SynopsisThe influence of molecular weight and temperature on the tensile drawing behavior of polypropylene has been studied, with particular reference to the production of ultra-high-modulus oriented materials. It has been shown that the optimum draw temperature is molecular weight independent to a good approximation, and that high-modulus products can be obtained for mw in the range 180,000-400,000, the highest modulus being achieved for polymer with Bw = 181,000. As in the case of linear polyethylene, under optimum drawing conditions the Young's modulus relates only to the draw ratio. Low-temperature moduli as high as 25-27 GPa were recorded, which compare favorably with a previously reported value of 42 GPa for the crystal-lattice modulus. Although the drawing behavior of the samples studied appeared comparatively insensitive to molecular weight, some of the properties of the draw materials, notably melting point and shrinkage at high temperature, showed a wide range of behavior. on-Thames, United Kingdom.

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R . W. SARSBY M r D. Foster, West Yorkshire Metropolitan County CouncilSince January 1976, when Part 111 of the Control of Pollution Act came into force, the West Yorkshire Metropolitan County Council has undertaken some 65 contracts on civil engineering and building works, in which clauses based on BS 5228 have been included. Ih' each case the anticipated noise levels from construction operations were predicted using the methods outlined in BS 5228, and subsequently a CEL 162 noise analyser and a B&K 4426 noise level analyser were used to measure both period and cumulative L., values. Our results have confirmed Mr Sarsby's conclusion that there is good correlation between predicted and recorded values and that in general the prediction method is likely to give levels slightly in excess of those measured. I would support the approach taken by Mr Sarsby in calculating noise levels at the initial stages by the block method as being the most practical method; it is the method we have used, and our analysis has shown that that approach gives a reasonably good indication of possible future problems.49. The Control of Pollution Act is not primarily concerned with noise levels but with disturbance which may result from these levels. The findings of Mr Sarsby's study therefore should be used to predict construction noise levels with confidence and then to assess the results in terms of disturbance.50. Mr Sarsby comments that at properties adjacent to a motorway construction site the L., levels were below 75 dB(A) and were therefore generally not excessive. While it may be true that noise levels up to 75 dB(A) in a particular situation may be acceptable, they cannot be taken as being acceptable in the general situation.51. Disturbance by construction noise cannot be determined solely by the particular noise level, but must also be related to the ambient level of the area. In considering industrial noise, BS 4142 states that complaints may be expected if industrial noise exceeds background noise by 10 dB(A) or more. In a rural situation background levels may well be below 50 dB(A) and thus a 12 h L., of 75 dB(A) would represent an extremely severe increase in noise.Conversely, where other noise sources exist (e.g., by roads), the ambient level may already be fairly high and thus an L., level of 75 dB(A) may not be excessive. It should also be noted that in the urban and semi-urban situation, construction works are often close to properties and L,, levels in excess of 75 dB(A) are experienced at property facades. It is in these situations where the more serious construction noise problems usually occur.52. In order to overcome disturbance, the approach that has been operated for the past three years by the West Yorkshire County Council is that the limiting levels are agreed for each contract by the county council in conjunction with the environmental health officers of the district councils. These control levels are related to the facade

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