Presented by: Dr Ross Di Corleto, the Principal Advisor – Health Risk for a large global mining group and author of blog The Thermal Environment.
Run time: 45:16
Download a copy of this podcast (MP3, 21 MB)
Construction Work Health Forum Podcast
Presented by: Dr Ross Di Corleto
START OF TRANSCRIPT
Okay, so what I want to do is go through a couple of areas. I'm going to introduce you to the basic concepts of heat stress. Now the reason I do that is just to give you some background as we start to go into some of the other key aspects of how it affects the body and what we do to control it. You need to get a feel for these basic concepts. How the human body reacts? If we know how the human body reacts, then we've got some ideas of how to anticipate we've got an issue and how to teach people and how to control it. Very briefly, I'll talk about heat illnesses; the classics. Then we'll do a little bit on myth busting. There's a lot of myths out there about heat stress and heat illnesses and hydration and all sorts of wonderful things, so we'll just touch on that one very quickly. Then how the environment is assessed; how do you determine whether we've got a heat stress issue? What are the key things that we look at? Then to finish off, what I want to do is actually do some practical exercises. So I've developed some scenarios and some of them – well, they're actual scenarios and we're going to assess them as a group and sort of get a feel for how we do it.
So first thing I think you need to be aware of is that there is a definition [long pause] – very fine line between heat stress and heat strain. Often it's used interchangeably. They're actually two different things. Heat stress is what we get from the environment; the heat and the humidity [long pause] and the workload. The harder we work, the more the body generates heat. So that's another heat stress. The clothing you wear; whether you're wearing light clothing or whether you're wearing a lot of PPE. Finally, individually or combined, they create heat stress for the worker. Right? So they're the things that impact and create heat stress. Heat strain is how the body reacts. So when you're body's under heat strain, you sweat, your heart rate increases. There's an elevated core temperature. So your body itself starts to increase in temperature and that's when we start to see issues. So the heat stress is the environment and the work area and the heat strain is how the body reacts to that.
So the other thing to bear in mind; on many occasions, I've had guys come up to me waving a thermometer under my nose and saying what temperature do we stop working? Well I wish it was that simple. But you'll see shortly that it's not quite that simple. There are so many factors that impact on heat. Yes, there's a temperature. But there's also the humidity. High humidity is worse than low humidity. Air movement; have we got good air movement in the area? Radiant temperature of surroundings. The air temperature mightn't be too bad, but if you're working in front of a furnace or you're working on top of a roof laying sheeting, you've got radiant heat coming up. That's another source you need to look at. What about clothing? We mentioned that before. What are you wearing? That's going to – the insulation factor, if it's a radiant heat, you need a little bit more. If you need to get air circulation, it may be you want something that's a bit more loose fitting. Of course, physical activity; the harder you're working, the more you're generating heat within the body. You need to look at that as well. So there are a number of factors you have to consider.
Then what about the individual themselves? How old are they? What's their general health? Weight and physical fitness? Hydration state? What have they been doing the night before? Have they had a few bevvies the night before and they're coming in to work already dehydrated? So they need to look at that. Acclimatise; have they just spent the last two weeks skiing in Queenstown and now you're going to put them into a hot site? That impacts on how they're going to cope. Finally, drugs. Now this is both illicit drugs and also prescription drugs. They all can impact on how the individual copes with the heat.
This slide, I think, is very important for the construction industry. When we talk about heat stress, people tend to think about – well, what do you think about if I say someone's suffering from heat stress? [Long pause] what comes to mind? [Long pause] yep. But what sort of impact on the individual would you expect?
Dizzy, yeah, tired, yep, headaches, cramps, collapsing. Now when we get to that stage, we've gone too far. The impact of heat stress really starts down here. The initial symptoms of heat stress are fatigue and lethargy. You know you get those hot days and they're humid and you really don't feel like doing anything. You're really worn out and tired. They're the initial stages that are starting to impact on the body. As it gets worse, within the workforce, we get decreased performance and lower productivity. It really does start to impact. If it continues that we don't put in any controls, we start to see an increased rate of mistakes and accidents. There are numerous studies out there that show that there is significant increase in accidents and safety incidents as the temperature gets hotter in the climate. So they're things you need to be aware of. People don't focus as well. Getting that spanner onto that nut is not quite as easy to do. Or swinging the hammer; they don't quite hit that on the spot every time as they start to stress with heat.
So not only does it impact – I mean, if you don't look after it, you then end up up the top. This is where we hear – we see the heat disorders. The cramps and the collapsing and all those sorts of things. They're the classical symptoms. But as I said, if you reach that point, you've left it too late. This is where you should be addressing it; down here. That will impact – it will be a lot easier to control and it's going to have a more significant impact on productivity.
Just some quick slides on the body, how it works. Very cleverly designed, our body. Operates at around about 37°C. That's core temperature inside. Okay? First symptoms of heat strain probably around about 37 to 39 core temperature. Heat stroke can occur at 40 degrees. Greater than or equal to. Death can occur at 42 and up. So between a perfectly healthy body and the potential for death, you're looking at five degrees core temperature. That's not a lot in certain conditions. Luckily, our bodies have been pretty well designed.
The other thing to bear in mind and people often forget is that as you work, you generate heat within the body. So not only are we talking about the environment that we're working in, but also how hard we're working. Because the harder we work, the more heat we generate and we have to dissipate or get rid of that heat in some way. So let's have a look.
How do we do it? The body is being – if you look at it similar to as you would a car engine. When the car engine is working, obviously the bonnet gets hot, the engine gets hot. It generates heat. So we have a cooling system in the car. Okay? So we have water in the car engine to help dissipate the heat. What have we got in the body? [Long pause] blood. Right? So we've got blood in the body, water in the car engine. In the car, we have a thermostat. In the body, we have a thing called a hypothalamus which acts as a thermostat. In the car, we also have a radiator. In the body, we have our skin. That's our radiator. In the car, we have a water pump. What's our water pump? [Long pause] our heart. Exactly. So they both work the same way.
So we're out there in the heat. Let's just say a moderate day. Let's say it's about 30 degrees out there. We're doing a bit of work. We're generating some heat. Our hypothalamus or our internal thermocouple kicks in and says it's getting too warm. So it sends a signal to the heart, which says you've got to pump a bit harder. So it pumps the blood to the skin. When it gets the skin, our blood vessels dilate. They increase in size. That's why often you see that red flushed look of people when they're hot. Blood vessels are increasing in size, higher surface area, so you can get more blood closer to the surface. Then what happens there is it loses heat to the environment. Because it's 30 degrees, our body's at about 37, 38. So it cools the skin which cools the blood which is pumped back the core and it cools the body. So very similar to a car. Right? Pumps the water to the radiator. The radiator evaporates the moisture which then goes on and cools the engine itself.
But what happens if we go through the same process – right? Hot, work, increase in the blood – and sends it to the skin. But what happens if our temperature out there is 38 degrees? We can't lose heat to the environment. So what does the body do? [Long pause] it sweats. As we sweat, we get a layer of moisture on the skin. That evaporates and that has a cooling effect. That's the body's key mechanism for cooling. Sweating is very, very important. Hence, the process of the air passing over the skin evaporating the sweat cools it. It's a very, very common system. How many of you in the room remember the old canvas bag on the front of the utes? That wasn't for decoration. That was very practical. As the car moves along, the moisture from the canvas bag evaporates and it cools the contents. The old bush fridge works on the same principle. You wet the canvas on the outside; it evaporates and cools the contents. Exactly the same thing happens with the body. You sweat, it evaporates, it cools the body. So they're things to bear in mind when you're looking at controls as we look down the track.
So where you're going to see heat stress? Places readily recognised as being hot, physically demanding work or jobs requiring protective clothing. So they're things to keep in the back of your mind.
By the way, as I go through, stop me at any time if you've got a question. We don't have to wait until the end. I'm more than happy to stop.
We'll look at four key factors now, just to give you an idea of the processes involved. Fluid replacement. I think the first thing to remember here is thirst is not always a good indicator of whether you're dehydrated or not. Usually by the time you start to get thirsty, you're about 2% to 3% dehydrated. So you want to try and keep on top of it. Rule of thumb; drink until thirst is satisfied, then have one more drink. I'm talking water here, by the way. So keep that water topped up. Frequent drinking rather than to drink a load in one sitting. Because you need to give the body time to get that fluid through the body.
Water is the essential component, but it must be an acceptable drink. I've been to sites where they said just drink the water. But the guys are saying well the water here tastes like camel sweat. I'm not going to drink that stuff. So you've got to make sure it's palatable, otherwise they won't drink it. That's an important aspect too.
Pre and post-hydration is important when there are restrictions on drinking. It's not often that you'll get these scenarios, but in the construction industry – asbestos stripping. They go into bubbles and encapsulations. They can't take water in with them. So then they may have to drink before they go in and have a drink when they come out to maintain that moisture.
How much salt? Always a contentious one, this one. Average Aussie diet is high in salt. More often than not, our doctors are telling us cut back on your salt. Right? So the other thing is, as part of our acclimatisation, the body produces this hormone called aldosterone. What that does is it reduces the salt content of our sweat. So someone that's acclimatised will sweat more than someone who isn't, but the sweat will be more dilute in salt. So they won't lose as much salt. So they're getting the benefit of the evaporation without losing all that salt.
I don't know how many times I've gone to sites and we get this question about electrolyte products. You know, you should be drinking staminade or Gatorade or whatever ade. They do have their place. But what we tend to recommend is you don't drink it all the time. Water's fine. But if you think you're going to be losing a lot of sweat and you need to replace that fluid, then what we tend to say is you have a glass of an electrolyte drink of whatever in the morning; you go out, you drink water while you're out there. When you come back for crib, you might have another one to put that back in. Often when you're having lunch, you're going to have a salty meal anyway, so you're going to be putting salts in. So if you're losing lots and lots of fluid, then yes, you will need to put in some of these other drinks. Otherwise, water is quite fine.
Acclimatisation – just very quickly on this one. Just be aware that if you go away from a warm climate for a period of time, say two weeks you go skiing somewhere; the body does lose its acclimatisation. So things like [long pause] the sweating rate will decrease. You'll get a more concentrated level of salt in the sweat. The effect of the heart – how the heart works reduces slightly in the volumes. So there is this loss of acclimatisation so you don't cope as well.
To give you an indication, I was called to one of our sites once and we had a guy collapse. I was talking to his supervisor and I said what happened? It didn't appear to be that he was doing more than usual. He said well, I don't know. He was out there doing his work and he just collapsed. Fair enough. What was he doing last week? Oh, he wasn't here last week. He was off – he was skiing in Queenstown. Oh, okay. He said yeah, he got back today and we thought because he'd had two weeks off, we'd give him the rougher job. So he got the worst job of the lot and he was totally acclimatised; so within an hour, he'd collapsed. So you need to be aware that that first day or so, you need to adjust to that acclimatisation process.
This one's a very topical one at times. Alcohol acts as a diuretic. It makes you pee more. So generally, a 200ml glass of beer or alcohol, in some people, will make you pass around about 300ml of fluid. So if you do your maths there, you're going to lose more than you're putting in. Okay? So you're going to dehydrate. The other thing too is electrolytes such as sodium and potassium are also lost in that process.
As a student, we did a lot of research in this area. Often, you'd get up in the morning and your tongue is furry and swollen. Mouth tastes like the bottom of a cocky cage. There's that little guy in your head, you know, boom-boom boom-boom boom-boom and he won't stop. A lot of that is due to dehydration. Not all of it. You still have to pay the penalty. There's some other things. But a lot of it is. So rule of thumb is if you're going to go out and have a few drinks, have a glass of water in between every now and then. Before you go to bed at night, throw down a glass of water or maybe even a staminade or whatever to help replace those salts that you've lost when you've been going backwards and forwards to the bathroom. When you get up in the morning or the middle of the night as sometimes happens; have another glass. In the morning, you'll find your body won't be as badly dehydrated and you'll feel a lot better.
We've done a lot of work in this area, seriously, in our minds. We've done specific gravity testing of urine of our guys as they come in of a morning. You'll be amazed at how many of those guys front up to work of a morning already massively dehydrated. Before they even start work. Right? So they're already at – they're losing straight away. We're now encouraging our guys to make sure they maintain their fluids and build them up. So it's an important one.
Very, very quickly on this. Acute health impacts. We're all familiar with these. You've got heat cramps where there is a lack of salts, whatever. Often, they'll happen at night. Not necessarily on the job. Heat rash; so there's prickly heat. Heat collapse, which is that fainting as we often see when the Queen comes out. That's as a result of standing still for a long period of time, pooling of the blood, lowering of blood pressure in the brain and the guy collapses. You'll find that probably in a couple of minutes, this guy will wake up because he's laying prone and the blood will go back to his brain and he'll wake up just in time to feel the pain. Heat exhaustion, we're starting to get into the serious ones. Heat stroke is the one you want to avoid. That one there is a medical emergency. If you get to the heat stroke stage, you've got to call the medic straight away. That's where we're starting to see some serious damage to the body.
I'm not sure – are these notes available or are the slides available, Peter? I'm not sure.
Okay, no worries. Well there's just some notes – there's some hidden slides where I talk about each one of those, which we won't touch on today.
This is one that's not as well known. Chronic heat illnesses. It's not as well understood. But what we're starting to see is an impact further down the track. There's a lot of studies now starting to go on in this area. Increased hospital admission rates for kidney complaints, ie. kidney stones in areas where we have got this chronic dehydration process. It impacts on the liver, the heart, digestive system, skin disorders, central nervous system and the reproductive process. Very, very important for ladies in the first trimester of pregnancy. A lot of damage can be done to the foetus in that period of time. So if you do have the scenario where you have got women of reproductive age that are trying to get pregnant, you need to be very, very conscious of that. There's some severe damage that can occur in that period of time. So there is long term impacts of heat.
Self-determination is a process we use [long pause] – it's basically saying you teach the guys what the symptoms are, you get them to understand what's happening and they need to basically determine themselves when it's time to have a break. There are all sorts of equations out there that you can use and heat stress indexes and indices that give you a guide; but the bottom line is they don't take into account how a person is feeling, what they've been doing the night before. They've been designed with fit, healthy military or university students, not the average 50 plus year old working out on site. Be aware that you need to be able to train the guys what to look for, let them understand their body and they'll know when they can have a break. Give them that – there's a bit of trust involved, but it does work. We've used in on a – well, we use that at all our sites now. Self pacing is very important.
So just a quick summary. Prevention of heat stress. Education; very, very important. The guys have to know – and the ladies – what the symptoms mean, how to identify them and what to do about them. Drinking of fluids, hydration is one of the key aspects of this. Cooling the environment – if you can't cool the environment, you cool the person. Acclimatisation; sometimes you have to reduce exposure time because you can't do anything about the environment. Where practice, reschedule jobs to a cooler part of the day. Have some of the office type work in the hotter part of the day. You know you hear about the people taking siestas? That's not a silly idea. A lot of that was developed because they were working in hot climates. So they would work hard in the morning and work hard at night and in the middle, they would rest, relax and take it easy. I don't know how that would go in the construction industry though. Excuse me mate, I'm just going to have a siesta. Encourage the buddy system. You need your guys to look after one another, to keep an eye on one another. They can see – often, the people don't really realise that they're suffering from the heat. Someone working alongside them will pick it up before they do.
Okay, some myth busting. Drinks containing caffeine are bad for you in the heat. Have you heard this one? True or false? [Long pause] true? It's false. All right? What you have to be aware of here is the study that was done probably about 40 years ago. It did show this. But more recent studies have shown that if you're an active worker or an athlete or whatever, caffeine actually – chronic intake of caffeine doesn't impact on you. There are still the odd individuals that it will have a diuretic effect with, but in the majority of cases, if you're an active person and out there, you won't get that diuretic effect. In actual fact – you think about it. You drink a cup of tea. It's got caffeine in it. How much caffeine compared to how much water? The majority of that is water. So it is adding to the fluid. The same goes with Coke. In my early days of presenting, you should never drink cola. It's bad for you. Well they're not brilliant, but again, most of it is fluid. There is some diuretic effect for some people but generally not. Okay? Not the best thing to drink, but they're not – they've had some pretty bad PR over the years. You can actually drink these things.
Red Bull? Different story. Yep. They're very high in caffeine and with them, you start having issues with the heart. The heart starts to get all funny and you get [long pause] – there are so many other symptoms and illnesses that come from it. Yeah, different story. Because it's so concentrated compared to the size, it's exacerbated the effect.
Changing from shorts to long trousers does not significantly increase your risk of heat stress. [Long pause] it's true. Because the way it works – is remember we talked about the evaporation process? The way that the body cools is it evaporates sweat from the skin. Well the ratio of skin and the amount of sweating [long pause] – sweat pores in the legs and that so far down doesn't have a big impact. It does have an impact. I'm not going to say it doesn't, because it does. But the ratio is so small that it doesn't really have a massive impact on heat stress itself. There's some studies done by James Cook University in Townsville that demonstrated this. So going from long trousers to shorts really doesn't have a significant [impact on] heat stress. What it does do though is increase your risk of skin cancers. You have to balance that off. I mean, ideally, if you worked in budgie shorts, you'd be right. You know, budgie togs? Lots of skin exposure, you'd evaporate a lot of sweat. You'd cool really quickly. But the risk associated with skin cancers, punctures, cuts, burns? It doesn't play off, you see.
There are no long term impacts of heat. We've just had this one. That's false.
Salt tablets are good for you in the heat. Who's had to take salt tablets? [Long pause] big no-no. Don't take salt tablets. Overloads the system. Avoid salt tablets. As I said, you've probably got too much salt in your normal diet anyway.
Cold milk is a good drink to prevent dehydration. [Long pause] it's false. You can drink it. It does have some benefit. But because of the high fat content in the milk, it takes a lot longer to get through the digestive system. So it doesn't have anywhere near an impact as what just plain water would. So hence, your lattes and your cappuccinos and whatever are not really doing a lot for your dehydration.
Drinking too much water can kill you. True. It's an illness called hyponatremia. A study done by some doctors at the Royal Brisbane Hospital on the Kokoda Trail guys showed that they were getting fatalities as a result of hyponatremia. The confusing part of it is they symptoms of hyponatremia are very similar to dehydration. So you think you're dehydrating, so you drink more water. But what happens is you lose the balance – what they call the isotonic balance or the salt balance in your cells and you get water going into the cells and they swell and cause all sorts of problems. There is a young lad in the US last year died of hyponatremia. Drank 16 litres – no? Yeah, 16 litres of water to try and avoid cramps.
That was over five hours.
Yep. We've tracked some of our guys and they – some of our smelter guys were actually losing ten litres of water in a shift. Because they're really hot and heavy work and they've been replacing it. But they're really extreme cases. The average person doesn't lose anywhere near that. So assessing some heat exposures…
You normally look at around about – you want it slightly cooled. When you say tap water/cold water? Room temperature water to cold water – I tend to say a temperature of around about 12 to 15 degrees is good because it helps cool down the body a little bit more. There's also been some studies looking at crushed ice and all those sorts of slurries and things. Adds just that little bit more benefit. But is it a big, significant change? No, not really. But it does help.
Yeah, good. Yep. Yeah, the chilled water is a little bit better for them, yes. Definitely.
Yeah, well it depends on what you drink. If you're drinking it about two or three degrees, then you're going to get that effect. But you'll find that if you don't put too much ice in it, you're around that 12 to 15, 12 to 16 where it's cool and it's absorbed readily. So the thermal shock from drinking iced water is that initial reaction. But eventually, it warms up quite nicely.
I'd like to go through this session just – this is quite an interesting one. This is a three step protocol. This relates to the keynote speaker this morning. If you can imagine us having the remote control. I'm going to show you three approaches. One is a simple approach where you only have to use the volume control. The other one is a technical approach where we have to use a lot more of the buttons. The third one is the physiological monitoring. I'll only touch on those last two. But we'll focus on that first one.
This is a process we developed many years ago. It's a very basic thermal risk assessment. Series of questions, you tick a box and they all add up and you get a number. Once you've got that number, it gives you an indication of the likelihood of a heat risk. Okay? This is the very first version. We've got copies of it if – you've got them there? Peter will hand around. They will give you an idea of how we can assess an environment. We took that and took it one step further and we built an Excel spreadsheet. Which we thought was really – oh, that's really getting up with the times. Well that's out of date now.
Next thing we did is we built a thermal app. Everyone's got apps these days. So now there's a thing called Thermal Risk app. It's available in iPhone, Android or Windows. Readily available. It's got all those questions except in a phone app. You don't have to be Einstein to run it. You can do it on the spot. You don't have to have lots of scientific instruments. All you need is access to know what the air temperature is and what the humidity is. Right? I'll show you how it works.
So that's what it looks like. You get a series of about 14 questions in this format and what you do is you push on – you know, are the workers exposed to the sun outdoors? If it's indoors or it's full shade; you just tap on one of those. That's just a front sheet. What it does is it gives you this final result and then it gives you controls. So if we go a bit further [long pause] – we're going back to there. So this is it, right? If you were to do it on the bit of paper we've just given you, this is what it would look like. [Long pause] I know what I've done. Okay, sorry. I'm jumping miles ahead of myself. I'll come back to that one. So that's the first. That's the basic thermal risk assessment.
If that comes out and says you've got an issue, then your next step is what we call stage two. This is where you call in your specialist; the hygienist. They'll measure all these things. They'll use a thing called a rational index, a heat stress index and they'll plug all those numbers into this little program. What it does is it estimates the body core temperature. So for this individual, for example, within – what's that? Sixty-seven minutes, he's reached the maximum core temperature of 38 degrees. So this is an example of someone that is under significant heat stress. Right? Because that's our limit there at 38. They've worked, so they've gone past it. They've had a break and then they've gone back out to work. So we'll do a little one of these in a minute.
Then if that's really serious, then we go to the physiological monitoring. This is heart rate and core body temperature monitoring. Okay? So this is the sort of thing that you really start to get into the specialist – that is the heart rate. You can see this individual; his heart rate was up above 170. His temperature was up around 38.4 on a couple of occasions. So that's the top end of the scale, which we won't look at. But these are the things that are available.
So let's look at the scenario. Installing structural framing on a low rise apartment site. Okay? So he's located on the first level platform three metres above the ground. There's no shade, no hot surfaces. It's going to take about an hour-and-a-half. Worker has a drink container with him. Workshop and crib room is about 200 metres away. There's a moderate breeze blowing. He's wearing standard cotton drill, so the high-vis gear that you're wearing. They've been trained in heat stress management. It's his first day back from two weeks of skiing holiday. Air temperature is 32 degrees, relative humidity 40%. So do we have a heat stress issue here? Is there a potential heat stress issue?
Now up until now, it's a case of oh yeah, could be, not sure. How do we assess it? Using that sheet I've given you, what you would do is you would look at 32 degrees air temperature, 40% relative humidity and we've got what we call an apparent temperature of 33 degrees. Right? So keep that in mind. [Long pause] then you would go through and, with all that information I provided, you would tick these boxes off. Hot surfaces? Neutral. Climbing up and down stairs or ladders? One level. And so on. It gives us – we add up our numbers. Use this equation here. It equals 42. Down here, it says if the total is 28 to 60, there is a potential of heat injuries or illness occurring if the conditions are not addressed. So it's given you a basic guide. There is a potential problem here. You need to do something.
If we use the app to do this, which does exactly the same thing except you're just pushing on buttons [long pause] – where it says tap for details; we tap on that. This is what happens. Those questions that we've asked down here are rated. Where you see this red three; that's an area where you've got an issue and you need to do something about it. Right? So acclimatisation, distance from the cool rest area and sun exposure.
So what am I going to do? I'm not sure. So if you go back and you tap on this tap for controls, it comes up with this. So we find the category where we've got the issues and we look at some of the controls that they're recommending. So sun exposure. Well, could we conduct the work at night? Can the work be done indoors? Can we put up shade barriers? Can we do it early morning or late afternoon? Have they got hats, sunscreen, light coloured clothing, ventilated clothing? Whichever ones you go, you can sort of look through this and it gives you a guide. It's not the ultimate, but it is a good, basic indicator. It's simple to use. Everyone's got mobile phones these days, so in probably about five minutes, you can do a quick risk assessment and go out there and put some controls in place at the start of the day.
Scenario two. Workers preparing formwork for a building slab. Full sun, no shade, two hours between crib breaks taken under a tree 20 metres away. Drink bottle over by the tree. Wearing light shirt and shorts. No heat stress awareness training. No breeze. Have been doing similar job in the area for two weeks. Temperature 34°C at 45%. Gut feel; is this going to be a problem?
Right. So sometimes you don't even have to go that step. But it gives you a guide. So if we do the same thing again. Our key areas here are sun exposure, the exposure period – so it's two hours. They haven't been trained and we've got no air movement. So they're the areas we need to work on to improve to help reduce that – and they're our controls.
This is the one I wanted to get to. This one's got a bit more to it. Electrician working in a ceiling cavity in central Queensland. Right? [Long pause] these are the parameters. So we've done our basic – you wouldn't even probably think about the basic thermal risk assessment if you saw this. I mean, there is an issue here, isn't there? Dry bulb – so that's air temperature; 40.9, 41 degrees. Globe temperature is radiant heat. So that would be heat that was probably on a tin roof and the person's underneath that. Relative humidity's not that bad. It's actually quite good. Air velocity? You're in a roof cavity. There's no air movement. They're doing a reasonable amount of work. He's crouching all the time, single layer clothing and he's acclimatised.
So if we plug that into our – now this is where we start to get a little bit more technical. But bear with me, because it will become obvious why I'm doing this. So we call in our experts. They use this program. You can see they plug in all these numbers. The job's two hours. Air temperature's 41 and so on. You know, 175 in metabolic rate. He's acclimatised. He can drink whenever he wants because he's got a bottle up there with him. But he's crouching and his clothing index is about 0.8. We plug that in. Sure enough, within just over an hour, his core temperature has hit 38 degrees. So he's at risk. Now this job was going to go for two hours. Within two hours, it's up to 38.4 and it's going to continue to rise pretty rapidly. So we've got to do something here.
What are our options? [Long pause] give him a rest? Okay. We give him a 30 minute break at the end of the – you can work for two hours, then he's sitting up in the roof and he can have a break. That's what happens. So what happens to his core temperature? It comes down to 38.2. It really doesn't do much, does it? How about we get him to come down and let him have a break in his air-conditioned cab of his car or something? [Long pause] that's a bit better. But look what's happened. It gets down to 37.6. But he's spent all this period of time above the core temperature. So what happens when we put him back to work? [Long pause] so we put him back to work and within about 34 minutes, roughly, he's already hit his limit again. So we're putting him back at risk. So is that an acceptable approach? It's not, is it? So what are we going to do? What would suggest?
Yeah, we'll come to that in a minute. What about if we gave him a break somewhere down here? Okay? So about – where does he hit 38? He hits 38 about there. Righto, so we'll give him a break. Give him a break after 60 minutes. That works. He gets up to 37.9, he has his break in the air-conditioned room, he goes back to work and he's quite safe. We've kept him underneath that limit. Is that acceptable? Right?
So that's the work rest regime. That's the concept of breaking it up. Productivity wise, it's not brilliant though. Right? You've got to keep that in mind. So the suggestion was increase the air velocity. So we're going to increase the air flow. [Long pause] what happens? [Long pause] it flattens off nicely. So what that's telling me is that the evaporation of sweat is cooling the body enough to keep the core temperature below 38 degrees. So that was the correct solution. He can work quite comfortably for two hours in that environment without having too much stress on him. So it's little things like that that we can do. It's not always a highly technical approach what we need. How do we increase the air flow? Fans and things like that.
So some takeaways for you. Managing heat stress is not just about the air temperature. There are many other factors that can impact on the heat strain of a worker. We saw that right at the start. There's the environment, the work they do and the individual themselves; how they're coping. Educate employees and supervisors so that they understand heat stress and the controls available. You saw a simple thing like putting a fan in made a massive improvement. Mind you, there are scenarios where if you put a fan in, you could actually make it worse. But that's normally greater than 42, 43 degrees. Then we get what we call the fan forced oven effect. We start to cook our people. So beware of that one.
Heat stress consequences begin well before we get to the classical illnesses. Act early and prevention is much simpler. Get in there early. They need to be able to pick out when it's starting to affect them. I was a TA for a fitter once working at a power station. I asked him how does he know when to have a break. He looked at me and he said oh, I have a break whenever my eyebrows start sweating. I thought oh yeah, this guy's having me on. We put some monitoring gear on him – we did actually physiological monitoring. I was, as I said, working as a TA and we were working on the boilers. It was 60 odd degrees C. He said that's it. Time for break. We did this all day. Next day, we downloaded his core temperature and heart rate graph. He had it down to a fine art. As he would approach 37.9, it would drop where he'd have a break. It would come back up again and – his way of identifying when he'd had enough was his eyebrows sweating. Now I don't know how scientific it was, but it worked and I wasn't going to knock it. So they understand their body, they understand the symptoms. That's what that's all about.
When planning jobs, take into account the heat and plan in the controls. If you're going to work next week and you know it's going to be 40 odd degrees; what are you going to do about it? You may have to restructure how you do your job. Start earlier, have a break in between, work a little bit later. Make sure all the fluids, sunshades, all those sorts of things are available before the job starts. Don't just go out there and then find out oh geez, I've got a problem here.
Lastly, directly or indirectly, heat stress can maim and kill. We've seen it happen. Right? I was involved in a court case recently where a young lad – it was a fatality as a result of heat stress. It does kill. And if it doesn't kill, it can cause very severe brain damage. So keep it in mind.
If you need some references, if you're a geek like me and you like to know everything there is about it, that's the bible for managing heat. It's called "Human Thermal Environments". This one's a much simpler version. It's called "A guide to managing heat stress: developed for use in the Australian environment". It costs you about $30 and it's from the Australian Institute of Occupational Hygienists. Very basic terminology. It's not too technical and there's some good practical ideas. Also if you're interested, there is a blog at http://www.thethermalenvironment.com. A lot of useful stuff in there. There's policies, toolbox sessions, all sorts of things that you can take off there. There's also a Twitter.
So thanks for your participation.
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