THE DAMAGE DONE BY NOISE

Dominion, Volume 34, Issue 80, 28 December 1940, Page 2

THE DAMAGE DONE BY NOISE

Psychological Effects COUNTERING SERIOUS SIDE OI- AIR ATTACK The unprecedented noise of modern warfare was one of the factors which contributed to demoralization iu Flanders and the North of France. Many persons who had never heard such noise before and were unprotected against it were terrified or numbed, writes the science correspondent of the “Manchester Guardian.” An understanding of the degree and nature of danger from noise and of methods of protection against it has become an important part of preparation for withstanding attack. Dr. T. S. Littler, of Manchester University, has given an interesting review of the problem in “Nature,” and it has been subject of research specially by students of the effects of noise on pilots. The effects of noise may be classified as psychological and physical. The whistles sometimes attached to bombs produce noises which do no damage to the ear but are intended to frighten. The psychological effect is enhanced by surprise, so such whistling bombs will not be used regularly but after intervals in which their use has been temporarily forgotten. If the noises are sufficiently intense they may do physical damage to the ear. Sound travels by a wave of compression through the air, and it is heard through the alternations of the pressure of the air on the eardrum. The more intense the sound the higher the pressure with which the waves of air beat upon the eardrum. IVhen this pressure rises above a certain limit, which is related to the frequency of the incoming wave, the sensation of sound is accompanied by a feeling of pain. The pressure at which high notes produce discomfort is much lower than that at which low notes produce discomfort. In fact, the ear will tolerate a booming note of frequency 30 to 100 a second five times as loud as a shriller note of frequency 200 to 7000 a second. Air Pilots and Noise. Aviators in modern aircraft are exposed for long periods to noises that may be sufficiently intense to produce pain. It has been found that if pilots fly for an hour or more in a modern machine without any protection for the ears thev become severely deafened to higher notes with a frequency above 2000 a second. Normal hearing for the higher notes returns after rest, though the habit of flying without ear protection makes the partial deafness permanent. The victim may be unaware of his condition, as it is manifested by a decrease in the clarity rather than the loudness of sounds. If the pilot wears a satisfactory helmet or ear plug, he does not suffer from temporary deafness, and even several thousand hours of flying do not impair his hearing. The ear protectors cut oft very efficiently the high notes that produce the most painful effects, though thev are largely transparent to the less disagreeable low notes. They do not appreciably reduce the ultimate pressure on the eardrum, but they reduce the rate of rise of the pressure, so that the ear receives a less damaging, though scarcely less loud, sound. Sustained loud noises, specially or an irregular type, have a definite fatiguing effect. They reduce the efficiency of workers from 1 to 20 per cent. They inhibit the normal contractions of the intestine and stomach and reduce the flow of saliva and gastric juice, fl’liis is one of the causes of the frequency of gastric illnesses in pilots and others subject to loud noises. Protection of the ears against the sustained irregular noises of the present onU" aircraft barrages is important for the prevention of indigestion and stomacfi trouble. , . . Aviation engineers have given increasing attention to the protection or pilots and passengers against noise, and the trend of their developments is in the direction of soundproof cabins and away from ear plugs. This suggests that the best protection against bomb and gun noises is the deep, soundproof shelter. . , The deafening caused by bomb explosions is of the same nature as aviators’ deafness. It is caused chiefly by the high notes in the noise, and appears to be associated with the same physical damage to the s J ru^ tul TJ’J the inner ear. It seems that actual rupture of the tympanic membrane by a very big noise or blast is less serious than‘might be imagined, as the membrane usually heals rather rapidly. The Best Ear Plug. Dr. Littler quotes some figures of experimental tests on tbe efficiency o seven tvpes of ear protection. These consisted of flying helmets ear defenders made of hard materials, fingeitips held in the ears, cotton wool saturated with vaseline, liquid parafli ami cotton wool saturated with vaseline, liquid paraflin and cotton gauze saturated with vaseline, and the packing of the ears with a plastic clay. The best results in tiiese experiments were given by the liquid paraffin and cotton gauze saturated. with vaseline. Cotton wool soaked in vaseline is useful, but ear plugs made of hard material are not advisable, as they are liable to produce irriIn addition to plugging the e.tis it is advisable to bile a piece of rubber or resilient material. This prevents the full shock of the explosion being transmitted to the inner ear through the bones of the skull The eftects of blast are also mitigated by relaxing the muscles of the face, which reduces the rigidity of any exposed part, and hence the ease with which the blow may be conveyed to sensitive organs such as the inner ear. Experiments with animals seem to qhow that more damage is done to the ears by vibrations transmitted through the bony framework of the body than bv I he sound waves that enter the external ear. Popofl! placed a cage of mice on the floor of a factory where steel bars were hammered into scythes anil- suspended a second cage of mice bv a spring from the ceiling. When the ears of the two groups of mice wore examined eight months later it was found that those of the mice in the cage on the floor were seriously damaged, while those in tire springsuspended cage were still normal, ihis showed that the loud noises coining through Ihe air had done no barm, while the vibrations transmitted through the materials of the floor ami the bones of the mice in contact with it had been destructive. These results, and others of the same kiud, suggest that during air raids it is wise to protect oneself against vibration and concussion. One should not sit on a bare stone floor or lean against a brick wall, but. if possible, sit on cushions mid place them between the back and the wall. Holding pillows over the chest and face at the moment of approaching explosion may also help