In the last week of May, the Delhi Vidyut Board (DVB) came out with an advertisement in a leading daily, giving a 90-day notice to diesel generator users to ``renew the permission granted for DG sets and furnish additional information and certificates to the Delhi Vidyut Board''. The reason cited was: ``For effective pollution control, DVB has modified its requirements in respect of noise and air pollution control norms.''

The norms are a new addition to forms granting permission to operate DG sets to the Capital's users, amajority of whom are industrialists. Permission is required only for gensets with a generating capacity of 10 kv or above. Thus, most household users are ruled out.

``The new norms have been incorporated because the government has realised that generators are one of the biggest culprits in causing pollution. Even the Supreme Court observed in a notice last year that over 40 per cent of the pollution in the National Capital Region is caused by diesel generators. There is a PIL pending in the High Court against generators. Therefore, the stipulation by the Delhi Vidyut Board is a welcome move,'' says Dr Chander Prakash, senior environmental engineer, Delhi Pollution Control Committee.To curb air pollution, the board has focussed on the height of the stack (chimney) in each generator, in proportion to the building where it is installed. Therefore, minimum height of the stack can be worked out by using the following formula: H = h + 0.2/kva. Here, `H' is the total height of the stack in metres, `h' is theheight of the building where the generator set is installed and `kva' is its total generation capacity.

So for various generating capacities of up to 300 kva, the height of the chimney can be calculated. The stack height is checked by a board engineer before granting permission to the consumer.

Another certification is required in terms of air pollution from the manufacturers. The user has to submit a document from the maker certifying that the DG set does not contain dust particles of 150 mg/Nmg at the time of the application for permission. For noise control, the board has prescribed limits in four classes: industrial area, commercial area, residential area and silent zone (eg. hospitals). The range of noise for these are between 70-75 dba, 55-65 dba, 45-55 dba and 40-50 dba respectively. The upper limit specifies the noise permissible during the day and the lower limit, the decibels permissible at night.

At the point of manufacture, the noise level has to be maintained between 85-90 dba at a distanceof one metre from the diesel generator. If the noise is beyond the permissible limits, it can be controlled by using an exhaust or a muffler or providing an acoustic enclosure.