" With very basic and readily available technology, dust levels in A/C plants can be kept well within the internationally established guidelines."

A/C pipe is manufactured by the Hatchek/ Mazza process from an intimately mixed aqueous slurry of portland cement (80-85%) and a mixture of relatively long and medium grade chrysotile asbestos fibres (15-20%). The slurry is dewatered by a machine using a rotary sieve cylinder and a continuous felt to produce a very thin layer of asbestos cement which is wrapped around a mandrel under pressure until a pipe with the desired wall thickness is produced. The mandrel is then extracted and the pipe is cured by passing through a tunnel-like low temperature oven followed by immersion in or spraying with water, or by autoclaving. After curing, the ends of the pipe lengths are cut and finished to receive couplings that are produced by cutting larger diameter pipe into sections.

A/C pipe is manufactured under carefully controlled conditions in order to achieve a smooth internal finish. The incapsulated asbestos fibres act as a reinforcing material to form an intrinsic part of the cement matrix.

PROVIDING A SAFE WORKING ENVIRONMENT

The effective control of chrysotile asbestos dust in the work place can eliminate health risks to workers. In the manufacture of asbestos cement products most of the processes are "bound-in" or wet. When the asbestos is present in a slurry (a wet mixture) there is no possibility of dust emission. Such processes require only relatively simple safe work practices often referred to as "housekeeping". These include: wetting of the process where applicable; immediate and proper clean-up of waste generated by the process; vacuuming or wet removal of all dust particles generated; and avoiding practices such as dry sweeping which generate dust. These dust control techniques are well-known, easily available and require relatively inexpensive and unsophisticated equipment. The capital and operating costs of these methods consist of only a small fraction of the total costs of the plant. (21)

Dust emissions from other components of the manufacturing process can also be easily controlled. The use of enclosed debagging stations as asbestos is introduced into the process and suction hoods during the cutting and finishing of A/C pipe ensure that airborne particles are captured and contained. Much of the waste collected during the production or housekeeping process can then be reintroduced into the system, thus avoiding environmental pollution and saving on raw material costs. (22)

Frequent monitoring of the work place environment and periodical medical assessments of the workers will verify that the techniques in place are effective. The implementation of a dust control program can produce highly effective results using only the most basic of techniques. Processing such as wetting and vacuuming can dramatically decrease dust levels in plants which may previously have had ineffective or minimal controls. The implementation of local exhaust ventilation and filtration systems will further lower dust levels.

Source: A/C Pipe Producers Association - Article

References:
(21) Bragg, G.M., Dust Control Engineering in the Workplace, Paper presented at the International Conference on Asbestos Products, Kuala Lumpur, Malaysia, 1991.

(22) Pattabhi, V., Low-Cost Dust Control Techniques in Asbestos Cement Industry, Paper presented at the International Conference on Asbestos Products, Kuala Lumpur, Malaysia, 1991.