RSSB2751 - T1167 - WP2 - Testing the effectiveness of detonators - Tender Deadline Extended to January 4th 2019 12:00 Mid-Day

Detonators are small metal devices that contain a small quantity of explosives, that are placed on the railhead to cause a loud sound, activated by the wheel-rail interface of a passing train to alert the driver they are approaching a hazard on the line ahead (RSSB GE/GN8532, 2015). During track possessions, detonators are intended to provide a safety protection method if for example a train has been incorrectly signalled into a worksite or to mitigate unauthorised engineering trains exiting the worksite.

For detonators to be effective, they must be clearly audible so necessary precaution and mitigation action can be taken. The Rail Group Standard GM/RT2160 (RSSB, 2010) mandates the requirements for the audibility of detonators in driving cabs, and states that:

"Driving cabs shall have acoustic characteristics that ensure that exploding detonators, as specified in BR 0640A, can be heard inside the cab at any vehicle speed and readily distinguished from background noise" (p. 5).

In a live running railway, it is expected there are a variety of circumstances that will affect the audibility of detonators. T315 workstream 1: noise exposure of staff in driving cabs (RSSB, 2004) suggest sources of driving cab noise include rolling noise, traction and ancillary equipment noise, aerodynamic noise, warning horns, in-cab audible warnings, air-conditioning equipment and heater fans. These, and other factors such as environmental conditions (e.g. weather), insulation of the cab, and subjective comfort, may influence the extent in which detonators are audible to the driver.

Detonators that are not clearly audible to the driver may exacerbate safety risks, if they are not alerted to a hazard or possession on the line ahead. T326 Good Practice Guide for the design of alarms and alerts (RSSB, 2008) note that warning alarms must be heard against background noise but should not exceed noise tolerance limits. Ambient noise should be no greater than 85dB(A) for any length of time, and alarms should be between 15 and 25dB(A) above the ambient noise, which in total, should not generally exceed about 110dB(A). As detonators provide a warning alert that is activated externally to the cab, given variable factors that may influence the audibility of detonators, it is unknown in what conditions detonators are clearly audible to the driver.

It is also possible that audibility of detonator activation may alert track workers of an approaching train. The extent in which detonators may be audible to track workers is likely to vary depending on conditions such as distance of working from detonator placement, weather, personal protective equipment (ear protection) and machinery in use. However, little evidence is currently available to determine whether detonators provide such secondary function, and what, if any, conditions may influence their effectiveness in being audible to track workers.