HAZARDOUS GAS CYLINDER CHANGE PROCEDURE
The intent of this document is to describe a typical gas bottle change out procedure without limiting the scope to specific gas; in other words, a general procedure suitable for all hazardous gasses.
Hazardous gas cylinders have been sized to minimize the number of bottle changes over a given frequency. This is done to account for the fact that bottle changing represents the greatest risk for accident or injury. In most cases, gas cylinders will last one year or longer.
IMPORTANT: Consult the gas manufacturer’s SDS prior handling any hazardous gasses.
Note: One should be thoroughly familiar with gas cabinet operation prior to undertaking a gas cylinder change. Consult the operations manual prior to undertaking any gas cylinder operations.
The following gasses to be used in the CEPSR cleanroom are known to have health and safety hazards associated with them (in many cases, the gasses will have multiple hazards): Chlorine, Dichlorosilane, Ammonia, Boron Trichloride, Acetylene, Hydrogen, Methane, Silane, Nitrous Oxide, Difluoromethane, and Oxygen.
Overview- It will be assumed there is a gas cylinder in service at the start of this procedure. Even if there is not, it is good practice to follow this process as it will ensure all gas line are void of contaminates and hazards prior to connecting a gas cylinder.
The process can be broken down in to four steps: The evacuation of gas lines, the removal of the spent cylinder, the installation of the new cylinder, and placing of the new cylinder in service.
The gas cylinder change procedure requires two trained persons at minimum.
1. Evacuation of gas lines
a. Close the cylinder manual isolation valve.
b. Gas cabinets will have an automated pump/ purge cycle that will sweep and purge all hazardous gasses from the gas delivery lines. The number of cycles can be set by the user. The Columbia University clean room will use 20 cycles. The purge gas is 90% Nitrogen (N2) with 10% Helium (He).
2. Removal of the spent gas cylinder.
a. Disconnect the CGA fitting from the cylinder manual isolation valve. Take care to note the connection type as some gas cylinders will be reverse threaded.
b. It is important to take measurements for hazardous gasses at the cylinder isolation valve at this time. Breaking and resealing the CGA fitting will allow minimal exposures until it can be confirmed that no hazardous gasses are present.
c. When the CGA fitting has been opened a small amount of N2/He will emit from the gas cabinet side. This is desired as it will keep air and other unwanted contaminates from entering the gas delivery system.
d. Place the protective cap on the cylinder.
e. The cylinder is now safe for transport to the designated transfer location. Cylinders will only be transported on gas cylinder carts. Carts must be equipped with a device that will hold the cylinder secure.
f. The driver will receive the cylinder from the clean room staff and secure it to the appropriate transport device.
3. Installation of new gas cylinder.
a. Clean room staff will receive the gas cylinder from the delivery driver and place the cylinder on the cylinder transport cart.
b. Install the new cylinder into the gas cabinet and secure in to place.
c. Remove the protective cap from the cylinder isolation valve. The valve will be covered with a plastic seal. This should be removed as well. If this plastic seal is missing, contact the gas vendor immediately. Do not install this gas cylinder.
d. The installation of a new gas cylinder will require the replacement/ installation of a new sealing gasket. Clean the sealing surfaces of the male and female CGA fittings prior to installing the gasket. Install the sealing gasket.
e. Tighten the CGA to manufacturer’s specification.
f. He leak checking- The cleanroom staff will perform helium leak checks during the installation of hazardous gasses prior to opening the cylinder isolation valve. The gas manifold will be pressurized with helium from the cylinder isolation valve to a point down stream of any fittings disturbed during gas cylinder change operations. All fittings disturbed during these operation will be analyzed for leaks. This will be performed using the on-board 10% He/ 90% N2 purge cylinder. By utilizing this method there will be no disruption of fitting subsequent to performing the Helium leak check.
4. Placing the new cylinder in service
a. It is now safe to open the cylinder isolation valve.