Page 3 - Combined_8_OCR

Tolylene Diisocyanate Manufacturing Chemists’ Association, Inc. Manual
Sheet
SD-73

are exposed to the atmosphere. The volume of air 4.4 AIR ANALYSIS
mechanically exhausted must be such that the hood
face velocities are within acceptable limits (100 ft. 4.4.1 A threshold limit for tolylene diisocyanate
per minute per square foot of hood opening or more). vapor has not yet been fully determined, but pre­
The type of hood to be used will depend upon the liminary animal tests indicate 0.1 ppm. is safe. A
particular application, and the ventilation system concentration which can be smelled (approximately
should be designed by experienced engineers. The 0.1-1.0 ppm., varying with the individual) is too high
following design principles should be adhered to: for continuous exposure.
(a) The exhaust hood should be located as 4.4.2 A calibrated indicator for the detection of
close as possible to the source of the escaping vapor. tolylene diisocyanate vapor is commercially avail­
able. This unit is portable and can be used to make
(b) The process should be enclosed as much spot checks • around tolylene diisocyanate handling
as possible.
equipment.
(c) Baffles and side shields should be used to
the fullest. A colorimetric method is also available in which
a known volume of test air is pumped through an
(d) The velocity of air at the point of vapor absorber solution. The intensity of coloration of
dispersal should be sufficiently high to capture the the solution is a quantitative measure of the presence
vapor particles. This is an especially important con­ of tolylene diisocyanate vapors.
sideration in the case of tolylene diisocyanate vapors,
which are six times as heavy as air and tend to flow 4.5 ELECTRICAL EQUIPMENT
downward.
All electrical equipment and wiring should be in
(e) Advantage should be taken of air move­ compliance with the National Electrical Code. Wir­
ment due to thermal currents. ing for ordinary locations is suitable.
(f) Vapors should not be drawn past the oper­
ator’s face. 4.6 ADDITIONAL PRECAUTIONS
Care should be taken to prevent tolylene diisocya­
(g) The hood should be positioned so that it
does not interfere with the operator’s work. nate from coming into contact with basic compounds
such as caustic soda, tertiary amines, or other similar
materials. This might cause uncontrollable poly­
4.3.3 Pouring from Containers
merization of the isocyanate. The heat given off
When it is necessary to pour tolylene diisocya­ in such a reaction could result in rapid vaporization
nate from a can or drum, a temporary lid fitted with of any low boiling solvent that might be present.
a flexible hose leading to the exhaust system should A build-up of pressure and even rupture of the con­
be placed on the container. taining vessel may follow. If a strong base and water
are present, carbon dioxide will be liberated, again
resulting in a pressure build-up.
4.3.4 Area Ventilation
The introduction of an acidic compound such as
In some cases, the process equipment in which benzoyl chloride or acetyl chloride will control poly­
tolylene diisocyanate leaks might possibly occur is too merization. However, only minor amounts of acidic
extensive to be enclosed by an exhaust hood. Thus materials should be added, perhaps, 0.01-0.02 per
mechanical ventilation of the entire room may be cent chlorine. In some cases large amounts may
necessary. A down-draft type of ventilation is most cause more rapid polymerization. The best measure
desirable, since tolylene diisocyanate is six times as is to take the necessary precautions to prevent poly­
heavy as air. merization from occurring.

5. EMPLOYEE SAFETY

5.1 EMPLOYEE EDUCATION AND TRAIN­ can create an undue hazard. An effective employee
ING education should include the following items:
5.1.1 Employee training is probably the most (a) The operator should be thoroughly familiar
important safety measure a company can take. Al­ with the process with which he is concerned, as well
though the company may provide the best in the as the hazards that exist.
way of protective equipment and expend great effort
to be sure that each process or operation is designed (b) He should be instructed in proper handling
with safety in mind, an improperly trained worker procedures for the chemicals involved.