HYPERBARIC TUNNELING SUPPORT
ASI is proud to be the first Canadian company to provide Hyperbaric Tunneling Support Services to Tunneling companies in North America. These services include consultation for all hyperbaric needs (planning, risk assessment, safety and adherence to local regulatory requirements), hyperbaric intervention support, hyperbaric worker training, equipment maintenance program and servicing of the air-lock and supporting systems. In 2014, ASI has successfully completed over 70 hyperbaric interventions and is currently working with SNC Lavalin SELI (SSJV) on the Evergreen Tunnel project in British Columbia. Below provides further insight into Hyperbaric Tunneling Support. If you are interested in this service, please contact Scott Black, Sr. Operations Manager Commercial Diving & Tunneling Support.
What happens when an earth pressure balance (EPB) tunnel boring machine (TBM) breaks down in the middle of a project while surrounded by tonnes of earth?
That’s when your Hyperbaric Tunneling Support team gets called in. They are also required to be on-site during various stages of the tunneling project. These highly trained individuals are unique in their abilities. Trained to perform construction, repair and inspection work in physical high pressure environments (underwater), the hyperbaric tunneling support team are those who can support you immediate needs to help get your TBM up and running after a breakdown, avoiding further project delays.
Why can’t construction workers or maintenance staff take on this task?
The EPB, TBM is a machine developed to operate in a pressure environment in order to combat against the natural pressures of the earth of which it is being drilled into. Air pressure is introduced to the front working chamber of the TBM slightly higher than the surrounding ground pressure, this pressurized space allows workers a safe environment to work and or perform planned and un-planned inspections, cleaning and repair requirements on the cutting head of the TBM. Because this space contains air pressure at a higher atmospheric pressure than we are accustomed on the surface of the earth (1.013 bar/absolute), workers who work within this space must be trained and aware of the physical risks involved with working in high pressure environments (>1.013 bar). Safety requirements for this type of work environment include having a hyperbaric decompression chamber (emergency shuttle) on-site along with emergency medical staff and written evacuation procedures.
Air Lock Chamber
The process of passing personnel/workers from a regular atmospheric environment to a pressurized space requires an air lock system/chamber for the equalization of the differential air pressures. This air lock system is fitted to the very front of the TBM, allowing access to the working chamber. The procedure requires individuals to enter into the air lock chamber where 2 sets of sealing doors are built in at opposite sides. Once entered into the air lock chamber, the doors are closed and pressurized air is pushed into the air lock until the air pressure matches the air pressure outside the machine. Once the pressures are matched (equalized), the second set of doors can be opened and the individuals can crawl out into the working chamber and begin performing their assigned duties.
Working in high pressurized environments
All trained hyperbaric tunneling support team members and workers can only work a certain amount of time under pressure before they are required to decompress (the same as diving underwater). The amount of time is dependent on the actual working chamber air pressure and assigned ‘Decompression Table’ for the intervention. For example, if an individual is working in an environment comparable to 40fsw (feet of sea water), they can only work for 2.5 hours in accordance with the Canadian DCIEM Diving Table. Any work performed in excess of this time would require planned decompression before the workers can safely exit the air lock to our regular atmospheric environment of (1.013 bar/absolute). Failing to do so can result in Decompression Sickness.