.60 Causes throat
and
eye irritation at
0.05%, cough-
ing
at 0.17%. Short
exposure at
0.5%
to 1% fatal.
300
to
500
85 16 25 Near top.
Concentrates
in closed up-
per spaces
Sewers,
chemical
feed
rooms.
Detectable
odor at low
concentrations
Benzene C6H6Irritant, colorless
anesthetic
2.77 Slight symp-
toms
after several
hours
exposure at
0.16% to 0.32%.
2% rapidly
fatal.
3,000
to
5,000
25 1.3 7.1 At bottom. Industrial
wastes,
varnish,
solvents.
Combustible
gas indicator
Carbon
Bisulfide
CS2Nearly odorless
when pure, color-
less, anesthetic.
Poisonous.
2.64 Very poison-
ous,
irritating, vom-
iting,
convulsions,
psychic distur-
bance.
— 15 1.3 44.0 At bottom An insecti-
cide
Combustible
gas indicator