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Specified risk number one is flammable substances and oxygen enrichment. How could we have that sort of environment? Well, one with flammable substances, that can be just down to the materials inside. It could be certain dust, chemicals. It can even be down to a process. Such as, for example, somebody welding inside. We can also get oxygen-rich environment, again, due to oxygen levels increasing due to processes. The risk is real in many circumstances.

Let us now look at the way in which fire does actually develop. We are going to look at something known as the lower explosive limits and the upper explosive limits. If we were to use, for example, a lot of petrol, petrol burns very quickly. Its lower and upper is very small, between 1.5% and 7.5%. But in reality, if we have too much air or too many vapours, it is very difficult to ignite. It has to be something that we call the ideal mixture. Now, there are many gases that will reach their ideal mixture; gases that can be present in many confined spaces. Just to give you an example, methane, its low exposure limit is 5% but its upper is 15%. And that is the period in which it will ignite. Hydrogen sulfide, 4.3% to 45%. Carbon monoxide 12.5% to 74%. Acetylene is 2.4% to 83% and butane 1.5% to 8.5%. So everything at some point will reach its ideal mixture. That is when the potential for fire and explosion will occur.

Number two of our specified risks is excessive heat. High temperatures and high humidity will make the job both uncomfortable, but it will increase our core body temperature. Think of some of the examples: Steam pits, ovens, kilns. There are many working environments where heat can be a potential risk. What would be the effect on someone who is going to get hot? Well, heat exhaustion is the first one. The body starts to sweat profusely. Then they could easily end up going into heat stroke, where they might lose their strength and finally, heat syncope is when we lose total control of our body and usually go unconscious. So we have to be wary of working in hot temperatures.

Number three specified risk is toxic gas, fumes or vapours. Now at this point, we are going to look at a document known as an EH40. EH40 is produced by the Health and Safety Executive, and it falls under, what we call exposure limits and under COSHH Regulations. What this document does, it looks at a whole range of chemicals that affect the human body. And it breaks down to two-time scales. One is an eight hour period, long-term exposure, and 15 minutes which is short exposure. And what we are going to do is look at some examples of how some of these attack the human body. Now, this document is very important. We would use it in conjunction with your gas monitor. If that gas monitor was to go off, we know it will retain the readings, particularly, the peak reading that you have... You have inhaled a particular substance. That information is important when a person is sent to hospital so they can treat the person with the right medication or with oxygen therapy to remove that substance in them.

Let us look at some examples. Carbon dioxide, that is a colourless and odourless but non-combustible gas, which is heavier than air. You can imagine that would be low laying inside a vessel. It is both common in solid and compressed liquid forms, but we find it because it is part of organic decay. For example, grain elevators, sewers, storage bins and wells, we could find levels of carbon dioxide. It is even part of the fermentation process. Digesters, molasses pits, beer, and wine vats will contain carbon dioxide.

Another gas, that of carbon monoxide. Now, this is colourless and odourless, slightly lighter than air. Look at it like head gas, however, it is an asphyxiant, which means it will kill. With over a low dosage over a long period of time people have died. But in high concentration levels, death is very quick indeed. Now, its primary source is the incomplete combustion of organic material. For example, petrol fuel combustion engines give off carbon monoxide. Building fires give off carbon monoxide. Next, hydrogen sulfide. Known as sewer gas, smells like rotten eggs. The danger with this particular gas though, it has a very short odour threshold of 0.02 to 0.2 parts per million. The problem is, you become desensitized to the smell very quickly, and you could think that the gas is no longer present, but it is. Again, this is colourless and flammable and heavier than air. Just imagine you have walked over a manhole cover and you can smell it, that proves it is absolutely full.

Specified risk number four, which is oxygen deficiency. How can we have an oxygen-deficient atmosphere? Two ways: One, we do consume it, and two, we can displace it. Let us look at the consumption part. Now imagine somebody working inside a confined space where there is not much natural ventilation. As people breathe in and out, we are changing that atmosphere, and when we reach 19.5%, that is viewed as being oxygen-deficient. Currently, the oxygen levels around us are about 20.8%, so that is not a lot to go down to the point where we view it as being oxygen-deficient. But what effect will a lack of oxygen have on me and you? There will be some early signs and symptoms that we need to be aware of. The medical term is hypoxia. If I felt unwell if I have started to feel dizzy, if I had tingling sensations in my hands and feet if I started to go pale, blueness of the lips. They are all classic symptoms of hypoxia. Now, at this point, there is a general rule when anyone feels unwell in a confined space, "We all get out. Something is not right, we need to re-check our risk assessment and our method statements." What about the displacement? Well, the displacement may well be if we introduce something, for example, like welding. As a welder uses oxygen, it gives off some toxic gases, that would displace the oxygen inside that atmosphere.

Specified risk number five, the ingress or presence of liquids. A good example of this might be a culvert. Maybe you are doing some survey work or some repairs inside. We need to be aware of the fact that the water, while might, initially, be very low, something could occur upriver; flash floods, and suddenly, you see the water rise rapidly. There is a real risk someone could drown.

Specified risk number six, solid materials which can flow. What examples do we have here? Could be grains, dust, flour. There is a whole range of items that would fall under being a solid material but can actually flow. The danger here is, on many occasions, you cannot stand on this product. Unfortunately, people have actually died by entering into a silo and trying to stand on grain. And basically, they have sunk and died.