The risks of damages and diseases for the human organism in the textile industry can have following causes:
1) unhealthy microclimate: this is the case in particularly of the dye-houses, the environment of which is characterized by a high humidity level and by the presence of more or less harmful or irritant fumes, which are often associated with high temperatures and with an insufficient change of air. Also in certain spinning departments the necessary humidity rate, often combined with a certain presence of dust in the air, can result in breathing problems. The fibre dust which is emitted mostly when processing vegetal fibres can cause, in the more sensible subjects, an irritation of the bronchus, associated with a continuous production of mucus, and originate with the time chronic diseases as pharyngitis, tracheitis and bronchitis;
2) noise: noise represents in various departments and above all in weaving mills a problem of primary importance, especially if there is not enough room available and no dequate
soundproofing intervention on the machine and on the rooms have been carried out. In such cases the alternative is the use of individual safety devices. A high noise level can entail a reduction in the functions and other secondary collateral effects;
3) illumination, working position, precision, rhythm, repetitiveness, turnover system: various tasks require a considerable stress on the sight, or need body postures which have to be maintained long time, or require much attention, rapidity of execution, repetitiveness at very short intervals, temporary adaptations which can be the source of various pathologies both at physical and at psychical level.
Noise in the weaving rooms
In the textile industry, the noise problem in the various working departments is a cause of serious concern. The highest noise levels are to be found in the weaving rooms, where the operators are exposed to levels of 94 to 100 dBa. The needs of having the possibility to control fabric quality prevent any casing or partial shielding of the weaving machines, it is however possibile to correct the acoustics of the working room. The mostly used materials are:
1. glass wool baffles put in a glass fabric envelope and hang up on the ceiling;
2. glass fibre panels with an interspace between panel and adjoining wall;
These measures, unfortunately, are not very effective, so that the personnel is anyway compelled to use the devices for individual protection. In fact these measures reduce the noise level only by 1 to 1,5 dBa between the weaving machines and by 2 to 3 dBa between the beams and in the department passageways. The above mentioned modest results, typical of the weaving rooms, are due to the preponderance of the direct waves (coming from the noise sources) over the waves which are reflected by other bodies and to the distance of the sound absorbent material from the noise sources. The devices for individual protection which the workers have to use against noise are of various types and give different results with the variation of the frequency. There are devices which protect better at high frequency values (1000-8000 Hz) and others which are more efficient at low to medium frequency 125-1000 Hz).
Noise origin and problems in weaving machines
Noise is caused by the vibration of the mechanical parts of the machine. These parts can be either in motion (various kinematic motions) or standing (structural parts, boxes, casings). The moving parts are the main origin of vibrations, which are then transmitted to the other parts of the machine. The vibrations are the higher, the more intense are the load variations to which the moving elements are submitted: sley, heald frames, weft inserting elements.
These movements are alternative motions and have rather high operation frequency levels; as such motions generate the maximum load variation values on the involved mechanical elements, it is easily understandable that the resulting vibrations and the pertaining noise, can attain very high values.The noise of a machine depends therefore to a very large extent on the operating speed but also on the machine equipment viz. on its composition, as this entails a different quantity and typology of the mechanical units, each with different vibration mode. For this reason the weaving machine manufacturers are following two well known basic lines in their production:
1. noise reduction already at the designing stage;
2. reduction of the noise reaching the operator by means of physical barriers between the noise sources and the subject (casings).
A further possibility could be, as previously indicated, the modification of the mill acoustics. In fact, although a great deal of progress has been accomplished to reduce noise in the weaving rooms, there is still a long way to go.
We need only to consider that the noise emitted by a modern rapier machine is about 90 dBa (maximum level of acoustic pressure in 8 hours per day for a single person at 1 meter distance from the machine surface) when the machine turns at 500 strokes per minute without screenings, viz. the same noise level emitted by an old shuttle loom running at 180-200 strokes/minute. Thanks to the technological development, the weaving speed in the last 20 years has more than doubled, however without increasing the level of acoustic pressure. The attention which most of the industrial countries give today to the issue of environment pollution is more than justified. The noise is not only annoying, but can be harmful to health and at the end increase the social costs.
The EEC guideline Machines 89/392 draws the attention to this problem and invites the manufacturers to design machines in such a way, that the risks due to noise emission are reduced to a minimum, in consideration of the technical progress and of the technical means available to reduce the emissions at their source. This guideline obliges the manufacturers to declare the noise levels emitted by their machines. The noise evaluation of a single weaving machine is anyway not sufficient; in the textile mills dozens, not to say hundreds, work simultaneously in one and the same weaving room and the sound level increases in proportion to the number of looms, even exceeding the threshold of 90 dBa indicated by the present Italian legislation.
The graphics here below show the noise increase in relation to the variation in the intensity of the sound produced by a certain number of sources positioned side by side. You can note that, with 8 noise sources at 89 dBa, the noise level on a central measurement point is equal to 89 dBa; in the case for instance of two noise sources, by increasing the noise level of each source by 5 dBa, we get a variation in the central point of 2 dBa.In the third graphic, if we bring the same noise sources to 90 dBa, we get a central point at a level of 94 dBa. This variation in the value of the central detection point in relation to the change of the sound level of the two noise sources follows a logarithmic trend.