“The faintly lit hatchway lay in the dark…like a grave yawning at judgement day in some old apocalyptic painting.” — Cormac McCarthy
One of the appeals of craft distilleries and microbreweries is that they produce small batches, so a lot of care goes into each batch.
Small batches, by their very nature, require small additions of ingredients. While some additions are large enough (and liquid enough) that they can be pumped in through a pipe, small additions are typically through an open hatch. Hatch activity can include sampling, liquid ingredient additions when the quantities are small enough, solid ingredient additions, either granulated or as powders, in any quantity.
Distillers and brewers need to be aware, however, that there are hazards associated with hatch activity. The nature of those hazards depends on what’s already in the vessel and on the material being added through the hatch.
Hazards that Depend on the Contents of the Vessel
Whenever a volume of something—anything—goes into a vessel that is open to the atmosphere, an equal volume must come out of the vessel. Most likely, the volume displaced from the vessel will be from the headspace in the vessel. Even more likely, the displaced volume will come out through the open hatch. Right where the distiller or brewer is standing, making the addition.
What will be in that displaced headspace volume? If the vessel contains a liquid, it will be the vapor of the liquid, at whatever concentration its vapor-liquid equilibrium dictates. A toxic liquid will result in toxic vapors in the headspace. A flammable liquid will result in flammable vapors in the headspace. Ethanol is both toxic and flammable.
Toxicity – OSHA’s permissible exposure limit (PEL) for ethanol is 1000 ppm, or 0.1% by volume in air. At a normal room temperature—68°F (20 C)—the ethanol concentration in the vapor exceeds 1000 ppm whenever the liquid mixture exceeds 5.32% alcohol by volume (ABV). The vapor in the headspace above ordinary beers has a high enough concentration to exceed OSHA’s PEL for ethanol!
As the temperature of the liquid goes up, so does the partial pressure of ethanol in the headspace, and hence the concentration. Stated another way, the hotter the liquid mixture, the lower its proof needs to be to exceed OSHA’s PEL for ethanol in the headspace. At just 77°F (25 C), a 4.08% ABV beer will generate an ethanol concentration in the headspace of 1000 ppm.
Flammability – Flammable liquids are a different story. When a flammable liquid is in a vessel at a temperature below its flash point, it won’t generate a vapor pressure high enough to go above its lower flammable limit (LFL) and form a flammable mixture with air. The LFL of ethanol is 3.3%. At a room temperature of 68°F (20 C), a mixture of ethanol and water must be 80% ABV (160 proof) or higher to form a flammable mixture with air. That means that at room temperature, beer isn’t flammable and neither are finished spirits that have been proofed down to 40% ABV (80 proof). But the new make, aka “white dog”, “white lightning”, or “moonshine”, coming directly from the still certainly can be.
Again, the ethanol concentration in the headspace goes up as the liquid warms. Perhaps more meaningfully, as the liquid warms, it takes a lower proof liquid to create a flammable mixture in the headspace. At 79°F (26 C), an 40% ABV (80 proof) liquid will support a flammable mixture in the headspace, and at 100°F (37.8 C), a 35.5 proof (17.8% ABV) liquid will support a flammable mixture in the headspace.
An operator making additions through a hatch from which a flammable mixture is exiting is vulnerable to being engulfed in a flash fire, especially if their clothing and movement generates the static spark needed to ignite it.
Hazards of Liquids Addition
It’s not just the movement of people at the hatch that generates static electricity, however. Liquids can carry a static charge. When allowed to freefall through the headspace, it is possible for the static charge to jump from the falling liquid to the wall of the vessel. This spark then becomes an ignition source for a flammable mixture in the headspace of the vessel.
To reduce the likelihood of a static discharge in the vessel headspace, large volume additions are typically subsurface, through a dip pipe. Using a dip pipe for small liquid additions is generally not practical, however. So, small liquid additions through an open hatch means that there is a static discharge problem. To address static during these and other hatch additions, it is important that both the person at the hatch and the container of liquid that they are pouring from be grounded and bonded to the vessel, bringing them to same electrical potential.
Hazards of Solids Additions
Solid materials, whether powder, granules, or pellets, contain fines. These small particles easily disperse as a dust cloud. Respirable dust poses a health burden on anyone exposed. Silica dust can lead to silicosis, but any respirable dust is a hazard. When an operator adds a solid through a hatch, the displaced headspace vapor will sweep the fines out with it, exposing whoever is standing there to respirable dust.
When the dust is a combustible dust, the dust cloud becomes a greater hazard. Not only is there the exposure to respirable dust, but there is the potential for a dust cloud fire (a flash fire) or when confined, a dust cloud explosion. Whoever is at the hatch when the cloud ignites is going to be standing in the midst of it.
Ergonomics
No discussion of manual hatch additions would be complete without a discussion of ergonomics.
Many distillers and brewers use grain that has been milled elsewhere, in order to avoid the trouble and grain dust hazards associated with milling it themselves. They often receive this milled grain in 50-pound bags. Opening and dumping grain bags is a task ripe for ergonomic injury. There is equipment available to improve the ergonomics of this operation, but there are obstacles to its adoption, not least of which is cost.
Another common implement for hatch additions is a five-gallon pail. A five-gallon pail will typically contain around 40 pounds, which is a heavy lift of something that is also awkward to manage. This can lead to strains and musculoskeletal injuries. Because the container is awkward, pouring it into a hatch can also lead to spills, which have their own environmental and personnel exposure issues. It is important to ensure that every hatch addition is a manageable amount, and that buckets are not full to the top, but left with adequate freeboard.
Bigger Than a Cook Pot
Although hatch additions resemble adding ingredients to a stove-top cook pot, they’re bigger and have bigger hazards. However, there are also measures available to address each hazard associated with hatch additions. These include proper PPE, such as respirators and flame-retardant clothing, and may also include bonding and grounding, vapor exhaust, dust collection systems, and appropriately sized transfer containers.
