Soldered Medical Gas Piping



User Experience Network™ [Health Devices Mar 1995;24(3):127]

Soldered Medical Gas Piping

Medical Gas and Vacuum Systems [18-046]

Hospital

Sections of our medical gas piping installed long ago are joined by lead solder. Does this present any problems or concerns?

ECRI

Before the mid 1980s, most solder contained lead. In water piping, water leaches lead from the solder and presents a risk of lead poisoning, which is why most solders are now manufactured lead-free. In medical gas piping, the gases (e.g., oxygen, nitrous oxide, medical compressed air) do not leach lead from solder and therefore do not present a risk of lead poisoning. However, soldered medical gas piping, regardless of solder type (lead or lead-free), is of concern because solders melt at low temperatures. Thus, if the medical gas piping is exposed to a fire, the soldered joints would open and provide oxygen enrichment to the fire.

Soldered joints present another concern in medical compressed air systems that are poorly maintained. When dehumidification is poor or nonfunctional, water enters the piping. This water can be very chemically reactive, attacking and weakening soldered joints and causing leaks or joint failure. Also, acid flux residue can react with water, causing gaseous and particle contamination. Consistent and proper dehumidification will eliminate these risks, as well as the risks presented by water contamination of the piping. (See our Guidance Article "Medical Gas and Vacuum Systems," Health Devices 23[1-2], January-February 1994.)

Since at least 1970, the National Fire Protection Association's (NFPA) Standard for Health Care Facilities (NFPA 99) and its precursors (e.g., NFPA 56F) have required that medical gas and vacuum system piping be joined by brazing. The brazed joint can withstand the high temperatures of most fires without coming apart. However, this requirement had been obscurely stated and easy to miss; brazing was not clearly and definitively required until the 1993 edition.

Brazing uses a high temperature (i.e., above 1,000° F [538° C]) to melt a brazing alloy, which fills the joint space and holds the pieces together. Soldering works in a similar manner, but uses a soldering alloy, which melts at a low temperature (i.e., below 840° F [449° C]). Solder is easy to nick with a sharp tool; braze metal is not. Soldered joints are also weaker than brazed joints and may leak over time if exposed to vibration (e.g., from pumps, compressors).

Solder-joined piping, which is less expensive to construct than braze-joined piping, was used, inappropriately, in many old medical gas and vacuum systems and was probably overlooked during any inspections of these systems. However, if the piping is breached (e.g., for additions) or requires repair, NFPA 99 and many building codes now require that the soldered joints be replaced. The number of joints to be replaced depends on the governing authority and the specific situation.

In most cases, ECRI advises that soldered joints in medical gas piping be replaced as they become accessible through repair, renovation, or expansion of the building or piping. Also, facilities with soldered medical gas piping should incorporate zone-valve closing in their fire-response plans and training to minimize the fire hazard presented by these joints. (See our Hazard Report "Responding to Fires in Areas of Oxygen Use," Health Devices, 23[7], July 1994, and NFPA 99, Section C-8.3, Suggested Fire Response, Respiratory Therapy.)

Recommendations

1. Replace soldered joints in medical gas piping with brazed joints, as described in NFPA 99, as they become accessible through repair, renovation, or expansion of the building or piping.

2. Incorporate closing of medical gas zone valves in fire-response plans and training, especially in areas where soldered joints exist.

3. Ensure that medical compressed air is dehumidified to a pressure dew point of less than 39° F (4° C) at 50 psi to prevent condensed water from attacking soldered joints.


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