Hazardous Atmosphere in Sewers
Important Information About VOC's In Melbourne's Sewer Network
In 2014, Melbourne Water undertook research into hazardous atmospheres in sewers and has identified the presence of Volatile Organic Compounds (VOC’s) in Melbourne’s sewer network. As a result, most Victorian water authorities including Melbourne Water, Yarra Valley and South East Water now require that anyone coming into contact with sewer headspace gas to have in addition to their traditional four gas sensors, a VOC sensor and an ammonia sensor as part of their gas detection equipment.
What are VOCs and what is Ammonia?
- 209 Entries
- 37 VOC readings of over 10 ppm (Melbourne Water set their alarms for VOC at 10 ppm)
- 11 VOC readings of over 100 ppm
- The highest reading was 776 ppm
- Only 3 of these readings also exceeded the alarm for one of the standard four gases e.g. without the photoionisation detector (PID) only three of these events would have been detected
Changes in Melbourne Water's Confined Space Entry Atmospheric Monitoring Requirements
As a result of the results collected from the study conducted, Melbourne water has changed the confined space entry atmospheric monitoring requirements for sewerage transfer work. Melbourne Water now require that anyone coming into contact with sewer headspace gas have a Volatile Organic Compound (VOC) sensor and an ammonia sensor as part of their gas detection equipment. These two sensors are in addition to the traditional four gas sensors required for sewer entry. See below table. Similarly, other water authorities such as Yarra Valley Water and South East Water have also issued similar changes to their requirements for confined entry in sewer networks.
|Sensors Required||Low Alarm||High Alarm|
|LEL (Lower Explosive Limit)||5%||10%|
|CO (Carbon Monoxide)||30 ppm||35 ppm|
|H2S (Hydrogen Sulphide)||10 ppm||15 ppm|
|NH3 (Ammonia)||15 ppm||25 ppm|
|VOC (Volatile Organic Compounds via a PID)||10 ppm||20 ppm|
Table 1. Sensors and alarm limits for entry into MW's Sewers
Air-Met Scientific encourages all parties who enter the sewer network to contact the specific water authority to ensure that they are equipped with the correct safety equipment and meet the relevant safety requirements for confined space entry in sewers.