April 2011 in Train Operations
The loud volume of the Automatic Warning System (AWS) apparatus on some of the Class 150, 153 and 170 units concerns one reporter.
The issue of the volume of the AWS bell and horn on these units has been raised numerous times through company channels. However, the response normally is that the volume is within the limits of 90-95 decibels set by the Railway Group Standard. The reporter states that the volume of the bell and horn are not only distracting whilst in the cab but also cause headaches for the staff driving the affected units. Concern has also been expressed about the possible long term consequences of being exposed to this level of noise. It is thought that some staff are placing objects into the speaker to reduce the noise.
The reporter has read reports that state noise in the work place that is intermittent should be no higher than 87 decibels. This contradicts the level set in the Railway Group Standard.
Could the RSSB:
The requirements for audibility of AWS in cabs are set out in a Railway Group Standard GE/RT8035 which covers all types of rail vehicles. It is clearly important that the AWS signal is heard in the cab of the vehicle so that the Driver can react appropriately. Where the cab has a higher level of background noise, then minimum levels of audibility have to be achieved and the standard addresses such circumstances.
With more modern types of rolling stock, cab background noise has been reduced and therefore the minimum levels for AWS audibility levels may be high. A number of successful derogations have been submitted to lower the minimum levels to set a value above the measured background noise, to maintain audibility, but which is lower than the standard mandated in GE/RT8035.
As part of standards project 10/053, the intention is to amend the AWS Railway Group Standard GE/RT8035 to reduce the specified volume of the AWS audible warnings. It is currently anticipated that the revised standard will be published before the end of 2011. It is proposed that the revised standard will require that the audible warnings shall have a sound level at least 10 dBA (the A weighting in noise measurements) above the expected ambient noise level in the cab, with a minimum of 65 dBA and a maximum of 95 dBA. These requirements are, however, subject to consultation and review by the appropriate Standards Committees.
A number of derogations have been granted to permit reduced volume levels. However, the majority of these apply to Electrical Multiple Units (EMUs), although 06/146/DGN granted to South West Trains also includes Diesel Multiple Units (DMUs) (classes 158 and 159).