Often confused · Refrigerant safety
The 80% fill rule and the weight math behind it
The 80% fill rule caps a recovery cylinder at 80% of its capacity in liquid refrigerant, and on the job you hold that limit on a scale, working from the water capacity (WC) and tare weight (TW) stamped on the cylinder.
Part of Refrigerant safety in the Study guide
The numbers in the calculation
- WC — water capacity
- The weight of water that fills the cylinder completely, stamped on the cylinder. It measures volume, expressed in pounds of water.
- TW — tare weight
- The weight of the empty cylinder, also stamped. It's added back at the end because the scale weighs the steel too.
- Specific gravity
- How dense the liquid refrigerant is compared with water. Above 1.0 means a full cylinder of it weighs more than its WC.
- Net and gross weight
- Net is the refrigerant alone. Gross is refrigerant plus cylinder, the number you actually watch on the scale.
Two readings of "80%" the exam punishes
The first wrong reading is pressure. A cylinder holding both liquid and vapor sits at the saturation pressure for its temperature, so the gauge reads about the same whether the cylinder is a quarter full or nearly full of liquid. The limit is about liquid volume, and a gauge can't see volume.
The second wrong reading treats WC as the refrigerant capacity. Water capacity is a volume written in pounds of water. Most liquid refrigerants are denser than water, so 80% of the volume weighs more than 80% of the WC, and adjusting for specific gravity is what turns the stamp into a stop weight. The formula below is industry practice and the usual exam key; it isn't in the rule text of 40 CFR 82 Subpart F (eCFR as of October 5, 2026), while the 80% limit itself is listed under Core safety (EPA test topics, checked October 7, 2026).
A WC 30 lb cylinder, step by step
Read the stamps
WC 30 lb, TW 17 lb. The refrigerant's liquid specific gravity, from the data you're given, is 1.1.
Take 80% of the water capacity
30 × 0.8 = 24 lb. That is the limit for a liquid exactly as dense as water.
Correct for density
24 × 1.1 = 26.4 lb of refrigerant. This is the maximum net weight.
Add the tare
26.4 + 17 = 43.4 lb. Stop recovering when the scale reaches this gross weight.
Maximum net fill at a glance
80% of water capacity, adjusted for liquid specific gravity
| Water capacity | SG 1.0 | SG 1.1 | SG 1.2 |
|---|---|---|---|
| 25 lb | 20 lb | 22 lb | 24 lb |
| 30 lb | 24 lb | 26.4 lb | 28.8 lb |
| 100 lb | 80 lb | 88 lb | 96 lb |
Net refrigerant only; add the stamped tare weight for the scale reading. Formula: WC × 0.8 × SG (industry practice and exam key; not in the rule text).
Do the math
Keep a pencil handy, and write WC, TW and specific gravity down before you calculate anything.
0 right · 0 of 6 answered
What is the proper method for checking if a recovery cylinder is full during the recovery process?
Why each option is right or wrong
Answer: C. Check the cylinder weight to ensure it does not exceed 80% capacity
- AFrost shows that refrigerant is boiling and cooling the cylinder, not how full it is.
- BPressure reflects temperature and refrigerant type, not liquid level, so it cannot show fill.
- CCorrect: weigh the cylinder on a scale and stop before the refrigerant reaches 80% of its capacity (some cylinders also have a float switch).
- DThe sound of the flow says nothing reliable about how full the cylinder is.
Track the fill on a scale. A recovery cylinder shouldn't hold more liquid than 80% of its capacity, which on the scale is water capacity × 0.8 × the refrigerant's specific gravity. The space left lets the liquid expand if the cylinder warms. (Industry practice and exam key, not in the rule text.)
What should be considered when sizing recovery cylinders for a large high-pressure system recovery job?
Why each option is right or wrong
Answer: D. The liquid density of the refrigerant and the 80% fill capacity limit
- AAge matters for a cylinder's retest date, not for how much refrigerant it can hold.
- BPhysical size alone is not enough; how much fits depends on the refrigerant's liquid density.
- CColor identifies a recovery cylinder (gray body, yellow top), not its capacity.
- DCorrect: how many pounds fit depends on the refrigerant's liquid density and the 80% fill limit, so plan enough cylinders for the full charge.
When sizing recovery cylinders for a large high-pressure system, the liquid density of the refrigerant and the 80% fill capacity limit must be considered. High-pressure refrigerants like R-410A have different liquid densities than older refrigerants, affecting the weight capacity of the cylinder.
Why should recovery cylinders never be filled completely with liquid refrigerant?
Why each option is right or wrong
Answer: D. To allow space for thermal expansion of the liquid
- AWeighing is how you control the fill, not the reason for leaving space.
- BLeaving space is not about holding a set pressure; it is about room for the liquid to expand.
- CShipping rules are not the reason; the danger exists even when the cylinder is not being shipped.
- DCorrect: liquid expands as it warms, and with no vapor space left the cylinder can build enormous pressure and rupture, hence the 80% limit.
Recovery cylinders should never be filled completely with liquid refrigerant because liquids expand when heated and could cause the cylinder to rupture if no vapor space is left. The 80% fill rule allows for this thermal expansion.
What is the maximum level to which a recovery cylinder should be filled?
Why each option is right or wrong
Answer: D. 80% of its capacity
- AWrong: a full cylinder leaves no room for the liquid to expand as it warms, which can rupture the cylinder.
- BWrong: 90% still leaves too little vapor space for thermal expansion of the liquid.
- CWrong: 50% is safe but needlessly low; the limit is 80%, not half.
- DCorrect: fill a recovery cylinder to no more than 80% of its capacity so the liquid has room to expand as temperature rises.
Fill a recovery cylinder to no more than 80% of its capacity, leaving room for the liquid to expand as it warms. Capacity means liquid volume; on the scale that is water capacity × 0.8 × the refrigerant's specific gravity.
A recovery cylinder has a 50 lb water capacity. If the refrigerant's specific gravity is 1.2, what is the maximum safe fill weight to avoid venting?
Why each option is right or wrong
Answer: A. 48 lb
- ACorrect: maximum fill = water capacity × specific gravity × 0.8 = 50 × 1.2 × 0.8 = 48 lb.
- B50 lb ignores the 80% limit and leaves too little room for expansion.
- C40 lb applies the 80% limit but leaves out the 1.2 specific gravity.
- D60 lb multiplies by the specific gravity but skips the 80% limit, which would overfill the cylinder.
Maximum fill weight = water capacity × specific gravity × 0.8 = 50 × 1.2 × 0.8 = 48 lb. (Industry practice and exam key, not in the rule text.)
A recovery cylinder has a water capacity of 40 lbs and a tare weight of 18 lbs. Assuming the recovered refrigerant density equals water, what is the maximum allowed gross scale weight?
Why each option is right or wrong
Answer: D. 50.0 lbs
- A32 lb is the maximum refrigerant weight (80% of 40), not the gross weight with the cylinder.
- B46.4 lb does not come from 80% of the water capacity plus the tare.
- C58 lb adds the full 40 lb water capacity to the tare, which would leave no room for expansion.
- DCorrect: 80% of 40 lb is 32 lb of refrigerant, plus the 18 lb tare gives a 50 lb maximum gross weight.
Max safe fill is 80% of water capacity (32 lbs). Adding the 18 lb tare weight gives a maximum gross weight of 50 lbs.
More practice across all four sections: Practice test · Timed mock
Where the 80% limit comes from
Is the 80% fill limit an EPA regulation?
EPA's test topics list never filling a recovery cylinder above 80% as a Core safety point (EPA test topics, checked October 7, 2026). The weight formula itself doesn't appear in 40 CFR 82 Subpart F (eCFR as of October 5, 2026); it's industry practice and the form exam keys use.
Can tare weight alone tell you when the cylinder is full?
No. Tare is only the empty cylinder. The limit comes from water capacity and the refrigerant's density; tare is added afterward to turn that limit into a scale reading. Both stamps, and where they sit, are shown on the recovery cylinder diagram.
Where does the 80% rule sit in the exam?
In the Core section's safety items, next to cylinder types, PPE and pressurizing with nitrogen. The refrigerant safety topic groups them.