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SALBU FARM Private Bag X2352, Wingate Park, 0153, R.S.A.

Date : Friday, October 17, 1997
To Fax No. : 011-800-3089 011-629-5644
Company : ESKOM
Attention : Mr A J Morgan Phone 011-800-5510 - cc Mr AC Britten Phone 011-629-5033
From : D V Larsen Phone:- 316-3256
International : (+2711) 316-3256
No. of Pages : 2
Your Reference :
Our Reference :



Dear Sirs,

THE NOISE IMPACT OF COOLING FANS AT APOLLO ON THE AMBIENT NOISE LEVELS AT THE PROPERTY OF MR DAVID LARSEN - Report number 3150/782102 dated September 1997

We thank you for your attention to this matter and refer to the above SABS report tabled by ESKOM at SALBU on 97/09/18. This report contradicts earlier findings and states we have no cause for complaint.

Based on information contained in the above SABS report, would the Chief Executive of ESKOM be prepared to give us an irrevocable undertaking that the cooling fans will be switched off should the noise propagation conditions, and therefore the level of the tonal noise from the Apollo DC cooling fans, exceed the "typical" conditions described by the measurements recorded in the SABS report ?

Should ESKOM be prepared to give us such an undertaking, we would like to discuss and agree methods of monitoring the level of the 33Hz and 66Hz tones from the 48x Apollo DC cooling fans.

We await your further advice with regard to the above and must again ask that the DC cooling fans remain off until the matter is resolved.

We remain of the opinion that the SABS report dated September 1997 contains some very valid information but that the CONCLUSIONS and RECOMMENDATIONS on page 5 of the report are both incomplete and misleading for the following reasons:-

The SABS report assumes that, on the night the measurements were taken, the meteorological conditions between our home and Apollo were "typical" when all of the evidence was to the contrary. The report makes no mention of the fact that under favourable atmospheric conditions sound waves are deflected upwards and can pass over a neighbouring property. Conversely under unfavourable conditions sound waves are deflected downward onto neighbouring properties. We would be prepared to accept the dB noise levels in this report if the author would concede that sound levels recorded could vary by as much as 25dB due to atmospheric condition and he would modify the report accordingly.

Typically the air movement during the winter months is from the south and not from the north as was the case on the night the SABS measurements were taken. We must assume that the Megawatts of heat blown upward by the Apollo DC cooling fans cause local inversion layer problems and other atmospheric disturbances that augment the general noise level on our property - the fans were OFF for long periods on the night in question and there was LITTLE or NO heat being moved into the atmosphere by the fans. Based on these assumptions the meteorological conditions between our home and Apollo were most certainly not "typical" as claimed in the SABS report.

The SABS report is based on measurements taken over a 24 hour period when the atmospheric conditions were such that we could not hear the "throbbing" noise that causes us distress - by our standards it was a quiet night - we made this VERY clear to the author of the report. We find it incongruous that this fact was not recorded and highlighted in the report. The report does however serve to record this "low" level of noise and states that the fan noise could not be heard by the SABS staff.

Our reference measurements taken on the same night inside one of the main house bedrooms at 22h00 were 10dB lower than the SABS measurement taken outside the cottage in the same time frame. On very noisy nights we measure indoor levels 25dB higher than our measurements taken on the night in question. The SABS measurements taken some years ago, as well as the earlier measurements made by Mr Verster Meij, confirm that the cooling fan noise does reach very high levels at our home.

Based on the measurements recorded in their report dated September 1997, the SABS concludes that the level of noise from Apollo was such there is "no cause for complaint". The SABS report refers only to the SABS code of practice when making this statement and does not refer to other accredited publications that deal with the impact of low frequency noise (LFN) on communities.

The SABS report records the presence of a single 33Hz tone from Apollo but does not highlight the fact that such tones will be present for each of the 48x 2.5 meter diameter fans at Apollo and that multiple beat notes will occur and will cause a complex random "throbbing" sound. The report does not acknowledge that prolonged exposure to VLF "throbbing" sounds, although masked by other noises, can be debilitating.

It should be noted that, according to the paper "Low Frequency Noise Annoyance Assessment by Low Frequency Noise Ratings by N Broner and HG Leventhall", even this "low" level of noise as recorded by the SABS on this "quiet night" is already above the level where complaints can be expected. (see SABS report page D-6 (A) Third-octave frequency 31.5Hz : sound pressure level 45dB (B) note the pronounced "15dB" increase in noise and the "33Hz peak" in the spectrum display when the Apollo cooling fans are switched on and off : there is no record of the number of fans that were switched on and off).

The SABS was given a copy of the Broner and Leventhall paper by ourselves. Based on the SABS measurements taken at our home the SABS report states that "there is not cause for complaint" - on what grounds does the SABS disregard the validity of the LFNR recommendations made by Broner and Leventhall that clearly indicate that we have cause for complaint even at the low level of noise recorded by the SABS on the night in question?

The health and well-being of our family is at stake and we must have an answer to the above question.

Please refer to the ESKOM letters dated 26th of November 1993 (ref TK550/15 - Mr KJ King) and the ESKOM letter dated 28th of May 1979 (ref Apollo/MOS - Mr MO Smith) assuring us that "ESKOM was doing everything in their power to study the problem in depth so that ways and means could be devised to ensure an acceptable solution" and that "the supplier had advanced proposals to change the fan blade profiles to reduce the noise and that this will be further discussed with him in 1994" this letter further assured us that "investigations were proceeding at a pace dictated by the total rehabilitation of the Cahora Bassa-Apollo system". (Mr KJ King's letter dated 26th November 1993 is attached)

As you are aware these letters were based on the ESKOM commissioned SABS measurements taken some years ago, as well as the earlier reports and the findings and measurements made by Mr Verster Meij (SABS retired) and others.

You are also aware that no action has yet been taken by ESKOM to reduce the noise radiated by the 48x 2.5 meter diameter cooling fans or to investigate the impact this cooling system has on the general environment and, in particular, the atmospheric environment in the immediate vicinity of Apollo.

Against this background I am sure that you must agree that the SABS report number 3150/782102 dated September 1997 is clearly incomplete and as such the CONCLUSION could be very misleading.

I must again ask that the Apollo DC system does not go online until this matter is resolved in terms of the undertakings given to us in the ESKOM letters dated 26th of November 1993 and ESKOM letter dated 28th of May 1979.

We look forward to an early reply,

Yours faithfully,

David Larsen



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