Technical Inquiry #21524

This letter is in response to your 1 May 2000 request for information concerning SermaLoy J, a metal coating product. Specifically, you want to know if the use of SermaLoy J produces phosphine gas and, if it does, how the phosphine gas is formed. You further stated that SermaLoy J is a spray applied, heat cured, inorganic slurry which, when heated in a non-oxidizing atmosphere, diffuses to form a silicon aluminide coating on aircraft engine parts.

PRO-ACT contacted Mr. Kevin Eddinger, Quality Assurance Chemist, Sermatech International Inc., (610) 948-5100. Mr. Eddinger stated that the use of SermaLoy J would produce phosphine gas. Metallic phosphide, generated during the heat curing step of the SermaLoy J diffusion process, will decompose into phosphine gas in the presence of water vapor in air. He further stated that we should review the safety recommendations for the diffusion process located on the Material Safety Data Sheet (MSDS) for SermaLoy J, enclosed [NPF 21524.1].

We next reviewed the safety recommendations for the diffusion process located in the MSDS that states:

"The following basic approaches are recommended to eliminate the phosphine hazard.

a. Build or provide a humidity controlled storage enclosure or room that is well ventilated to the outside of the building. This storage area will be used to store diffused parts after removal from the diffusion oven. Its use is essential for the protection of personnel from exposure to phosphine.

Air from the storage area should be exhausted at the rate of at least 2 volume changes per hour and vented in such a manner as to eliminate the possibility of the gas re-entering the building or entering other adjacent buildings.

Experience has indicated that 24 hours is usually sufficient to eliminate most of the phosphine. However, since the hydrolysis of the phosphides is humidity dependent, storage time in excess of 24 hours may be required to eliminate the phoshpine under low humidity conditions. Humidity control is essential to accelerate the formulation of phosphine gas, therefore a humidity (RH) of at least 60 percent should be maintained in the storage area.

b. It is essential that all personnel who are either moving diffused parts from the oven or entering the vented storage area wear pressure demand air line respirators connected to a purified air supply.

d. Signs should be posted to notify all personnel of the phosphine hazard associated with the storage area and the diffusion oven at the time of parts removal.

e. A phosphine detection monitor should be used to detect or monitor the level of phosphine present in the work area and storage area."

We are also providing a copy of the Sermatech International, Inc., Surface Engineering Bulletin J-2, "SermaLoy J," enclosed [NPF 21524.2]. This bulletin provides information on "SermaLoy J," including the application process and safety recommendations.

Finally, we recommend that you coordinate this response with installation occupational health and safety personnel in order to address any concerns they may have associated with this process.