STANFORD UNIVERSITY

COMPRESSED GAS LEAK TEST PROCEDURE

31 July 1998

At Stanford University, all toxic gas cylinders will be tested for leaks prior to removing cylinders from the delivery vehicle, if possible. Also, non-toxic gas cylinders such as flammables should be tested for leaks before acceptance. Leaking gas cylinders will not be accepted. The Principal Investigator (PI) who ordered the gas cylinder is responsible for ensuring that the cylinder is leak tested. Similarly, all compressed gas experimental apparatus should be leak tested periodically per the applicable experimental protocol. Only individuals trained in the use of leak detection methods should perform this leak test procedure.

Leak Detection Methods: The preferred and primary method for leak detection is a direct reading instrument with a sensor that uses thermal conductivity different from that of the ambient air for detection, such as the Matheson LeakHunter Plus Model 8066 or its equivalent. This type of detector is highly sensitive and can locate leaks too small to bubble quickly with a liquid solution leak detector.

 

Gases and vapors with thermal conductivity different from air can be detected with this method, and some are listed below in Table 1.

 

TABLE 1. Gases and Vapors Detected by the Conductivity Different from Air Method

Gas

Detection limit

ACGIH TLV TWA (ppm)

Acetone

10 cc/min

500

Ammonia

5 ppm

25

Arsine

0.3 ppm

0.05

Benzene

10 cc/min

0.5

Carbon Monoxide

1 ppm

25

Chlorine

7 ppm

0.5

Diborane

0.15 ppm

0.1

1,1-Dichloroethane

10 cc/min

100

Ethanol

10 c/min

1000

Ethylene

1 cc/min

N/A

Ethylene Oxide

350 ppm

1

Formaldehyde

10 cc/min

C 0.3

Freon 12

1 cc/min

1000

n-Hexane

10 cc/min

50

Hydrogen

10 ppm

N/A

Hydrogen Bromide

1 ppm

C 3

Hydrogen Chloride

1 ppm

C 5

Hydrogen Selenide

0.5 ppm

0.05

Hydrogen Sulfide

1 ppm

10

Isopropyl Alcohol

10 cc/min

400

Methane

1 cc/min

N/A

Methyl Bromide

40 ppm

1

Methyl Chloride

50 ppm

50

Methyl Ethyl Ketone (MEK)

10 cc/min

200

Phosphine

0.13 ppm

0.3

Propane

1 cc/min

2500

Silane

0.3 ppm

5

Sulfur Dioxide

1 ppm

2

Toluene

10 cc/min

50

Trichloroethylene

10 cc/min

50

Vinyl Chloride

10 ppm

5

Xylene

10 cc/min

100

 

An alternate method, if the primary method cannot be used, is liquid solution leak detection such as the Matheson Detect-A-Leak™ or equivalent that meets or exceeds MIL-L-25567D Type I and II specifications.

 

CYLINDER DELIVERY LEAK TEST PROCEDURE:

  1. With the cylinder on the delivery vehicle, visually inspect the cylinder for cap, proper labels, dents, excessive rust, pitting, or other physical damage.
  2. Following the calibration and operation procedures for your detector, insert the probe of an operational detector through the cap slots and sample for at least 2 seconds or 2 times the response time, whichever is longer.
  3. If the cylinder cap does not have slots (remove the cap) or the cylinder does not have a cap, slowly move the probe around the neck of the cylinder or apply the leak detection solution to likely leak locations, following the directions on the container.
  4. If a leak is detected, leave the cylinder on the delivery vehicle for immediate return to the vendor.
  5. If the leak prevents the delivery vehicle from leaving, immediately call 9-911 and evacuate to a safe proximity location to wait on the arrival of emergency responders.

 

OPERATIONAL LEAK TEST PROCEDURE:

  1. Visually inspect the cylinder and experimental apparatus for proper labels, dents, excessive rust, pitting, bent lines, disconnected lines or other physical damage.
  2. Following the calibration and operation procedures for your detector, place the probe of an operational detector near possible leak points such as connections, valves, manifolds, panels, pressure gages of a pressurized system for at least 2 seconds or 2 times the response time, whichever is longer, or apply the leak detection solution to likely leak locations, following the directions on the container.
  3. If a leak is detected, immediately shut off the supply of gas at its source and perform maintenance to stop the leak. Do not use a toxic or flammable gas in the experimental apparatus until the system has been pressure leak tested with an inert gas per the applicable standard operation procedure (SOP) for the experiment.

 

CYLINDER RETURN LEAK TEST PROCEDURE:

  1. With the cylinder in an appropriate exhausted enclosure such as a gas cabinet or fume hood, visually inspect the cylinder for cap, proper labels, dents, excessive rust, pitting, or other physical damage.
  2. Following the calibration and operation procedures for your detector, insert the probe of an operational detector through the cap slots and sample for at least 2 seconds or 2 times the response time, whichever is longer.
  3. If the cylinder cap does not have slots (remove the cap) or the cylinder does not have a cap, slowly move the probe around the neck of the cylinder or apply the leak detection solution, following the directions on the container.
  4. If a leak is detected, immediately call the vendor to arrange for the cylinder to be removed.
  5. If the cylinder is not in an exhausted enclosure and the leak prevents the cylinder from being moved, immediately pull the nearest fire alarm and evacuate to a safe emergency assembly point (EAP) to wait on the arrival of emergency responders.

For additional resources related to toxic gases, consult the EH&S TOXIC GAS ORDINANCE AT STANFORD , or call 3-0448 for EH&S assistance.