The best industrial ventilation system or any other type of well engineered system designed to improve the working environment and reduce the amount of dust generated can be easily defeated by bad work practices of the operators or employees. Each person is different by nature, experience, intelligence, attitude, etc. The result of personal dust samples carried out on two employees working side-by-side, handling the same product on the same type of machine can be extremely different because of the way they work. It is very important when a dust control program is initiated in a factory that, at the same time, work practices of each employee be analyzed. There is no easy method by which the work habits of all employees can be quickly changed. Each one has to be dealt with so that within a reasonable time he begins to show improvement. The key to making employees "dust conscious" is information and training. This is discussed in another chapter of this manual.
The work practices necessary in all parts of the plant are straightforward. These work practices include wetting where such a process is applicable, clean-up of any waste generated during manufacturing, vacuuming or wet removal of all chips and small pieces throughout the plant and enforcement of straightforward regulations such as forbidding dry sweeping and the use of compressed air for cleaning purposes. Needless to say, good work practices are as important as all other efforts made in order to provide a dust-free working environment.
Housekeeping is unquestionably the most important of all dust control methods. Simply cleaning-up all possible emission sources as quickly as possible is the most effective dust suppression technique. Such practices as vacuuming and wet floor cleaning not only prevent high dust levels, they also improve already clean, efficiently controlled asbestos-using environments. By introducing these simple housekeeping techniques, a factory can reduce dust levels by half or even three-quarters. Good housekeeping and work practices require workers' time. Because they are labour intensive rather than capital intensive, they can be used in plants working at any level of technology.
As in all other issues of health and safety at work, good housekeeping will only be achieved if both management and workers are committed to it. It is important that workers' representatives be involved in the discussions about housekeeping problems and possible solutions.
Storage, Transportation, Handling of Bags
Asbestos is usually delivered in 50-kilogram, or less, pressure-packed plastic or paper bags, which are combined into 1-tonne lots of 20 bags and placed on wooden pallets. The bags are covered by shrink or stretch-wrapped plastic for extra protection during shipping and warehousing. Pallets are shipped to the asbestos-using plants in containers, by truck, rail or ship. They are then unloaded (and removed from the containers) by forklift truck, hoist, crane, hand, etc., and stored in a warehouse which is either part of the plant or located immediately adjacent to it.
Problems with respect to dust control arise immediately upon arrival of the asbestos fibre shipment because there are bags that may be damaged in some way. This results in fibre being spilled on the floor of the truck, railroad car, vessel or inside the container. The spill should be removed by vacuuming using a HEPA vacuum cleaner. After taping the broken or cut bags, the pallets can be unloaded and transported to the warehouse.
It should be kept in mind that the outside of unbroken bags in the vicinity of the spill are often contaminated with fibres that must also be removed by vacuuming before the pallets are moved to the warehouse. This is most conveniently done by moving the contaminated bags to a special clean-up building adjacent to the unloading site. If contaminated bags are moved into the main storage building or into the plant, contamination is usually the result.
If the spill is a major one, the unloading crew must wear protective clothing as well as respiratory protection. Special HEPA vacuum equipment may be needed if the normal vacuum system associated with the plant cannot be used. The purpose of the special equipment is to transfer the spilled fibre into bags to be properly disposed of. In case of any spill, the truck, container, etc., used to ship the asbestos, should be cleaned prior to leaving the plant site.
If bags are damaged while stored in the warehouse, severe contamination will occur. Corrective measures are difficult because many areas in the warehouse cannot be reached. Even under the best circumstances, a well managed warehouse should be cleaned regularly using appropriate HEPA vacuum equipment.
Prevention of Spillage/Spread of Contamination
Too often housekeeping problems are tackled from the wrong end. The response to a process which causes asbestos to spread over the floor, workbench, etc., is normally to simply introduce regular cleaning to remove the spillage. Although this is necessary, the real effort should be put into finding and resolving the cause of the problem. Additional protection for the worker may be necessary during this period.
Think about the process. It may be possible to prevent the spillage by a change in work method, a redesign of the plant or even a change of process. It will be difficult to change long established work practices. Involvement and cooperation of the workforce is essential and retraining of operators will be needed. This provides a strategy for tackling housekeeping problems. When spillage or spread of asbestos is found, act along the following lines:
Investigate
Examine the process in detail to find the cause of the spillage/spread. Remember that the problem may be at an earlier operation. The operator should be involved as he or she may be aware of the cause. Additional cleaning should be introduced to cope with the problem in the meantime.
Eliminate or Reduce Spillage
Once the cause or causes are known every effort should be made to eliminate, or if this is not possible, reduce the spillage. This can be done by:
(a) changing the process;
(b) changing the working method; or
(c) providing improved containment around the process. If possible the waste collected should be automatically removed.
Make Cleaning Easier
If it is not possible to prevent spillage, steps should be taken to make cleaning easier. This could range from providing trays or bins to collect the spillage to making the floor below the process smooth and eliminating ledges, etc.
Successful prevention usually needs a combination of both improved plant design and working method. However, designers should make plant suit the way people work and move rather than expect them to adapt their working methods to cope with a poorly designed machine. Even when a process is partly automated, careless or unsatisfactory work practices will often result in spillage or spread of contamination. It will help employees and supervisors if correct methods of working are laid down in written job procedures or systems of work.
Cleaning Techniques and Procedures
There are two vital points if cleaning is to be done well and as safely as possible. They are:
(a)the cleaning method should be dustless (in other words no asbestos dust should escape into the air either from the cleaning action or from the cleaning equipment); and,
(b) the cleaning should be done often enough and at the appropriate time.
In order to achieve this, a combination of suitable and sufficient equipment, good procedure, adequate supervision and monitoring is needed.
The traditional method of cleaning was with a brush or broom. But this creates a dust cloud even if the brush is damp, or oiled, or water is sprinkled on the material to be swept up. This happens because dust rapidly builds up on the brush and it becomes effectively dry again. Brushing or sweeping is NOT a dustless cleaning method and should not be used.
Equipment and Techniques
There are different types of equipment which can achieve dustless cleaning if they are used correctly and properly maintained. They are listed below in order of preference, with an indication of the advantages and disadvantages of each one.
€ Fixed Vacuum Installations:
Such an installation consists of a central source of suction and dust collection connected to a network of fixed pipes which have connection points for cleaning hoses and attachments in all parts of the building served. Proper design and installation is essential and should only be tackled by qualified contractors.
As with all other cleaning systems, it is important that it is readily available for use in every area which it serves. At the time of planning a system, it is necessary to balance the convenience of having numerous connection points against the additional cost of each extra point. However, the problems which will arise from an under-designed system suggest that it is better to have too many connection points rather than too few.
Cleaning should be organized to prevent too many points being used at the same time. If too many are used together they will not work effectively because the suction will be too low.
The advantages and disadvantages of fixed vacuum cleaning installations can be summarized as follows:
Advantages
- relatively little maintenance
- centralized collection of waste
- reasonable running costs
- easy operation
Disadvantages
- high initial costs
- failure can cause relatively serious problems (all connections out of action)
- still need back-up by portable systems
€ Portable Vacuum Cleaning Equipment
This type of equipment is self-contained having its own suction fan, filter unit and dust collection bag. There must be enough of them so that they are readily available in all.areas that require service. They also need to be sufficiently portable to allow cleaning of difficult and restricted spaces. The number will depend to some extent on the way cleaning is organized.
Advantages
- lower capital cost
- more versatile and flexible
Disadvantages
- continual maintenance
- potential hygiene problems during dust bag changing
- traling electric cables
- trailing electric cables
€ Mobile Floor Cleaners
This type of equipment usually includes a powerful suction and filtration unit connected to a floor cleaning attachment. Some types also have a rotary brush. Not all types of floor cleaners will be capable of dustless cleaning or will have an adequate standard of filtration. Therefore careful assessment is needed when selecting such equipment for use in asbestos contaminated areas.
Despite these reservations, such equipment may be the only practical way of cleaning large floor areas and gangways in a reasonable time. They should NOT, however, be used as an alternative to portable vacuum cleaners, for other types of cleaning.
Advantages
- clean large areas quickly
Disadvantages
- some types may not be dustless
- doubtful filtration standard
- emptying waste collection bins/trays is dusty and will require the use of protective equipment
€ Other Techniques
Wet cleaning techniques can be dustless, providing that they are genuinely "wet" and not just "damp". The waste to be cleaned up must be thoroughly wetted and kept wet until it is in a sealed container. The wet waste should be scraped into a collection tray or bin. Alternatively, wet waste can be washed or sucked into a collection sump and disposed of as liquid waste by a specialist contractor.
Asbestos Waste
Waste collected during cleaning should be put into a suitable container such as a heavy duty plastic sack. The container should be closed and sealed and should be labelled "Asbestos waste". The label should also indicate the type of asbestos. The local waste disposal authority should be consulted for advice on correct methods of disposal.
Procedure
Having ensured that the right equipment and techniques are available for dustless cleaning, it is essential that they are properly used and maintained. For this to happen employees must know what they have to do and how to do it. Supervisors/managers must monitor how well it is done. It will usually help if the procedures are laid down as a written system of work. This should deal with responsibilities for cleaning, maintenance of equipment and monitoring in general terms. The detail of how and when to clean particular areas can be given in separate cleaning schedules.
Responsibility for Cleaning
The responsibility can be placed on individual employees, a specialist employee (or team) or a combination of these. One system cannot be said to be better than the others ‹ rather the allocation of employees to cleaning duties needs to be matched to the equipment and techniques provided. The most important point is that the responsibility should be clearly laid down in written procedures and schedules.
Cleaning Schedules
Cleaning schedules should be prepared for all areas, machines, etc. Therefore, every effort should be made when planning cleaning procedures to stagger the cleaning times throughout the premises. There are advantages for both cleaners and supervisors if cleaning schedules are displayed at the machine, in the area to which they relate.
FIGURE 9 shows the historical behaviour of two work stations at a single asbestos-cement pipe plant. These data show that dust control is an evolving process. Alterations, improvements, and reconsideration of the methodology of control are always necessary. As can be seen by following each operation from year 0 to year 14, changes and improvements were achieved. As the figure indicated, in later years the control was sufficiently effective that the dust levels were at or below the level detectable by the optical microscope method (about 0.2 f/cc).
4.5 - PERSONAL PROTECTIVE DEVICES
In many situations, particularly those dealing with maintenance, repair and equipment failures, it is not possible to ensure low dust levels at all times in the plant environment. As a result, respirators and special clothing may occasionally be required. Use of respirators should be regarded as a temporary or emergency measure only and not as an alternative to other control procedures. The more common types of respirators can be uncomfortable for extended periods. In fact, workers frequently refuse to wear them except for short periods.
For emissions which are above the recommended permissible exposure limit value, appropriate respirators fitted with replaceable filters are necessary. Workers should be informed of when and why a respirator must be used, and the importance of using it continuously and properly. The correct procedures for the use and verification of protective equipment should be demonstrated. The subject of "Personal Protective Equipment" is thoroughly covered in a further section of this manual.
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