DEEP BORE Tunneling Projects â Decompression Injury Management
DEEP BORE Tunneling Projects -- Decompression Injury Management
I usually do not write about medical issues in this blog. However, this is a great article about decompression injuries and some considerations related to these projects. This is an excerpt of a longer article which is found at Hamilton RW, Kay E. Boring Deep Tunnels. In: Proceedings, Third Conference of U.S.-Japan Panel on Aerospace-Diving Physiology & Technology, and Hyperbaric Medicine. 2008 November. Nakatsu, Japan.
Deep Boring Projects. Firefighters who manage injuries deep underground, this decompression issue should be at the forefront of your differential diagnosis and treatment for the injured worker. In many cities across the United States, the process of digging tunnels deep underground has changed in the last three decades, due largely to the Tunnel Boring Machine (TBM). This has revolutionized the compressed air mining and tunneling industry, creating a whole new world for the emergency responder. The TBM consists of a circular, rotating, cutting head or face, which may be from 5 to more than 10 metres in diameter. This is pushed forward as it cuts, while a tunnel is cemented behind it. The modern pressure-shielded TBM allows compressed air workers to work most of the time in a relatively safe one-atmosphere environment behind the face. Occasional excursions (interventions) into the pressurized head space through a man-lock are performed to service the cutter head. These interventions may involve only two or three workers at a time and may last minutes to a few hours, in sharp contrast to the traditional “sand hog” operation where dozens of workers worked shifts as long as could be managed within a normal work day. Tunnel and caisson work in the old days involved hordes of sandhogs, digging with the muscles of their shoulders and backs. The image that should come to mind is that of the Brooklyn Bridge, which left its engineer a cripple due to decompression issues. Decompression is still a major factor in tunnel and caisson work.
Categorically, compressed air environment work has caused a lot of injury. Digging was being done using remotely controlled tools. Workers only entered the caisson pressure when repair was needed. Workers had to enter pressure only when something went wrong or changes were needed. There were few workers under pressure, but because of archaic rules they still had to decompress in many cases without benefit of oxygen.
Another fundamental new development is the extensive use of oxygen. Oxygen breathing on the job site is limited in some international jurisdictions, but there is no doubt that oxygen can greatly improve both the speed and the reliability of decompression and its use requires following well-established safety procedures. Tunnel Boring Machine depths may exceed the narcotic limits for effective work using air as a breathing gas, so TBM operators may use breathing mixtures containing non-narcotic helium. Wide experience with such mixtures in deep sea diving is finding its way into tunneling practice. Modern TBM techniques allow work at pressures much greater than those considered normal for traditional compressed air methods, and as a result the rules and requirements may not be appropriate.
It is generally not necessary to tell workers and first responders about the benefits of breathing oxygen during decompression. Oxygen makes decompression a great deal more reliable—“safer” if one wants to use that term—with far less decompression sickness and the subtle subclinical disturbances that may have lasting effects but that seldom get treated. Among these decompression disorders is aseptic bone necrosis, also known as dysbaric osteonecrosis since it is caused by changes in pressure. Decompression with oxygen is much faster and therefore less expensive. In the USA not only is oxygen not allowed, but the decompression tables required by the Occupational Safety and Health Administration are not at all adequate at the higher pressures, leading to substantial incidents of dysbaric osteonecrosis on the workers and quite possibly the rescuers.
Oxygen is not without its price. For one, there is the fire risk, which is the main reason oxygen has been prohibited. But compressed air alone, even without extra oxygen, increases the fire risk; this is well known in the compressed air community. Dealing with oxygen requires proper training, an overboard dump system for the breathing masks, and continuous on-line oxygen analysis in order to make it safe. Even long exposures to continuous oxygen can create lung
Many individual factors affect the susceptibility of an individual to decompression sickness. One main factor is acclimatization. Compressed air workers who have been exposed regularly are more tolerant of decompression. In Navy diving this is called “work up.” It has been found to be a major factor in both tolerances of compressed air exposures and of dives. On some deep bore and caisson jobs there is the use of helium as “trimix”. Helium has been used as a component of deep sea divers’ breathing gas in commercial and in military diving for well over half a century. There are two main reasons: Helium is lighter and easier to breathe, but its main benefit is that it does not cause narcosis. While a diver can do simple work while breathing air at pressures up to 7 or so bars, at greater than about 4 bars memory and the ability to do detailed work or multi-tasking can be severely impaired. In recent years high-end recreational divers have begun using helium to reduce narcosis in the form of an oxygen-helium-nitrogen “trimix” for diving beyond about 4 bars.
On a job and when an intervention is needed a team of 2 or 3 workers transfers into a “man lock” which is in the corner of the machine room. The lock is pressurized to the pressure of the machine room and the workers transfer through the lock into the machine room. Sometimes the intervention is to do work on the machinery, but when work in front of the face is needed the team enters the face area through a door in the face. They may be wet, but with this arrangement they are normally not totally immersed. Once work is complete the workers transfer back into the machine room, where they clean off and transfer into the man lock. The hatch is sealed and they begin the proper decompression profile for their exposure.
What does this mean to the first responder? First it is IMPERATIVE that the fire department is on the front end of the emergency response plan for these projects. Second, going in after injured workers requires and intense pre-training period and equipment. It is important that if your department is asked to be the first responder for illness or accidents at these Deep Bore projects that the lead engineering or contractor organization provides adequate money, resource and equipment for your departments training and response. You may be asking for over one hundred thousand dollars to put this all together depending on the depth and duration of the project as this is a super confined space response. Look to other departments for technical assistance. Do not sign on as the first responder without the adequate resources required for these rescue efforts. There must be daily training to become familiar with the equipment, the depth the challenges the construction staff and you may see if there is a medical specialist available to assist in the response and the training. It is equally important to know where your closest hyperbaric chamber is located and their availability; for example 24 hour availability. Here in the Seattle area there are a few chambers located at the hospitals and at the Navy base. ARE there similar resources close to your agency?
This challenge is an interesting twist in emergency service response and what we may be called on to manage. It’s important that we are well trained and prepared or we may find ourselves in the decompression chamber as well as your patient.
I usually do not write about medical issues in this blog. However, this is a great article about decompression injuries and some considerations related to these projects. This is an excerpt of a longer article which is found at Hamilton RW, Kay E. Boring Deep Tunnels. In: Proceedings, Third Conference of U.S.-Japan Panel on Aerospace-Diving Physiology & Technology, and Hyperbaric Medicine. 2008 November. Nakatsu, Japan.
Deep Boring Projects. Firefighters who manage injuries deep underground, this decompression issue should be at the forefront of your differential diagnosis and treatment for the injured worker. In many cities across the United States, the process of digging tunnels deep underground has changed in the last three decades, due largely to the Tunnel Boring Machine (TBM). This has revolutionized the compressed air mining and tunneling industry, creating a whole new world for the emergency responder. The TBM consists of a circular, rotating, cutting head or face, which may be from 5 to more than 10 metres in diameter. This is pushed forward as it cuts, while a tunnel is cemented behind it. The modern pressure-shielded TBM allows compressed air workers to work most of the time in a relatively safe one-atmosphere environment behind the face. Occasional excursions (interventions) into the pressurized head space through a man-lock are performed to service the cutter head. These interventions may involve only two or three workers at a time and may last minutes to a few hours, in sharp contrast to the traditional “sand hog” operation where dozens of workers worked shifts as long as could be managed within a normal work day. Tunnel and caisson work in the old days involved hordes of sandhogs, digging with the muscles of their shoulders and backs. The image that should come to mind is that of the Brooklyn Bridge, which left its engineer a cripple due to decompression issues. Decompression is still a major factor in tunnel and caisson work.
Categorically, compressed air environment work has caused a lot of injury. Digging was being done using remotely controlled tools. Workers only entered the caisson pressure when repair was needed. Workers had to enter pressure only when something went wrong or changes were needed. There were few workers under pressure, but because of archaic rules they still had to decompress in many cases without benefit of oxygen.
Another fundamental new development is the extensive use of oxygen. Oxygen breathing on the job site is limited in some international jurisdictions, but there is no doubt that oxygen can greatly improve both the speed and the reliability of decompression and its use requires following well-established safety procedures. Tunnel Boring Machine depths may exceed the narcotic limits for effective work using air as a breathing gas, so TBM operators may use breathing mixtures containing non-narcotic helium. Wide experience with such mixtures in deep sea diving is finding its way into tunneling practice. Modern TBM techniques allow work at pressures much greater than those considered normal for traditional compressed air methods, and as a result the rules and requirements may not be appropriate.
It is generally not necessary to tell workers and first responders about the benefits of breathing oxygen during decompression. Oxygen makes decompression a great deal more reliable—“safer” if one wants to use that term—with far less decompression sickness and the subtle subclinical disturbances that may have lasting effects but that seldom get treated. Among these decompression disorders is aseptic bone necrosis, also known as dysbaric osteonecrosis since it is caused by changes in pressure. Decompression with oxygen is much faster and therefore less expensive. In the USA not only is oxygen not allowed, but the decompression tables required by the Occupational Safety and Health Administration are not at all adequate at the higher pressures, leading to substantial incidents of dysbaric osteonecrosis on the workers and quite possibly the rescuers.
Oxygen is not without its price. For one, there is the fire risk, which is the main reason oxygen has been prohibited. But compressed air alone, even without extra oxygen, increases the fire risk; this is well known in the compressed air community. Dealing with oxygen requires proper training, an overboard dump system for the breathing masks, and continuous on-line oxygen analysis in order to make it safe. Even long exposures to continuous oxygen can create lung
Many individual factors affect the susceptibility of an individual to decompression sickness. One main factor is acclimatization. Compressed air workers who have been exposed regularly are more tolerant of decompression. In Navy diving this is called “work up.” It has been found to be a major factor in both tolerances of compressed air exposures and of dives. On some deep bore and caisson jobs there is the use of helium as “trimix”. Helium has been used as a component of deep sea divers’ breathing gas in commercial and in military diving for well over half a century. There are two main reasons: Helium is lighter and easier to breathe, but its main benefit is that it does not cause narcosis. While a diver can do simple work while breathing air at pressures up to 7 or so bars, at greater than about 4 bars memory and the ability to do detailed work or multi-tasking can be severely impaired. In recent years high-end recreational divers have begun using helium to reduce narcosis in the form of an oxygen-helium-nitrogen “trimix” for diving beyond about 4 bars.
On a job and when an intervention is needed a team of 2 or 3 workers transfers into a “man lock” which is in the corner of the machine room. The lock is pressurized to the pressure of the machine room and the workers transfer through the lock into the machine room. Sometimes the intervention is to do work on the machinery, but when work in front of the face is needed the team enters the face area through a door in the face. They may be wet, but with this arrangement they are normally not totally immersed. Once work is complete the workers transfer back into the machine room, where they clean off and transfer into the man lock. The hatch is sealed and they begin the proper decompression profile for their exposure.
What does this mean to the first responder? First it is IMPERATIVE that the fire department is on the front end of the emergency response plan for these projects. Second, going in after injured workers requires and intense pre-training period and equipment. It is important that if your department is asked to be the first responder for illness or accidents at these Deep Bore projects that the lead engineering or contractor organization provides adequate money, resource and equipment for your departments training and response. You may be asking for over one hundred thousand dollars to put this all together depending on the depth and duration of the project as this is a super confined space response. Look to other departments for technical assistance. Do not sign on as the first responder without the adequate resources required for these rescue efforts. There must be daily training to become familiar with the equipment, the depth the challenges the construction staff and you may see if there is a medical specialist available to assist in the response and the training. It is equally important to know where your closest hyperbaric chamber is located and their availability; for example 24 hour availability. Here in the Seattle area there are a few chambers located at the hospitals and at the Navy base. ARE there similar resources close to your agency?
This challenge is an interesting twist in emergency service response and what we may be called on to manage. It’s important that we are well trained and prepared or we may find ourselves in the decompression chamber as well as your patient.
