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What is adequate ventilation? 

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We are doing a build out of a distillery that will occupy approximately 600 sq feet within a 13,000 sq foot building that is F-1 occupancy.  The consulting engineers believe we need to classify the area which then kicks in special placement and sealing of electrical services.  I have found several tidbits on the web that tell me this is not true as long as adequate ventilation is present.

 From reading various items it seems that adequate ventilation means 6 air changes per hour, or 1 CFM per square foot of floor area used for storage.  The requirement is to keep the vapor concentration from exceeding 25% of the Lower Flammable Limit.

This is new building and the air exchange would be around 3200 cfm.

 We have sprinklers throughout and will not exceed 240 gallons of storage, which is our MAQ.

 The total square footage of storage space will be approximately 30 square feet.

 All storage will be done in 55 gallon stainless steel barrels.

 There are no walls within the 13,000 square feet.

 We will have two 125 gallon electric stills.

 From both a code stand point as well as a “real life” safety stand point I do not think we need to be classified. 

 One of the points the consulting engineers bring up is:  How can we determine there will be no pooling of the vapors that would exceed 25% of the LFL?  My first thought is to run a floor fan 24/7/365 to disperse any potential pooling but if there is another common sense approach I’d like to hear it.

Any ideas of how not to be classified are appreciated

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Your problem will likely not be the general exhaust rate, but a plan for spills or swamping of the condenser for the stills: either can produce a large release of ethanol. We dealt with that by having an air exchanger running continuously for the small background air exchange, and a large exhaust fan for full exhaust in the case of a larger release of vapor. Ours is manual, but some places may require that to be automated and tied to an ethanol sensor (very expensive proposition). Pooling of vapor can probably be treated similar to CO2, since the densities are close. But to get that much ethanol means you have had a major release, not a small background build up.

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One of the points the consulting engineers bring up is:  How can we determine there will be no pooling of the vapors that would exceed 25% of the LFL?

Ask your engineers to calculate the amount of ethanol required to be vaporized to be able create pooling of vapor at 25% LFL with no ventilation in a 13,000 square foot space. 

-----------------

Someone check my math...

Let's just say, for giggles, we are talking about 2 feet of pooled vapor in the 13,000 square foot space, 26,000 total cubic feet at 3.3% (the LFL of ethanol).

Let's say 736 cubic meters to keep things simple.  At 3.3% ethanol, we're talking about 24.3 cubic meters of ethanol vapor in that bottom 2 foot space (736 total)

Stay with me here, that's 24,300 liters of ethanol vapor.

I might be wrong but a mole of ethanol is 22.3 liters volume.

24,300 liters / 22.3 moles = 1089.69 moles of ethanol

Ethanol is 46.07 grams per mole.

That's about 50.2kg of ethanol, or about 64 liters, a little under 17 gallons of pure ethanol vaporized to fill a 2 foot tall, 13,000 square foot space (no walls) to hit the lower flammable limit.

Now, you'll have a 125 gallon still.  Playing with numbers, you would need to vaporize all of the alcohol in a 125 gallons of a 13.6% wash to hit the lower flammable limit.  

This would probably take something like 4 hours of blowing vapor out of the still, with no air exchanges.  I suspect this would be noticed.  Or at least I hope it would.

So, to hit 25% LEL, in that 2 foot tall space, we'd be talking about blowing vapor for a full hour.

However, fill both stills with 30% alcohol, and blow vapor, and you'll clearly see that it is possible to hit the 25%LEL in something closer to 15 minutes.  Garbage truck backs into your SUV in the parking lot, you run outside flustered and lose track of time, because you are having a shitty day, you have a water issue and the condensers lose water flow.  You'd still need to blow vapor for about an hour to hit the actual LFL.

Point being, under normal operation it's highly unlikely to liberate enough vapor to ever hit the LEL of ethanol, it's only under a catastrophic situation that this would happen (read up on your area classifications, as this is a really important point).

Also, looking at it from a storage perspective.  Assuming only 1 air exchange per day, you would need to lose approximately a full 10 gallon barrel of whiskey at 120 proof to hit the LEL in the same scenario.  Think about this, you would have to evaporate nearly a full 10 gallon barrel of whiskey, every single day, to get to the LFL, that's losing more than 3500 gallons of whiskey a year.  Again, highly unlikely.

All that said, when you spill ethanol, realize that none of the math above is relevant anymore.

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our engineer required 6 air changes a hour , with explosion free fans ,drawing air from floor right behind the stills .  incoming replacement air has to drawn from out side air pulled thru a heat exchange . the whole thing is very expensive horse crap imo , but i guess if they dont go over board with the rules some dip shit will be heating his still with a propane torch and blow himself up lol . its easy to over engineer things when there not paying for it . 

tim  

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Thanks guys,

The input is terrific.  A special shout out to Silk for talking engineer, to Bluestar for making me think about spill control and to Tim for letting me know that others have had the same issues we are currently trying to tackle.

For the next guy that has to go down this path I offer some additional information.  Consult the International Mechanical code.  Although section 502.8.1.1 tells us how much air exchange is necessary in an area of hazardous vapors, both 502.9.5.2 as well as 502.9.5.4 say that 502.8.1.1 is only applicable if the MAQ is EXCEEDED. 

 

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Sharing this not because I think you should go argue against your engineers, I'm sharing because most engineers don't have a grasp about the volumes of ethanol that are typically worked with.

Knowing nothing about distillation, you would assume the worst.  When you realize someone needs to completely boil off a complete batch of wash to even come close to hitting the limit, it puts things into perspective.  Once you factor in passive air exchange, the numbers become even higher.

We had an architect question us about ethanol vapor in storage, until we ran the same math and it became pretty clear that we'd need to store tens of thousands of gallons in barrels in a tiny space for evaporation to pose any risk at all.

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Any chef will happily flambe your cherries jubilee with a 40% spirit.

Ethanol’s vapor phase is heavier than air and will accumulate at the lowest level.

Ethanol vapor and air will mix and form an ignitable flammable concentration from 3.3% to 13.3%.

 

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4 hours ago, Silk City Distillers said:

Sharing this not because I think you should go argue against your engineers, I'm sharing because most engineers don't have a grasp about the volumes of ethanol that are typically worked with.

Thanks Silk

The disagreement started before the post but I am not being difficult about it.   Frankly if the costs are not a lot more going their way I am going to drop the issue.  You are correct, they do not have a grasp.  The first problem came when they said that two still equaled 250 gallons thereby exceeding our MAQ.

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5 hours ago, Hudson bay distillers said:

 is alcohol proofed down to below 50 % abv considered explosive 

Alcohol is not explosive. Gasoline is not explosive. A tree is not explosive.

All are combustable, but not explosive.

Take that alcohol. gasoline, or tree and turn it into a vapor (in the trees case turn it into dust) with a nice mixture of oxygen and it becomes explosive. As far as my grade school science goes you cant have 20% alcohol vapor or 50% alcohol vapor because it is no longer mixed with water at that time its 100% alcohol vapor in molecular form that is now diluted in the air.

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The chances of creating an ethanol explosion from fumes is remote. Once the fuel air mix exceeds 13% the explosion danger is passed. Its the same with Natural gas. Past 17%, its pretty safe. Coming from a NG background, I often had to explain that gas wasen't nearly as dangerous as advertised. That being said, its always prudent to ensure the explosive conditions are not present.

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Sort of...  When we were faced with making a choice, our electrician kept offering us very expensive options - in excess of $6k. After much debate, what we did was get powerful regular fan(s), we have three, and we mounted them on the exterior of the building, thus circumventing the XP requirement. However, since then, I have discovered that the electrician was trying to take advantage of us. Actually, XP fans are easy to come by and not near as expensive as suggested...  https://www.industrialfansdirect.com/collections/explosion-proof-fans-and-blowers

...is a good place to start generally. If you are looking for local or CDN sources, try the farmer's supply, as most of the XP fans sell to meet their farm/grain needs.

 

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The XP appliance is only a small part of the cost, remember that you need threaded conduit, explosion proof glands, elbows, and couplings.  Very expensive fittings, and incredibly labor intensive compared to running normal conduit.  The materials and labor to pull a circuit to an explosion proof piece of equipment (Like a $1000 fan) could possibly cost as much as the equipment.

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14 minutes ago, Silk City Distillers said:

The XP appliance is only a small part of the cost, remember that you need threaded conduit, explosion proof glands, elbows, and couplings.  Very expensive fittings, and incredibly labor intensive compared to running normal conduit.  The materials and labor to pull a circuit to an explosion proof piece of equipment (Like a $1000 fan) could possibly cost as much as the equipment.

Only if yer local regulator says you need to.

We ain't making gunpowder here. No need to spend a million dollars that you don't have on safety equipment that you will never use.  If you have enough alcohol vapor in your conduit to create an explosion you have a lot bigger problems on yer hands.

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29 minutes ago, MGL said:

If you have enough alcohol vapor in your conduit to create an explosion you have a lot bigger problems on yer hands.

Not to mention lost profits!

 

 

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6 hours ago, Silk City Distillers said:

Past 17%, its pretty safe.

Suspect your eyes and nose would burn like hell and you'd be recognizably drunk in a pretty short time period.

You have to ventilate for 2 reasons: fire safety and OSHA exposure limits. The OSHA exposure limits are MUCH lower, 0.1% (1000 PPM), so THAT is what drives the need to have continuous ventilation, and enough convection to prevent pooling. If you have any significant release or spill, you will get above that limit, and you will have to increase exhaust to come back down to the limit. But then you might have enough local concentration and/or pooling to reach the explosion limit, and that you have to do major exhaust for.

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7 hours ago, Glenlyon said:

Sort of...  When we were faced with making a choice, our electrician kept offering us very expensive options - in excess of $6k. After much debate, what we did was get powerful regular fan(s), we have three, and we mounted them on the exterior of the building, thus circumventing the XP requirement. However, since then, I have discovered that the electrician was trying to take advantage of us. Actually, XP fans are easy to come by and not near as expensive as suggested...  https://www.industrialfansdirect.com/collections/explosion-proof-fans-and-blowers

...is a good place to start generally. If you are looking for local or CDN sources, try the farmer's supply, as most of the XP fans sell to meet their farm/grain needs.

 

Correct, the most common explosive ventilation is for dust from grain.

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