“oxygen enrichment may occur from leaking gases, welding equipment, or oxygen lines that have not been blanked”
According to Canada’s Ontario Ministry of Labor: “If the concentration of oxygen falls below the acceptable limit of 19.5%, the space is oxygen-deficient. This hazard is a significant cause of many fatalities in confined spaces. Oxygen deficiency may occur from biological or chemical reactions such as rusting, or by displacement of oxygen by other gases.”2 Doctors typically refer to two distinct forms of oxygen deprivation: anoxic brain injuries occur when the brain is totally deprived of oxygen due to sudden cardiac arrest, choking, strangulation, and other sudden injuries. Hypoxic brain injuries occur when the brain receives less oxygen than it needs, but is not completely deprived of oxygen.
Hypoxic brain injuries are the type of brain injury that typically occurs in a confined space injury. You may lose consciousness after between only 30 to 180 seconds of oxygen deprivation, which means, in practical terms, you must have all the appropriate rescue equipment in place before the oxygen levels drop below the appropriate concentration. Some of you reading this may be jumping to the erroneous conclusion that a respirator or self-contained oxygen breathing apparatus might offer universal protection in a confined space, obviating the need for someone outside the confined space to monitor the air inside. Unfortunately, too much oxygen can also be a problem. “If the concentration exceeds the limit of 23%, then the space is oxygenenriched, increasing the likelihood of explosions or fires by increasing the potential of any combustible or flammable material to be ignited as well as the rate of reaction. Oxygen enrichment may occur from leaking gases, welding equipment, or oxygen lines that have not been blanked.”3 So it is important to maintain oxygen levels of 20%–22% oxygen and this is impossible to do without appropriate gas monitoring by a qualified individual using recently calibrated equipment and gas detectors.
Oxygen enriched confined space makes an explosion or fire more likely. While a source of self-contained breathing apparatus might be a good precaution against oxygen deficiency, it is dangerous to be wearing one during a fire or explosion in a confined space, so irrespective of whether or not the worker in a confined space has a respirator, continuously monitoring the air quality in the confined space is essential.
While oxygen levels are important, they are not the only atmospheric condition to be considered. Last summer I was walking down to the local chemist when I saw a man working in a confined space alone. He was in a pit working on a highly pressurised waterline. He was up to his knees in water and if the line had broken, which was certainly a strong possibility, he would probably have drowned before he would be able to vacate this one meter pit accessible only by a rickety ladder. There was no-one outside the pit monitoring the air and no-one to even call for assistance should tragedy befall him. I called him out of the pit and explained the dangers to him (yes, safety has destroyed my life. Before I knew about these dangers I could walk by without noticing and certainly with no moral compunction that would force me to intervene) to which he replied that his supervisor told him to do it this way.
When I asked where I could find his supervisor he pointed to the next corner where I found the supervisor performing the same job on a different pipe but in the exact same manner. He told me that he was understaffed and this was the only way it could be done. I called the company and told them I wanted to speak to the head of safety (there was no one local this being a Canadian firm and me being in the US.) I called OSHA and went on my way, it was clear that nothing I could say or do was going to save these two sods from themselves. Fortunately, on my way home work had been suspended and the company was replaced by one more safety conscious the next day. I don’t know if I had anything to do with it, but since there is no proof that I did not, I am taking credit for saving those men until someone comes out with irrefutable evidence that I did not.
Explosive or toxic gases
Another common problem in confined spaces is the presence of explosive or toxic gases. Sometimes operations like cutting or welding release gases that either reduce the amount of oxygen in the air or are in themselves toxic or explosive. Welding and cutting can release shielding gases such as carbon dioxide, argon, helium; fuel gases such as acetylene, propane, butane; and oxygen, which is used with fuel gases and also in small amounts in some shielding gas mixtures. So again, it is essential not only to continuously monitor the atmosphere, but also to use gas detectors to guard against the build up of explosive gases in the proximity of an open flame.
“maintaining oxygen levels of 20%–22% is impossible to do without appropriate gas monitoring”
While work processes like welding and cutting can create toxic or explosive gases, or gases that will displace oxygen making the ambient air unbreathable, they are not the only sources of dangerous gases. In some operations, particularly in agriculture, decomposition of natural materials can create carbon dioxide and hydrogen sulphide, a gas so toxic that in high concentrations inhalation of it leads to almost instantaneous death4. And in a confined space like a silo the likelihood of toxic gases accumulating into highly concentrated amounts is relatively high.
Another process that occurs deliberately or accidentally and produces toxic gases is fermentation. The fermentation process can produce hydrogen, ethanol, acetone, and of course carbon dioxide. Again, depending on the amount of time the substance has been fermenting and the size of the confined space the gases could range from causing illnesses to becoming fatal.
Although we tend to think of physical structures like access tunnels and storage tanks when we discuss confined spaces, it is possible to have temporary structures that fit the broad definition of a permit to work. One example of such a structure is a trench dug during construction. Far too often trenches collapse and trap workers who suffocate under the heavy loads of earth that cover them in a cave in. Workers being trapped in trenches that either collapse or that are rapidly filled with water during a flash flood are the leading causes of fatalities in some parts of the world. This increased risk of fatality is caused primarily either because the trench was poorly constructed and did not consider the need for workers to rapidly evacuate the trench, and/or because there was a near complete lack of any sort of emergency response plan.
Confined space planning
The speed at which hazards in a confined space can lead to death or irreversible injury, coupled with the difficulty in rescuing a worker exposed to these hazards, makes preparation and planning the single best way of protecting workers who access confined spaces. Most companies working in a confined space require (many times by law) a confined space permit.
The elements of a confined space permit to work will differ slightly from location to location, but in general a confined space permit will include:
The time the worker(s) enter and exit the confined space
The results of atmospheric testing
A list of emergency response equipment on hand
A list of all required Personal Protective Equipment (PPE)
A list of all known hazards and associated actions necessary to reduce the risk of injury
Emergency response numbers and personnel
Ideally the confined work permit would be accompanied by a safety plan, a safety risk assessment, and an emergency response plan.