Refrigerant exposure to service personnel or 

DIYers due to leakage of 12 oz charging cans 

or “small cans” 

Experiments Conducted at Honeywell’s 

Research Laboratory in Buffalo, NY USA 

January 2012
Page 2 

Section 1: INTRODUCTION: USE OF 12 OZ REFRIGERANT 

 “SMALL” CANS IN VEHICLE CHARGING 

Twelve ounce charging cans or “small cans” have been used by DIYers and small shops to charge R12 and R-134a automotive systems. These convenient cans can provide improved cooling 

performance and operating efficiency for refrigerant systems that have lost significant charge due to 

hose permeation, compressor shaft seal leakage, and fitting/joint leakage. Although latest generation 

components have significantly lower refrigerant loss rates than older components, there will be a 

loss in charge over the life of the vehicle. A system that is low on charge is not necessarily 

defective; it may be working within its expected engineering design parameters. Since early R-12 

and R-134a systems used accumulators and/or high side refrigerant receivers, these systems had 

large charge plateaus and a “little extra gas” placed into these systems did not typically have 

irreversible effects. States, such as Wisconsin and California, have been restricting the use of small 

cans of 134a due to the high GWP of 134a, and a desire to limit these emissions. Can suppliers have 

begun distributing cans that allow for multiple charges with the same can with re-sealable valve 

cores in the can head. With the can modifications have also come trigger dispensers that may 

include a small charging gauge for more accurate and easy DIY and small professional shop 

charging. Given the low GWP of HFO-1234yf compared to 134a, this rationale for eliminating 

small cans use for HFO-1234yf is non-existent. The changes made to the can due to the 134a 

concerns will also be helpful in minimizing exposure to HFO-1234yf. 

Honeywell has chosen to determine experimentally the actual refrigerant concentrations during DIY 

service leakages in a closed garage with still air. Concentration measurements were collected at 

likely breath locations (not locations buried inside the engine compartment) and still represent very 

conservative DIY exposure during different service scenarios due to the confluence of many 

additional factors present during actual DIY vehicle service, such as cooling fan operation, open 

garage doors (or outdoor environment), movement of the person, wind velocity, etc. We expect 

these experimental measurements to help facilitate aftermarket small can producers to develop 

charging instructions to guide consumers toward successful and safe recharge procedures for 

systems with HFO-1234yf. 

Section 2: CALIBRATION OF EXPERIMENTAL MEASUREMENT DEVICES 

The measurement of refrigerant concentrations was conducted with Henze-Hauck gas sensors 

utilizing a platinum wire to measure the change in thermal conductivity of the gas flowing through 

the measurement cell, Figure 1. As the thermal conductivity of the gas changes as a response to 

refrigerant concentration, the measurement circuit varies the power to the circuit in order to hold the 

temperature of the wire constant. 
Page 3 of 14 

Figure 1. Henze-Hauck Gas Sensor Measurement Principle 

To calibrate the Henze-Hauck gas sensors, a NIST Traceable Environics Series 2000 Gas Mixer 

(S/N 5914900001) with flow repeatability of ±0.05% was utilized. 

Environics Series 2000 Gas Mixer

The Environics Series 2000 contains a library of common industrial gases (air, He, N2, 

hydrocarbons, etc) with a stated accuracy of ±1.0% F.S flow. However, R134a or R-1234zeE was 

not included in the online library and the determination of the gas mixer mass flow controllers was 

necessary. Environics provides a first order estimation of the thermal mass flow meter K-factor 

based on the relationship between gas density and heat capacity. 

ܥ௔௚௦ ൌ 

∑ ܸ௜ܰ௜

௜,௣ܥ௜ܦ௜ܸ ∑

௙௘௥ܰ ൌ௥௘௙ ܥ

௙௘௥,௣ܥ௙௘௥ܦ

ൌ 1.00

1.250 ݃

݈ܿܽ 0.249 כ ݎ݁ݐ݈݅

ܭ‐݃

ൌ 3.215 for Nଶ at STP

K‐factor ൌ

௦௚௔ܥ

௙௘௥ܥ

Where Vi is the volume fraction of each of the gases (R-134a and air), Ni is a factor for the molecular 

structure (monatomic = 1.01, diatomic = 1.00, triatomic = 0.94, polyatomic = 0.88), Di is the density 

of the gas in g/liter at STP (0°C and 101.3 kPa), and Cp,i is the heat capacity of the gas in cal/g-K at 

25 °C and 101.3 kPa. The parameters for R-134a and R-1234zeE are shown in Table 1 along with 

the calculated K-factor. 

Table 1. Environics Gas Mixer K-factor parameters 

Gas Ni Di 

0 °C, 101.3 kPa 

g/liter 

Cp,i 

25 °C, 101.3 kPa 

cal/g-K 

cal. K-factor 

per N2 

0°C, 101.3 kPa 

actual K-factor 

per N2 

0°C, 101.3 kPa 

R-134a 0.88 4.686 0.203 0.287 0.299 

R-1234zeE 0.88 5.260 0.212 0.245 0.261 
Page 4 of 14 

The K-factor was then calibrated by setting mass flow rate (90% of F.S.) and measuring the rate of 

change in the weight as refrigerant was drawn from a cylinder placed atop a NIST traceable MettlerToledo balance with accuracy: ±0.01 g or ±0.03 g/min. Conversion to the gas volume flow rate is 

determined by dividing the balance mass flow rate by the vapor density in Table 1 (for R-134a, ±6 

SCCM). The K-factor was determined by taking the difference between the gas mixer’s indicated 

flow rate and the measured flow rate from the Mettler-Toledo balance, Figure 2 and Figure 3. 

Figure 2. R-134a K-Factor calibration 

K-factor = 0.299 

Figure 3. R-1234ze K-factor calibration 

K-factor = 0.261 

Using the measured K-factor, the flow was measured using the Mettler-Toledo balance for varying 

Full Scale flow settings, Table 2 and Table 3. The measured accuracy for the Environics, using the 

calibrated K-factor for the thermal mass flow controllers, is better than ±1.0% F.S flow. 

Table 2. Flow Calibration For R-134a 

% Full 

Scale Flow Setting 

Measured 

Flow 

Flow SCCM SCCM 

10% 90 94 

20% 180 179 

40% 360 360 

50% 450 451 

60% 540 543 

80% 720 723 

100% 900 904 

Table 3. Flow Calibration for R-1234zeE 

% Full 

Scale Flow Setting 

Measured 

Flow 

Flow SCCM SCCM 

10% 75 71 

20% 150 151 

40% 300 303 

50% 375 372 

60% 450 454 

80% 600 601 

100% 750 748 

Henze-Hauck Gas Sensor

The Henze-Hauck Gas sensor was connected to the output of the Environics Gas mixer. The 

Henze-Hauck sensor contains a small onboard vapor pump to regulate a constant flow rate of 

sample over the sensing element. The total volume flow rate from the gas mixer was set to 3600 

SCCM using dry air with the balance of refrigerant at varying volume % refrigerant flows and 

allowed to flow past the gas sensor for pick by the onboard pump. An automated profile with steps 

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.220.240.260.28

0.3

0.320.340.36

input - measured (g/sec)

K-Factor

-0.010

-0.005

0.000

0.005

0.010

0.230.240.250.260.270.280.29

input - measured (g/sec)

K-Factor
Page 5 of 14 

in concentration was developed to calibrate the Henze-Hauck Gas Sensor over the concentration 

range from 0 vol% to 20 vol% refrigerant, Figure 5. 

Figure 4. Calibration of Henze-Hauck Gas Sensor 

Figure 5. Calibration profile for HenzeHauck Gas Sensor Figure 6. Typical Calibration Curve for 

Henze-Hauck Gas Sensor 

During calibration it was noted that the Henze-Hauck sensors are sensitive enough to detect 

changes in air relative humidity. While a calibration for humidity was not performed due to the 

nature of intended testing, for long term testing it may be necessary if large humidity variations are 

expected. For the intended testing, it became convenient to treat the air conditions as a constant 

offset to the measured mV output of the sensor circuit. A typical steady state calibration curve is 

included as Figure 6. The calibration is essentially linear output response to concentration; 

however, there is a small, repeatable curvature. Using the accuracy of the Environics Gas Mixer, 

the reportable accuracy of the Henze-Hauck Gas Sensor over the range 0 vol% to 20 vol% 

refrigerant for R-134a and R-1234zeE is better than ±0.2 vol%. 

Environics Series 2000

Gas Mixer

Air

or

N2

Gas

1

Gas 

2

Gas 

3

Output

Exhaust

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Refrigerant Concentration, vol%

Time, min 0

5

10

15

20

25

30

35

0% 5% 10% 15% 20% 25%

Airoffset - Sensor Output, mV

Refrigerant Concentration, vol%

y = 3.846e-6*x2 + 0.00610*x

R2 = 0.999
Page 6 of 14 

Refrigerant concentration testing generally involves accident scenarios where large amounts of 

refrigerant are released in relatively short periods of time. Therefore, the time response of the 

Henze-Hauck sensor was also evaluated as a simple electrical RC circuit analogy: 

߬

ሻݐሺ௥ݒ݀

߬ ൌ ሻݐሺ௥ݒ ൅ ݐ݀

ሻݐ௦ሺݒ݀

ݐ݀

ݒ௥ሺݐሻ ൅ ݒ௖ሺݐሻ ൌ ݒୱሺݐሻ

reducing develops the relationship between measured (indicated) concentration and actual 

concentration. 

ݒୱሺݐሻ ൌ ߬

ሻݐሺ௖ݒ݀

ሻݐሺ௖ݒ ൅ ݐ݀

Where vs is the real gas concentration that is measured, vc is the measured sensor output, τ is the 

time constant, and t is time. To determine the time constant, τ, the large step change in 

concentration from 10 vol% to 0 vol%, Figure 7, was taken from the calibration profile. For 

determination of the time constant, the above equation can be solved as: 

ݒܿ ൌ ݒܿ,݋ ቆ1െ݁൬

ݐെ

߬ ൰

ቇ

Where vc,o is the steady state sensor output. The time constant experienced with most of the HenzeHauck sensors is approximately 14 seconds. 

Figure 7. Henze-Hauck time constant determination

0

2

4

6

8

10

12

14

16

18

-50 0 50 100 150 200 250 300

Change in Sensor Output, mV

Time, sec

Exp. Data

fit

τ = 14 sec
Page 7 of 14 

Section 3: SETUP OF CONCENTRATION TESTS

A 1995 Toyota Corolla was used for experimental measurement of refrigerant concentration during 

and after small can leakage scenarios. All tests were conduced in a small enclosed garage with no 

air movement since an outdoor test or normal air movement would work to speed dilution of the 

refrigerant from the measurement area and lower concentrations. The air conditioner (engine 

running) must be on for practical servicing of the AC system; however, we did tests with the 

condenser fan on and off to investigate how quickly the fan dissipates the refrigerant. Only full can 

punctures of 3 mm (worst case) were investigated. Leakages took place at the low side service port 

near the firewall located on the passenger side as this would be the location of 

connection/disconnection of cans to service the AC system (Figure 8). Different leakage scenarios 

were investigated covering the range of can releases from half-can, full-can to double-can in both 

inverted and upright. We also found that the hood height made a difference in the refrigerant 

concentrations so a half height hood support was constructed to increase the refrigerant 

concentration. The testing matrix and summary of measurement results is shown as Table 4. 

Table 4. Small Can Engine Leakage Test Conditions 

Test 

# 

Can Charge Can 

Position 

Hood 

Position 

Condenser 

Fan 

Peak Breath

Conc. 

30 min TWA 

Peak Floor Conc.

30 min TWA 

1 Full 

340 g (12 oz) Inverted Open Full On 0.3 vol% 46 ppm 

1.3 vol% 

228 ppm 

2 Full 

340 g (12 oz) Inverted Open 1⁄2 On 0.7 vol% 224 ppm 

1.7 vol% 

302 ppm 

3 Full 

340 g (12 oz) Inverted Open 1⁄2 Off 0.7 vol% 119 ppm 

2.7 vol% 

376 ppm 

4 2 cans, Full 

680 g (24 oz) Inverted Open 1⁄2 Off 0.2 vol% 201 ppm 

3.0 vol% 

1,030 ppm 

5 Half 

170 g (6 oz) Upright Open 1⁄2 Off 0.1 vol% 183 ppm 

1.2 vol% 

1,312 ppm 

6 Full 

340 g (12 oz) Upright Open 1⁄2 Off 0.5 vol% 915 ppm 

1.5 vol% 

1,789 ppm 

Measurements were taken with the calibrated Henze-Hauck refrigerant concentration sensors with 

an accuracy of 0.2 vol% refrigerant in air. Data was collected every 3 seconds from the initiation 

of the leak to a final time where the refrigerant has completely dispersed. Refrigerant samples were 

also taken under the engine compartment representing a worker on a creeper with breath location, 

15 cm (6 in) off the floor on the driver and passenger side (Figure 9). Refrigerant collection was 

also taken at the breath locations on the driver and passenger side were a person servicing the 

system would have their head located while bent over the engine (Figure 10 and Figure 11). 

Additional measurements were located at the front bumper 30 cm (12 in) off the ground 

representing a person servicing the front of the vehicle. 
Page 8 of 14 

Figure 8. Refrigerant Leak at Low Side 

Service Port 

Figure 9. Refrigerant Sampling under 

engine 

Figure 10. Refrigerant Sampling Passenger 

Side Breath with hood 1⁄2 open. Technician 

pictured to show relative breathing location 

for scenario. 

Figure 11. Refrigerant Sampling Driver Side 

Breath with hood 1⁄2 open. Technician 

pictured to show relative breathing location 

for scenario. 

Section 3: RESULTS 

1) Hood Position (Full open or half) – Lowering the hood to a position of 1⁄2 that of the 

manufacturers original support rod length increased the refrigerant concentration at both the 

above engine and below engine sampling ports. Figure 12 shows a full, inverted can (fast 

release) being discharged as a person is servicing the AC system with the hood resting on the 

manufacturers support and the condenser fan on. Figure 13 shows the same test with the hood 

open half and the face locations receiving an increase of refrigerant exposure. The front 

bumper concentration decrease and under engine concentration increase measurements 

demonstrate the effect of the hood directing the flow of air through the engine and out the rear 

of the vehicle reducing recirculation. Regardless of the hood position, the worst case 30 minute 

time weighted average exposure was 302 ppm with the condenser fan on. 
Page 9 of 14 

Figure 12. Test Case #1, full, inverted can (340 g) released at LS Service Port with hood 

fully open and condenser fan on.

Figure 13. Test Case #2, full, inverted can (340 g) released at LS Service Port with hood 

half open and condenser fan on. 

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 57 ppm

Front Ground, Driver-Center 75 ppm

Front Ground, Pass-Center 211 ppm

Front Ground, Passenger Side 228 ppm

Driver Side Under Engine 43 ppm

Passenger Side Under Engine 50 ppm

Passenger Side Worker Face 46 ppm

Driver Side Worker Face 44 ppm

30 Min TWAs

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 86 ppm

Front Ground, Driver-Center 94 ppm

Front Ground, Pass-Center 92 ppm

Front Ground, Passenger Side 79 ppm

Driver Side Under Engine 302 ppm

Passenger Side Under Engine 277 ppm

Passenger Side Worker Face 174 ppm

Driver Side Worker Face 224 ppm

30 Min TWAs
Page 10 of 14 

2) Condenser Fan (On or Off) – Turning the condenser fan off greatly reduced the flow of air 

available to disperse the refrigerant from the proximity of the engine. Since the refrigerant 

vapor is 4x heavier than air, the leaked vapor has the tendency due to buoyancy to flow down 

through the engine and disperse on the ground. Figure 14 shows that versus test case #2 with 

the condenser fan on, the refrigerant concentrations below the engine increased and the breath 

concentrations of a worker above the engine increased. The peak concentration of a worker 

under the vehicle while service was carried out above the vehicle would be exposed to 376 ppm 

for a 30 minute time weighted average if they are laying directly on the ground or creeper. 

Figure 14. Test Case #3, full, inverted can (340 g) released at LS Service Port with hood 

half open and condenser fan off. 

3) 2 Full Cans – While improbable that a repair scenario exists where two full cans are rapidly 

discharged, refrigerant concentration measurements were carried out to determine the exposure 

with the condenser fan off and the hood in the 1⁄2 open position. The cans were released as 

quickly as making the connection to the second can would allow (about 1 minute). Figure 8 

shows the time weighted averages increased due to the additional, second can, and the worst 

case 30 minute average was approximately 1000 ppm under the engine and the worker breath 

location above the engine was 202 ppm.

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 136 ppm

Front Ground, Driver-Center 164 ppm

Front Ground, Pass-Center 345 ppm

Front Ground, Passenger Side 171 ppm

Driver Side Under Engine 376 ppm

Passenger Side Under Engine 180 ppm

Passenger Side Worker Face 120 ppm

Driver Side Worker Face 115 ppm

30 Min TWAs
Page 11 of 14 

Figure 15. Test Case #4, full, inverted cans (2 cans, 680 g) released at LS Service Port with 

hood open half and condenser fan off. 

4) Upright leakage (half and full can) – For refrigerant cans that do not employ a resealable 

connection or valve, it may be expected that in the process of charging a system the entire 

contents of the charging can will not be used and some refrigerant will remain. We investigated 

the refrigerant concentrations for a can in which half the contents were removed prior to 

leakage, and for a can which was fully punctured and then set aside. For these cases the 

leakage times increased dramatically from the inverted tests, as the leakage rate is a function of 

the amount of heat that can be transferred to the can from the surroundings. In our tests the 

garage was at 20oC (68 ̊F). The test shows the release as the can is opened and the pressure 

drops, chilling the can to a lower release rate due to reduced internal can pressure. In the case 

of the half can, the leak continued for approximately 20 minutes to release the contents and the 

30 minute time weighted averages (Figure 16) were 1,312 ppm for a worker under the engine 

laying on the ground or creeper, and 183 ppm for a worker bent over the top of the engine. For 

the full can release the leakage took approximately 1 hour to complete and the 30 minute time 

weighted averages (Figure 17) were 1,789 ppm for a worker under the engine laying on the 

ground or creeper, and 916 ppm for a worker bent over the top of the engine.

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 264 ppm

Front Ground, Driver-Center 418 ppm

Front Ground, Pass-Center 608 ppm

Front Ground, Passenger Side 389 ppm

Driver Side Under Engine 1,030 ppm

Passenger Side Under Engine 758 ppm

Passenger Side Worker Face 202 ppm

Driver Side Worker Face 169 ppm

30 Min TWAs
Page 12 of 14 

Figure 16. Test Case #5, half, upright can (170 g) released at LS Service Port with hood half 

open and condenser fan off. 

Figure 17. Test Case #6, full, upright can (340 g) released at LS Service Port with hood half 

open and condenser fan off. 

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 322 ppm

Front Ground, Driver-Center 158 ppm

Front Ground, Pass-Center 49 ppm

Front Ground, Passenger Side 489 ppm

Driver Side Under Engine 204 ppm

Passenger Side Under Engine 1,312 ppm

Passenger Side Worker Face 183 ppm

Driver Side Worker Face 12 ppm

30 Min TWAs

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 4200 4500

Time, seconds

Refrigerant Conc, vol 

%

Front Ground, Driver Side 226 ppm

Front Ground, Driver-Center 376 ppm

Front Ground, Pass-Center 505 ppm

Front Ground, Passenger Side 511 ppm

Driver Side Under Engine 335 ppm

Passenger Side Under Engine 1,789 ppm

Passenger Side Worker Face 916 ppm

Driver Side Worker Face 210 ppm

30 Min TWAs
Page 13 of 14 

Section 4: CONCLUSIONS 

Exposure levels measured in our testing show that DIY servicing from 12 oz cans 

would not result in exposure levels determined to be unsafe by EPA. EPA sets the single 

exposure Human Equivalent Concentration (HEC) limit for 1234yf at 98,211 ppm and 

recommends a margin of exposure (MOE) of greater than 30.1

Acute exposure MOEs will be derived from the HEC determined from the rat 

studies ... The HEC of 98,211 ppm will be divided by the predicted exposures to 

derive the MOE. 

To determine the MOE for 1234yf, EPA adopted the box modeling results of the SAE 

CRP Final Report,2 which was intended to be a highly conservative screening analysis of 

possible repair exposures. Dr. Lewandowski3 correctly points out that the rationale for using 

the box model is to determine whether, even if using worst‐case assumptions, the risk 

estimates are acceptable, so that more detailed risk characterization effort is unnecessary. 

Because the box model is a screening model, the appropriate response to box modeling 

results that do not demonstrate the risks are acceptable is to undertake more sophisticated 

and sensitive tests to determine whether in fact the concentrations are below levels of 

concern. 

EPA’s box modeling found an acceptable MOE for any of the exposure scenarios except 

for the inverted can release scenario. Honeywell’s testing shows, however, that the box 

model estimates do not accurately characterize the risk of exposure when servicing is 

performed with inverted cans. Using the box model, the SAE CRP Final Report found that the 

upright can generated a 30 minute time‐weighted average (TWA) of 2,493 ppm and the 

inverted can generated a 30 minute TWA of 32,800 ppm inside the 0.5 m3 engine 

compartment. Our testing of the upright can found that the box model may be justified as an 

approximation for the very slow release of can contents, which we measured at 1,789 ppm. 

However, in the cases of inverted can releases, our results do not correlate to the 

assumptions of the box model. Refrigerant buoyancy and induced ventilation by the 

refrigerant release resulted in a much lower 30 min TWA for the inverted can (32,800 ppm 

predicted vs. 376 ppm for a single can and 1,030 ppm for full discharge of two cans). Thus, 

our test data shows a much higher MOE for inverted can release than predicted by the box 

model. The results are shown below in Table 5 in terms of the predicted MOE, compared to 

the measured MOE. 

 

1

 “Risk Assessment Addendum for the EPA,” EPA-HQ-OPPT-2008-0918-0080 or EPA-HQOPPE-2008-0918-0034 

2

 EPA-HQ-OPPT-2008-0918-0078 

3

 EPA-HQ-OAR-2008-0664-0091 
Page 14 of 14 

Table 5. MOEs for Different Leakage Scenarios 

30 min TWA 

(ppm) 

MOE derived from 

EPA HEC single 

exposure value of 

98,211 ppm 

Inverted Can Release 

SAE 1234CRP Final Report: Gradient report 

32,800 

(est. box model) 3 

Upright Can Release 

SAE 1234CRP Final Report: Gradient report 

2,493 

(est. box model) 39 

Inverted Can Release 

Honeywell Vehicle Testing 

Two cans: 1,030 

One can: 376 

(measured) 

95 

260 

Upright Can Release 

Honeywell Vehicle Testing 

1789 

(measured) 55 

EPA recommends a MOE of greater than 30 for HFO‐1234yf. As Table 1 illustrates, the 

actual MOE for small can servicing ranges from 55 to 260, well to the safe side of the 

acceptable risk levels recommended by EPA. 

Contact Information: 

Dr. Christopher Seeton 

Christopher.Seeton@honeywell.com 

20 Peabody Street 

Buffalo, NY 14051