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Tuesday
Apr032012

Patination

There have been a number of issues surrounding the use of metallurgic color “patinas” as indicators for a hazardous material contained in an inappropriate container. While detection devices are wrought with precision and accuracy issues, metallurgical changes resulting in color and structural weakening are consistent. While this may be a crude detection device it can assist the decision making process “without” exposing entry personnel to a total unknown. The evaluation of hazardous materials can take a variety of forms. Do not be too quick to dismiss older techniques where safety is concerned. It is important to understand the history of this science to enhance your “knowledge of perspective” when making hazardous materials response decisions.

“Patination” is the process of subjecting materials to chemicals and “recipes” to change the visual appearance of an object. Whether it is mechanical through “distressing” wood, or changing the finish and color of metals from chemical applications, the desired result is to enhance the objects beauty. Natural “patination” by exposure to the elements with time is what increases an antiques value. However, some natural patination, such as rusting can deteriorate and weaken materials.  Natural or man-made, patination becomes a safety issue when it affects equipment preventing the uncontrolled release of hazardous materials. Proper care of transfer piping, equipment, and compatibility issues prevent metallurgical weakening and potential uncontrolled releases.

When agricultural or industrial chemicals are stored improperly, the “patination” of inappropriate containers, valves, or piping may result. While this is a good indication of chemical contamination usually involving criminal theft, {see other anhydrous ammonia articles} internal stress fractures can exist and be unseen from the vessels exterior. The only indication for the responder in the case of anhydrous ammonia is a resulting "blue-ish" silver “patina” color to the brass non-ferrous valve assemblies seen on common 20 lb. gas grill bottles. Such is the case as these containers frequently turn up on methamphetamine drug labs containing anhydrous ammonia. The corrosive effect on the transfer manifold serves to “leachate” the inherent strength out of these cast brass fittings. Cross sections of these appurtenances demonstrate this by exhibiting longitudinal cracking along the length of the manifolds interior body. This condition has failed the manifold body on several occasions, even with careful responder handling. An uncontrolled release of a 20 lb. cylinder with an approximate expansion rate of 250 times per square feet of area, will result in an atmospheric contamination of approximately 5000 square feet. When the decision to “sparge” has been made by incident command, prepare your “sparge” system BEFORE moving the cylinder into the “sparge” position. This will safeguard against an uncontrolled release, and possible injured responders.

Proper anhydrous ammonia equipment appurtenances bodies are generally constructed of durable ductile iron. Moving pieces, such as valves and stem pieces for opening and closing the valve are done in stainless steel to resist corrosion. Finally, the seals and gaskets are finished in Buna-N, Teflon, Nylon, or Neoprene materials for the same issue. Compatibility “against” the corrosive forces of anhydrous is the main goal. This feature gives the valve long and safe usage under hazardous conditions. When the “Safety of construction” rules are ignored by criminals, accidents and hazardous material leaks are invited. Hence, this is when we are called to the scene. The uncontrolled release of this product has its greatest affect on the respiratory system. Severe dermal burns result if unprotected tissue comes into close contact with anhydrous ammonia vapors. There has been conversation regarding the flammability of this product, but these levels are generally controlled by the inevitable ventilation of the released product from a confined area. Therefore, since high concentrations of the “liquifacted” product are flammable ventilation is a must. Since this gas boils at room temperature, ignition inside a pressure container is seldom seen.

                                                    Haz Mat Mike

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