Singapore legislation
Regulation 86
of Workplace Safety and Health (Construction) Regulations 2007
Regulation 86
Means of communications
Subregulation 1
Effective and reliable means of communication, such as a telephone network, shall be provided at intervals of 100 metres along the tunnel in the worksite, including outside the portal or at the top of the shaft, and maintained at all times.
Subregulation 2
Any code of audio and visual signals used shall be conspicuously displayed near the entrances to the worksite and such other locations as may be necessary to bring it to the attention of all persons concerned.