Safety Series: Hydrocarbon Extraction

by | May 1, 2019

Today we would like to take a moment to discuss a less exciting, albeit crucial piece to the cannabis processing puzzle – Safety. This will be a multi-part series, and today the primary focus will be concerning closed loop extraction; utilizing light hydrocarbons as our primary extraction solvents. We will also briefly touch on CO2 extraction, as well as ethyl alcohol and other commonly used chemicals in the cannabis manufacturing environment, in later installments.

The most prevalent accepted safety concern for light hydrocarbon extraction is the risk of explosion. The same properties that make our solvents of choice so favorable in these systems, are also the exact reason they can be so dangerous in the first place. This metaphorical double-edged sword can seem complicated at first, but further analysis proves this concept quite simple.

Butane has a boiling point of roughly zero degrees Celsius. Therefore, in standard atmospheric pressure scenarios at or below this temperature, butane will remain in the liquid phase. When temperatures above zero degrees Celsius are present, given all other parameters remain identical, butane will reside in a gaseous state. This is great for closed loop extraction because it allows us to easily manipulate the phase of our extraction solvent at different stages of the process utilizing relatively low thermodynamic energy. In short, it’s easy to maintain butane as a liquid to strip the biomass of the desired active compounds, and then turn it into a gas to not only remove it from our freshly extracted product, but also recycle it for further use.

This chart demonstrates the thermal-physical properties of butane.
c1d1, Safety Series: Hydrocarbon Extraction

At this point you may be asking yourself, “What does this have to do with safety?” If everything is running smoothly, and your extraction system is operating as it was designed, the answer is nothing. However, what happens when a gasket fails, or a fatigued operator forgets to perform a routine maintenance check on a high pressure tri-clamp connection? A leak is sprung. Pressurized liquid butane is escaping the system rapidly, turning into a gas instantaneously.

When butane is in the gaseous phase, it occupies 233 times as much volume as it does in liquid phase. This is referred to as expansion ratio. In basic terms, this means that one gallon of liquid butane in a solvent storage vessel would become approximately 233 gallons of gaseous butane if the entire gallon was vented into the atmosphere. The lower explosive level of butane (commonly referred to as LEL) is a staggeringly low 1.86%. You read that correctly. A concentration level of less than 2% can create a potentially explosive situation in your extraction lab.

Three basic elements must be present to create an explosive event in any scenario.

1. A flammable substance in high enough concentration (LEL)
2. An oxidizer (oxygen)
3. An ignition source (flame, static, etc.)

Now let’s take a look at how we are able to limit these factors.

First and foremost, all compliant cannabis extraction must take place in a properly classified environment. Arguments can be made that the nature of extraction falls under C1D2 guidelines, but for safety’s sake and industry standard practices C1D1 is the universally accepted classification.

C1D1 is the acronym used to refer to a Class 1 Division 1 environment. As defined by NFPA 70 (National fire code) a Class 1 Division 1 environment is required in any location where:

1. An ignitable concentration of flammable gas or vapor can exist under normal operating conditions.

2. An ignitable concentration of flammable gas or vapor can exist frequently because of repair or maintenance operations or because of leakage.

3. Breakdown or faulty operation of equipment or processes might release an ignitable concentration of flammable gas or vapor and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.”

An environment must adhere to strict national fire code guidelines to be classified as C1D1 compliant. The first order of business is an exhaust system to dilute the concentration of flammable gases to a non-explosive level should they become uncontainable. A minimum air exchange rate of 1 cfm/ft^2, (though double that is preferred) is the go to specification in this scenario. We prefer to interlock the exhaust system with flammable gas detection equipment in our designs. This allows us to run a safe, static exhaust rate during baseline readings as well as the ability to instantly increase ventilation if flammable concentration levels are reached. This will limit the first factor in an explosive situation.

Next is compliant equipment. All electrical connections and components housed or used within the C1D1 environment must be classified for use in said environment. This includes lights, security cameras, gas detection equipment, electrical plugs, gas compressors, etc. These items are often overlooked and are crucial to ensuring safe operation of your extraction lab. By utilizing such equipment we are now controlling the third factor in an explosive situation, ignition.

There are several other factors to consider when designing a compliant extraction environment. For the sake of this series we have only scratched the surface. Feel free to contact us directly to discuss state specific or in depth issues.

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