The dust hazard in air-pressure abrasive blasting (sandblasting)

Summary of Conclusions

• 1. When air-pressure abrasive blasting is conducted in enclosed devices (barrels, tables, cabinets and automatic rooms) employing sand as the abrasive the air of the workroom generally contains a highly hazardous dust concentration. The dust itself contains an average of over 90 per cent of quartz and the average dust count of the room atmosphere averages over 20 million particles per cubic foot. Such an atmosphere cannot fail to predispose in a high degree to silicosis.

• 2. When steel instead of sand is used in such devices as the abrasive material, the dust counts average from 8 to 15 million particles and the quartz content falls to 3 per cent. Such conditions as this should not cause silicosis with any reasonable period of exposure.

• 3. Even with the use of sand abrasive, our studies show that all the four types of equipment studies can be made safe by proper construction and maintenance. We were able to observe the operation of barrels, tables and cabinets which the designers had previously indicated as of ideal modern design. In all cases the dust content of the air in the neighborhood of these devices averaged less than 2 million particles.

• 4. In rooms, where the worker must operate in the actual midst of the sand blast, the dust content is, of course, enormous, varying from 48.8 million with steel abrasive, to 327.2 million particles per cubic foot (average 155.0 million); and, with sand abrasive, from 232.0 million to 3,104.0 million particles per cubic foot (average 969.0 million).

• 5. Helmets depending on filtration are quite inadequate to protect the worker against such dust concentrations; and positive air-pressure helmets with wire mesh eye-screens are irregular and unreliable in their effect.

• 6. On the other hand, positive air-pressure helmets with glass eye-shields and an air supply of6 cubic feet per minute furnish complete protection to the worker under the worst conditions found in actual operation, yielding a dust content of less than 1 million particles per cubic foot within the helmet, with 1,000.0 million or more particles per cubic foot in the outside air and rising only to 3 million particles per cubic foot within the helmet even when the outside air contains 4,000.0 million particles.