I work at a Petroleum Refinery and every year we review the “Plant Safety Manual”. One item is the required response to the “Toxic Release Alarm”. This covers the situation where you are out in the Plant and the alarm sounds, indicating that somewhere there is a gas release of something that can kill you.
The contentious issue is the recommended action: determine the wind direction and then move cross-wind to the nearest Emergency Assembly Area (EAA).
Note that there are wind-socks readily available to help you visually determine the wind direction. Also, note that EAA’s are not necessarily protected (many are outdoors), but they all have communicators that can give you furthers advisements on the emergency.
I’m not sure what the logic is regarding the “move cross-wind”. If you take the hypothetical situation where you are in the center of the Refinery and the wind is from the North, what would you do if the alarm sounded?
You need to move as quickly as possible from the ‘Protective Action Zone’*. Moving cross wind is the most likely shortest route away from the plume - if you are already in the plume.
If you are out of the plume you can move into the plume by moving crosswind.
Evacuation direction should be cross wind if you are already in the plume.
I assume that the alternative you’re considering is to run downwind? Unless the wind is very slow, you’re not likely to outrun it. And the plume already probably extends past your starting position, so you’d have to run * faster * than the wind in order to get clear. What’s more, you’d have to keep running because the plume would keep following you. Crosswind is the shortest way out.
Excuse me for laughing at what could be a potentially lethal situation but the image strikes me funny.
A cloud of who knows what is suddenly released and instead of running for your life, your employer wants you to march over to something called the EAA so some guy with a clip board can see if you survived.
I used to work for an E&C firm, predominantly in oil refineries. We would get the same safety lectures, including what all the various horn signals meant (which we usually forgot quite promptly). On one refinery, the instructor made it very easy for us. After all the standard instruction, he just said that, if we heard an alarm, to follow the operators, unless they were wearing firefighting gear. In that case, run the opposite way.
That was way easier to determine that which way was cross-wind.
EAAs save lives. The idea is to run for your life, but to end up somewhere where the guy with a clipboard can see you’re alive.
If you don’t do it that way, the emergency response folks - firefighters, for instance - might get themselves killed looking for you because they think you’re still inside.
I spent some time working on biodiversity surveys at Shell oilfields in Gabon. All vehicles were required to park with the front of the vehicle facing out. As I understood it this was so no time would be wasted backing out in case you had to flee during an emergency.
However, to prevent road accidents due to speeding, all the vehicles had a regulator preventing you from going more than 40 kph (25 mph). If you tried to exceed that, the motor would cut out.
This always made me visualize a scenario of all the vehicles peeling out from their parking spaces, and then being forced to tootle along at 25 mph while being pursued by a giant fireball.
That sounds pretty reasonable to me, but can you provide a cite. I have no idea how many toxic events occur, or what the death rate per event was before and after this system.
I design industrial controls for a living, and as such I go to a variety of different types of plants. It always struck me as slightly funny that one chemical plant’s safety training basically boiled down to “look for someone with a company hard hat and run wherever he goes.”
In that and many other plants, you don’t just want to run for your life because you can easily run and hide next to something that isn’t safe in an emergency. For example you don’t want to hide next to the BIG TANK OF EXPLOSIVE STUFF when some cloud of stuff that makes it explode is drifting around the area, nor do you want to run and jump into a nearby ditch when the cloud of flesh eating goo is heavier than air and will settle into the ditch and kill you. Specific areas are set up where you won’t get exploded or suffocated or dissolved or some such, and when the you-know-what hits the fan you want to end up in one of these areas so that someone with a clipboard can tell you where to go and what to do next.
The move cross wind instruction in the OP is pretty obvious. The big cloud of flesh eating goo is going to get spread out in the direction of the wind. If you do downwind you’ll be going in the same direction as the cloud of goo, and if you go upwind you’ll just be following the cloud of goo to its source. The quickest way out of the cloud of goo is off to either side. If the wind is from the north, haul ass either east or west to wherever the closest safe place is.
Dont know about “Protective Action Distance”. The distance from the PAZ to safety will vary depending where you are in the zone. This distance will always be less than half the downwind distance (because the zone is square…draw a diagram).
There is the “Isolation Distance”, which is the radius of a circle around the release point. This defines the “Initial Isolation Zone”. The IIZ takes into account risk of wind reversal, diffusion and turbulence.
I should stress that I don’t know how many toxic events occur either, but this system is for all emergencies, not just toxic releases. Fires, for instance.
I think that everyone agrees that moving crosswind is correct if you are already in the plume.
But… if you are not then moving crosswind has a high degree of probability of getting you into the plume. In actuality, the EAA’s that are outside are all at the edges of the refinery. To get to them you have to transverse half the width, and that means that I have a 25% chance of being killed. Not good odds. It seems the move I move across, the more likely I am to find the plume, so why am I moving at all?
How about this: if the wind is light, move downwind. If it is brisk, move upwind.
My thinking is that, in both of these scenarios, you are in trouble only if the plume is directly upwind of you. If the wind is light I can outrun it, or at least delay the onslaught until the cloud has dispersed a bit. If the wind is brisk, if I’m still alive when I hear the alarm, then I’m guessing that the cloud is not upwind and that’s where I’m going to go!
Like I said earlier, you need to know where the source of the release is, so that you can define the protective action zone. Once you know this you move away from the plume, crosswind.
If you move upwind, you are moving into an area with a greater lilkelihood of encountering higher concentrations of the plume.
If you move downwind, you may remain in the plume. I wouldnt count on guessing the wind speed and running faster than it.
Your refinery management should have the release point identified at the outset of the incident. Once this is known an ‘atmospheric dispersion tool’ should be used to model the plume. These tools imediately predict the tragectory and fate of the plume based on wind speed, vapour pressure and environmental degradation of the released substance. This information should be communicated to personel involved in the evacuation, so that different work areas (wardens) know how to respond - e.g. which EAA to muster to.
The point is, you want to be exposed to the lowest concentration of the substance for the shortest period of time.
I worked at various chemical sites for a major chemical corp, not petroleum but equally hazardous - mostly inorganic compounds with inhallation hazards and issues when mixed with moisture in the air (or lungs). The rule was to move upwind…never mentioned crosswind.
We were also given escape respirators, but some Army guys tell me they’re worthless. Luckily, I never had to find out… - Jinx
Sure, but do you want Joe Sixpack, the guy that it took six months to learn how to wash down the asphalt, to have to figure this out when the siren sounds? I think that the idea is to keep things simple, so they can be easily remembered in an emergency.
