When performed carefully with the use of proper equipment, there should be no dust problem during the transport of asbestos-cement sheet or pipe from the plant or warehouse to the construction or installation site. Nevertheless, normal precautions must be taken to prevent the creation of dust. For example, scraping (e.g. by hoist chains) and other abrasion must be avoided. Also, any accidental breakage must be removed immediately to avoid the creation of dust by vehicles driving over the broken material.
Special precautions must be taken when installing asbestos-cement sheet and pipe in the field, i.e when using sheet in construction and when laying pipe into the ground. This is necessary because both sheet and pipe are often cut, sawed, drilled or bored during the installation process. All these actions produce a considerable amount of dust if proper tools are not used.
Cutting asbestos-cement products is a particular problem because it is usually performed at the construction or installation sites by untrained workers who are not sufficiently aware of the potential hazard associated with the use of asbestos. Also, if precautions are not taken, other workers at the construction site will be unnecessarily exposed to asbestos dust.
A specific problem exists with respect to the installation of asbestos sheet. This problem is caused by a process called mitring, i.e. cutting a mitre at one corner or the top and bottom corners on opposite sides. This is done to avoid an overlap of four corners and the possibility of rain penetration at this point.
In some cases, mitring is done at the asbestos-cement sheet plant. Three types of sheets must be produced to allow proper installation, i.e. sheets with one corner mitred, sheets with two corners mitred (top and bottom on opposite sides), as well as sheets without mitred corners. This is necessary to cover the ends as well as the edges of the walls and the roof of a building.
Since this requires considerable planning during manufacturing, warehousing and installation, etc., and because different mitre angles may be required, mitring is often done at the construction site. Unfortunately, a great deal of dust is generated by this process because of the tools used for this purpose. For example, the tool primarily used for mitring is the disc grinder which removes the corners of the asbestos-cement sheets, by grinding the corners down to the required line. Therefore, the corners are not cut off but instead are pulverized by grinding. Needless to say, a great deal of dust is created in the process. This obviously exposes the worker performing the task to considerable risk. In addition, the dust accumulates on the floor and is distributed throughout the construction site affecting other workers.
Because of the potential hazards involved, manufacturers recommend that high-speed tools never be used when cutting or drilling A/C products. Indeed, in order to avoid cutting at construction sites, most manufacturers are pre-cutting or pre-drilling products prior to their leaving the factory.
Where cutting must be carried out at the construction site, hand tools should be used as much as possible. For example, mitring can be done by using shears that break the asbestos-cement into chips. Alternatively, simple hand saws with large teeth that produce a very coarse dust can be used. Also, the drilling of holes (when punching is not possible) can be performed by hand drill that produce coarse shavings because of the low speed. These materials can be cleaned-up by wet sweeping and require no special precautions.
If disc grinders, hand-held power saws, etc. are used in the field, a centrally located, separate building should be provided. Each piece of equipment should be fitted with a properly designed hood that is connected to an HEPA vacuum system. Clean-up of the interior of the building can be accomplished by using the HEPA vacuum system. In general, abrasive or masonry disc grinders should never be used, unless equipped with a HEPA vacuum system. If so equipped, there is no need for workers to wear HEPA respirators. However, such equipment should be provided to workers upon request.
If a vacuum system is not available, water should be used for dust suppression. When using this approach, the asbestos-cement sheets should be wetted and water should be sprayed onto the saw blade. The blade should run at the lowest speed possible and a blade with large teeth should be chosen. This produces large cuttings rather than fine dust. Again, chips and shavings can be cleaned-up by wet sweeping.
The hand-held, rotating band saw, developed by the Neuss Institute in Germany, may be used for wet cutting because it operates at a low speed and the saw teeth are large.
Saws with vacuum attachments should be used in a separate building.
Finally, the sheets must be fitted with holes to accommodate the required bolts or nails that secure the sheets to beams and joists. If drilling is used, the drill must have a vacuum attachment to collect dust, and the drill should run at low speed. Another method is to puncture holes with a sharply pointed hammer, such as the so-called roofers hammer.
A better procedure for installing asbestos-cement sheet is the offsetting system. This means that the adjacent sheets in the first course (layer of asbestos-cement sheet) of a wall or roof are overlapped as usual, but the next course is offset, one corrugation to the left or right. The third course is offset two corrugations, etc.
For this method, one or two corrugations must be trimmed from the front sheets of the second or third course. This should be done by scoring and breaking of the sheet instead of sawing. The break produced is not as smooth as a saw cut, but this is a small price to pay for avoiding a dust problem.
In regard to this approach, it is possible to punch a hole by using the bolt intended for securing the sheet. The holes produced in this manner are not as even and uniform as drilled holes, but there seems to be no problem in terms of appearance or safety.
During the installation of asbestos-cement pipe, it is frequently necessary to shorten the length of pipes or remove broken pipe ends. This is done by hand tools that either crack or cut the pipes. There is minimal dust generated when pipes are cracked as cutting produces relatively large chips because of the low speed at which the cutting tool operates. As a further precaution, the pipes may be wetted. Obviously, all asbestos-cement debris must be collected and properly disposed of. The use of high speed abrasive disc saws for cutting pipe in the field is not recommended, regardless of whether new installations or repairs are involved.
The ends of the pipes that are cut are usually reduced in diameter using a manual lathe. Where this is not required, the edges of the pipe may be bevelled manually using a rasp. In both cases, relatively large chips of asbestos-cement are created.
Manual lathes can also be used to cut grooves into couplings. This is usually done for repair jobs rather than new installations. In this connection, removal of couplings from old pipes should be done by chiseling to avoid creating dust.
If holes must be cut into pipes to install connections, this may be done manually using simple tools. There are also manually and power operated machines for the boring of pipes that carry water under pressure. It is not expected that dust problems arise during these operations as long as normal precautions are taken, including appropriate clean-up.
Cleaning up
At the end of the work, the work area should be cleaned of any asbestos-cement dust or debris. In particular:
a) Waste and debris must be cleaned-up and disposed of as soon as possible. Fine debris, dust waste or waste which is liable to generate dust should be placed in suitable closed containers which prevent the escape of asbestos dust, e.g. heavy duty polyethylene bags. When the container is full it should be effectively sealed, the outside cleaned and placed in a separate storage area for disposal. Containers should be labelled to show that asbestos is present. Larger pieces of asbestos-cement, including whole sheets should not be broken or cut for disposal in plastic sacks. These materials should be carefully transferred to covered lorries or skips, if they are dusty or crumbly, they should be wrapped;
b) External surfaces of waste containers must be cleaned before removal from the work area;
c) All surfaces in the work area must be cleaned by a suitable dustless method. Where practicable, use a vacuum cleaner fitted with a high efficiently filter to collect dust. Where this is not appropriate, wet dust and debris thoroughly (i.e. not merely sprinkled with water) before brushing or shoveling up into strong plastic bags. Provided appropriate work practices are followed, it is not necessary to provide workers HEPA respirators, although such should be made available upon request.
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