Introduction

The best source for current health and safety information is the pigment manufacturer. Consult the current safety data sheet. Pigments serve many beneficial functions in modern society and technology. Irrespective of their end use, they are not considered consumer chemicals, but are primarily directed to a variety of industries. They are processed into products such as paints, printing inks decorative cosmetics, pharmaceuticals, food and plastics, which are then directed to other indus-tries and then on to their respective consumer markets. Industry has the responsibility to be informed of the potential hazards associated with its raw materials so that suitable measures may be taken to insure the safety of employees, customers, the public, and the environment. This section of the Handbook summarizes the available safety and health information for pigments. The section features eight tables of data derived from documented case histories and toxicological testing of specific pigments. The key to the tables is given in the Regulatory data section of the individual Data Sheet for the appropriate pigments.

Although the tables are restricted to documented studies of specific pigments, the discussion covers the risk potential of pigments in general or of their constituents. For the benefit of the interested reader, an extensive bibliography is provided which contains references of general interest in addition to those cited in the tables or the text.

The number of references for a given pigment is not to be construed as an indication of hazard potential. The survey of health-oriented literature uncovered relatively few articles for organic pigments. Most organic pigments have a comparatively short history of commercial usage and thus it is not surprising that there is more accumulated literature on inorganic pigments. In the discussion, it is presumed that the pigment is a dry powder without surface treatment. No attention was paid to the risk potential of vehicles, solvents, and other materials used in the preparation of various pigment grades. In either case, with appropriate handling procedures, engineering controls and personal hygienic practices, no pigment of any grade should pose a health risk to the industrial worker.

Safety Considerations

Under normal circumstances, pigment dry colors are nonflammable and unreactive chemicals. It is important, however, to appreciate that there are certain abnormal circumstances associated with the storage and/or use of pigment products, under which hazardous situations may occur. This section covers three such circumstances: excessive heat, dust explosion, and chemical reactivity.

Excessive heat

Most pigment dry colors in the Handbook are classed as nonflammable by definitions given in OSHA and DOT regulations and do not require a shipping label. Some dry colors, however, are currently classed by DOT as self-heating substances defined by a proscribed test procedure and must be labeled accordingly. Some of the pigments are so heat-stable that, given other essential features, they qualify as fire extinguishers of the dry chemical type. Talc (P. White 26) and barytes (P. White 22) have both been mentioned in this respect. Although pigments are not readily ignitable in bulk, Material Safety Data Sheets issued by producers indicate that the majority will burn support combustion or decompose with the emission of dense smoke if involved in a fire from other sources or if heated to sufficiently high temperatures for sufficiently long periods of time.

If the oxidation process is exothermic, the resulting fire may be very difficult to extinguish. A classical case is ferrous oxide, a constituent of black iron oxides. Also listed in Table B1 is Dinitraniline Orange, which smoldered and burned as a result of overheating during processing, apparently above its decomposition point of 310°C. (Reports of fires involving two other organic pigments were received; they are not listed because they were resinated products.) In lieu of autoignition temperatures, clues to ease of combustion (or of decomposition) may be provided by composition, melting point, and baking stability. Transition metals, such as iron, lead, manganese and cobalt, are known to catalyze oxidation, therefore, pigments based on these metals should be expected to support combustion. Among organic types, some azo pigments melt (or sublime) at temperatures as low as 250°C, but the process of decomposition starts at much lower temperatures, as evidenced by color degradation in baking stability tests conducted at 150°C. Some non-azo salts are also in this category. The fighting of fires involving pigments must always be carried out with due regard for the possibility of toxic smoke emissions. By definition, all organic pigments contain carbon, the oxidation products of which include carbon dioxide and the highly toxic carbon monoxide. Among the special concerns recognized by producers on their MSDS are the burning of calcium pigments which, at 890 °C, produces calcium oxide (quicklime), and the thermal decomposition of organic pigments containing amino, bromo, chloro, iodo, nitro and sulfo groups. It must also be pointed out that, because of their smaller particles sizes, fumes are more respirable than dusts. According to Sax (11), any chemical containing a nitro group constitutes a moderate explosion hazard if heated under confinement. A precautionary statement to this effect appears on the MSDS of a few nitro containing pigments, but no case history information has been uncovered.

Because of the hazard potential in case of fire, it is recommended that pigments be stored in moderately cool, dry, well-ventilated areas, away from flammable materials. Firefighters should be instructed to wear selfcontained breathing devices and to employ extinguishing techniques that do not create dusts or are otherwise appropriate to the fire conditions. Advance discussion with the local fire department is a recommended practice.

Dust Explosion

A dust explosion is essentially a very rapid combustion of charged suspended particles during which heat is generated at a much higher rate than it is dissipated to the surroundings. Finer airborne particles increase the risk of explosion because they remain suspended longer and their greater surface area permits more rapid oxidation and static charging. Metallic dusts are reported to be more susceptible because they may react not only with oxygen but also with nitrogen in the air to form nitrides. Of the three metallic pigments in the Handbook, explosion related data were found only for aluminum and zinc. Aluminum dusts are rated as high for explosion potential, the lower explosive limit (LEL) being 35 mg/m3. The LEL is over 400 mg/m3 for zinc dust, which is rated as a moderate explosion hazard. The presumably low rating for the third pigment, copper dust (P. Metal 2), is attributed to its high conductivity and its corresponding ability to dissipate static charges and heat.

It is important to recognize that any operation generating excess dust may be subject to dust explosion. In addition to metallic pigments, both organic and inorganic pigments may also present a risk of dust explosion. Precautionary statements to this effect are given on many of the MSDS for pigments.

Excellent checklists of specific measures to prevent dust explosions are provided by the Aluminum Association Bulletin and other information sources cited in Table B1. One measure is to keep airborne dust below the LEL; note that conforming to the OSHA standard (15 mg/m3 for nuisance dust) may well serve both purposes. Secondly, since combustion is an inherent part of explosion, it is essential to eliminate sparks and any other source of ignition, both usual and unusual. Because of the possibility of static buildup, special care should be taken when handling pigment powders in flammable solvent atmospheres or in close proximity to flammable materials.

Data not compiled

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