AEDC Model Shop reduces risk with new chemical cleaners Published Aug. 23, 2022 By Jill Pickett AEDC Public Affairs ARNOLD AIR FORCE BASE, Tenn. -- Mission first, safety always. Efforts to put that common saying into action in a meaningful and measurable way came to fruition this summer at Arnold Air Force Base. After more than a year of research and preparation, two new citrus-based chemical cleaners were delivered and put to use in place of hydrofluoric, or HF, acid. "As the Air Force project manager for a project to improve safety in the mission areas, this effort was one of the first I approved to be funded due to its substantial safety impact to personnel and the environment,” said Donna Spry, condition-based maintenance manager with the Arnold Engineering Development Complex 804th Test Support Squadron. “I believe this is one of the most significant improvements I have seen at AEDC in my 17 years." HF acid, a solution of hydrogen fluoride in water, is a corrosive chemical. According to the Centers for Disease Control and Prevention, “Hydrogen fluoride goes easily and quickly through the skin and into the tissues in the body. There, it damages the cells and causes them to not work properly.” In the scheme of risk mitigation, hazard elimination is the most effective, but substitution, which is what was accomplished in the chemical cleaning yard, is considered second in effectiveness. “Considering the hazards associated with HF compared to that of citric acid, this ranks as the most significant example of product substitution I can recall over my 30-plus years in the SHE [safety, health and environmental] field,” said Don Sproul, SHE manager for the Test Operations and Sustainment, or TOS, contractor for Arnold Engineering Development Complex. “This operation has been made substantially safer with this substitution, and all those involved with making it happen should feel very proud of their accomplishment. Improvement opportunities exist all around us. Please continue to build upon this fine example in making AEDC a safer place for everyone.” The journey to replacing the HF acid began when Warner Holt, group manager for Manufacturing Services for the TOS contractor, was speaking with aerospace outside machinists Scottie Stevens, Scott Pogue and Bruce Prater to learn more about their work in the chemical cleaning yard. He had known they work with acids, but speaking with them he learned just how hazardous one of the acids, HF acid, is to people and the environment. “That really got me concerned,” Holt said. “I started doing some research, and that stuff goes through the skin and starts eating bone. It’s very dangerous. You can do damage over time, and it showed pictures of people that had worked with it over the years and the tips of their fingers had worn down where they didn’t protect themselves.” The necessary personal protective equipment and procedures to keep personnel and the environment safe from HF acid exposure were in place, but as long as the HF acid was in use, there was a risk something could go wrong. After meeting with Arnold AFB Fire and Emergency Services and safety on base, a search began for a replacement. “That’s when we started working with the Chem Lab and using their chemical expertise and knowledge,” Holt said. “We said, ‘Hey, we have hydrofluoric acid now and we need something that we can do the same type of cleaning without having to use hydrofluoric acid.” Megan Rawls, a metallurgical lab engineer at the Chemical Laboratory on base at that time, spent several months testing cleaners and identified two citrus-based products that could be substituted for the HF acid. “I am so proud of the teamwork from craft personnel, TOS management, the Chem Lab, along with support from Fire and Emergency Services and TOS Safety to come up with a viable option to replace the HF acid with a much safer alternative,” Spry said. After the substitutes were approved, it took several months of preparation, including removal of the HF acid, which must be handled as a hazardous material even after it is neutralized. Once the new products were in place, the chemical cleaning yard was back up and running, with significantly less risk to the crew that works there. “It’s nice,” said Stevens. “It’s really nice. You put on one of those banana suits [yellow Tyvek suit] and you’ll be ringing wet by the time you walk back there. The heat stress is going to be a lot better to handle now. And, you’re not worried about a pinhole forming in a tank and it blowing the side out while you’re walking by. A catastrophic failure could happen. “The environmental means a lot, too. We don’t want to let anything get out that doesn’t need to get out, so that’s a big plus.” When using HF acid, they had to fully dress out in Tyvek suits, face shields, respirators, rubber gloves and rubber boots because any contact, including inhalation, was hazardous. When using the new products, they only require long sleeves, long pants, rubber gloves and face shields under typical operations utilizing a crane to lift and lower parts into and out of the vats. As far as the environmental safety controls, a liner prevented acid from making contact with the ground in the vat and drying area for parts. The new products do not require that precaution. This reduction in environmental risk allowed for the canceling of a project to reline the drying area, in turn generating a cost avoidance. Other than the risk reduction, the only difference may be a slight increase in the time a part has to stay in the acid to get as clean as with the HF acid. “There could be an argument that it’s not quite as good as the HF, but I’ll take that over exposing these guys to that risk,” Holt said.