THCa Decarb Pressure in Sealed Jars
The vessel model combines heated trapped air with CO2 produced by decarboxylation. It cannot establish whether a jar is safe.
I built the pressure model because heating a sealed glass jar bothered me. I wanted to know how much pressure could come from the air already trapped inside and how much additional gas THCa might produce.
The calculator uses ideal-gas relationships so those contributions can be examined separately. A number from this model is not a pressure rating for a glass jar.
Air heating and CO2 are separate contributions
Trapped air increases its absolute pressure as its temperature rises at constant volume. The ideal-gas relationship gives P_hot = P_sealed × T_hot / T_sealed, with temperatures in kelvin.
Each mole of THCa converted produces one mole of CO2. The CO2 contribution is nRT/V, where n comes from converted THCa mass / 358.47 g/mol and V is the free gas headspace. The model adds the two partial pressures and subtracts ambient reference pressure to display gauge pressure.
The free-gas volume is not the jar capacity
A nominally 500 mL jar containing 400 mL of material does not have 500 mL of headspace. The effective free-gas volume, not the printed container size, is the quantity the ideal-gas equation needs. Changes in fill level or material expansion change that volume.
Because the CO2 term is inversely proportional to volume, uncertainty in the headspace can move the result substantially. Sealing temperature, ambient pressure and incomplete reaction add more uncertainty.
What the pressure estimate leaves out
The model assumes a rigid vessel with constant headspace and a dry, ideal gas mixture. It omits solvent and terpene vapor, gas dissolution, leaks, pressure-dependent vessel deformation, phase changes and gas/sample temperature differences.
Those omissions do not consistently bias pressure upward or downward. The estimate is neither a conservative safety bound nor evidence that a sealed glass container can withstand heating. Vessel design, defects, thermal stress and pressure limits are outside the calculation.
References
Questions about this calculation
Can this calculator tell me whether my glass jar will break?
No. It predicts idealized gas pressure under entered assumptions. Glass strength, flaws, thermal shock, vapor phases and vessel ratings are not modeled.
Does the pressure estimate include terpene or solvent vapor?
No. The modeled contributions are heated trapped air and CO2 released from converted THCa in a fixed headspace.