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]
Sections of our medical gas piping installed long ago are joined by lead
solder. Does this present any problems or concerns?
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, July 1994, and NFPA 99, Section C-8.3,
Suggested Fire Response, Respiratory Therapy.)
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.