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Reaffirmed November 2012
Plumbing Manufacturers International (PMI), the trade association of plumbing product manufacturers, has made the promotion of water efficiency a top priority and has included it in its mission statement. PMI’s members are the industry leaders in producing innovative water efficient plumbing technologies relied upon to meet indoor water conservation goals.
PMI’s commitment to water efficiency includes promoting the development and use of higher efficiency showerheads and hand held showers (showerheads and hand held showers that use less than the 2.5 gallons per minute mandated by Federal law). Higher efficiency showerheads and hand held showers represent a promising opportunity to conserve water.
PMI is also committed to ensure that the needs of Manufacturers, Environmentalists, and Consumers are addressed. There is a need to make sure that the manufacturers can deliver a product that can accomplish the water savings required, while at the same time ensuring there is sufficient water to carry the waste to its final destination. They must do all this while providing a safe and pleasurable showering experience for the consumer. To address these needs, PMI and other industry stakeholders continue working through a joint effort between the American Society of Sanitary Engineers (ASSE), the American Society of Mechanical Engineers (ASME) and the Canadian Standards Association (CSA) to develop requirements that address acceptable shower efficiency without compromising performance or safety. This effort is being channeled through a tri-lateral standard. (ASSE 1016-2011/ ASME A112.1016-2011/CSA B125.16-11, Performance Requirements for Automatic Compensating Valves for Individual Showers and Tub Shower Combination) The resultant criteria will help to ensure showerheads and hand held showers perform as intended, and serve as a critical resource for regulators, water providers and fellow efficiency advocates who are developing water efficiency and green building guidelines.
With regard to bather safety, PMI believes it is important for installers and users to understand there is an increased potential for bathing hazards known as thermal shock and scalding with the use of higher efficiency showerheads and hand held showers. The potential risks may be further magnified in existing plumbing systems without the protection of automatic compensating shower valves designed to reduce these risks if installed prior to code requirements.
WHAT ARE THERMAL SHOCK AND SCALDING AND WHAT ARE THE CONSEQUENCES?
It is widely understood that exposure to hot water or a sudden unanticipated change in water temperature in the shower can present a hazard. Thermal shock is a sudden and unanticipated change in water temperature which can cause an abrupt physical reaction of a person, resulting in a serious injury from a slip, fall or scalding. The rapid temperature changes can be either toward colder or hotter water. These changes are caused by simultaneous usage of other fixtures on the same hot and cold water distribution system such as a toilet, or an appliance such as a dishwasher or clothes washing machine, that demands a large quantity of water, quickly. This creates a pressure imbalance between the hot and/or cold water supply at the shower. The imbalance changes the ratio of hot and cold water, which leads to a change in outlet temperature. If the temperature change to hotter water is great enough, it can also result in scalding.
LOWER FLOW SHOWERHEADS INCREASE THE RISK OF THERMAL SHOCK AND SCALDING
In general, showerheads with lower flow rates tend to make the plumbing system more sensitive to the pressure changes created when other fixtures are operated while the shower is being used. This increased sensitivity can result in rapid temperature changes of larger magnitude and longer duration and the increased risk of thermal shock and scalding. The reason for the increased sensitivity is because Automatic Compensating Shower Valves which comply with ASSE 1016-2011/ASME A112.1016-2011/CSA B125.16-11 are sized to compensate for hot or cold inlet temperature or pressure changes at a given showerhead or hand held shower outlet flow rate. When retrofitted with a showerhead, hand shower or outlet with a lower flow rate than the Standard calls for, the risk of thermal shock or scalding is increased. Automatic Compensating Valves exercise their control capability by creating a pressure drop across the control valve mechanism. When a lower flow rate outlet is used, it ends up taking more of the pressure drop across the outlet, in effect reducing the pressure drop across the control valve mechanism and significantly compromising its ability to compensate for inlet pressure changes.
When various states and the federal government were implementing laws to reduce the showerhead flow rates to 2.5 gallons per minutes in the early 1990’s, PMI led the plumbing industry in updating and implementing product standards and plumbing code requirements to mitigate the risks of temperature-related shower injuries exacerbated by lower flow showerheads. As a result, the vast majority of plumbing codes throughout the United States and Canada now require individual automatic compensating valves complying with either ASSE 1016 or ASME A112.18.1/CSA B125.1 to provide thermal shock and scald protection in the shower. It is important to note that these product standards and plumbing codes assume that an automatic compensating valve is serving a 2.5 gpm showerhead or hand held shower and do not assure that it is sensitive enough to provide thermal shock and scald protection at lower flow rates. The latest harmonized standard ASSE 1016-2011/ASME A112.1016/CSA B125.16-11 also requires the manufacturer of the valves to state the minimum flow rate for the showerhead and hand held shower at which the valve will still perform.
Manual Flow Reduction/Shut-Off Valves
Another area of potential water savings identified is to have water flow reduction and / or positive shut-off valves on showerheads and hand held showers. The object is to reduce flow below the rated flow (2.5gpm) during soaping and lathering periods. The shower is returned to full flow after the soaping period. Use of any device that will reduce or shut off the flow to a showerhead or hand held shower may result in cross flow. This situation can cause thermal shock and scalding issues.
With regard to bather safety, PMI believes it is important for installers, users, and regulators to understand there is an increased potential for cross flow of hot or cold water during the period of reduced flow if these flow reduction or flow shut-off measures are adopted. PMI has maintained that any flow through a two handle or single handle shower valve, regardless of whether that unit is an automatic compensating valve or not, may result in a dangerous cross flow unless there are check valves installed on the inlets or are integral to the shower valve. The cross flow may occur because the reduced shower flow or shut-off puts back pressure to the valve from the showerhead or hand held shower. During periods of back pressure the hot water may overtake the cold water, especially if there is any demand on the cold water system during that period. In addition there can be a cross flow from cold to hot when the same condition exists and there is a hot water demand elsewhere in the system. The demand on the cold water system elsewhere may cause the cold water pressure to the valve to drop, creating a situation where the hot water pressure is now greater that the cold. When there is a situation of higher pressure on the hot side and a lack of release through the outlet, showerhead, or hand held shower, the hot water will fill the cold water supply line. This creates a situation where there is now hot water in the supply of both the hot and cold sides of the valve. The same will happen from cold to hot when the demand is on the hot water system.
The results of such a cross flow is that the bather will feel full hot water (or cold water) through the showerhead or hand held shower for a period of time. The amount of time will be dependent on the type of valve, the amount of back pressure, and the length of the disturbance. (It is not uncommon that some people will utilize the shut-off valve to the showerhead or hand held shower as the final shut-off of the valve. This could result in hot water showing up in the toilet or kitchen faucet). Needless to say the effect on the bather will be extremely dangerous and potentially life threatening.
WHAT SHOULD BE DONE
PMI believes that the most effective way to minimize the risk of scalding and thermal shock is to ensure that acceptable methods of controlling water temperatures are installed when installing showerheads and hand held showers.
In new construction and renovated plumbing systems, the shower should be equipped with an automatic compensating valve that complies with ASSE 1016 or ASME A112.18.1/CSA B125.1 or the new ASSE 1016-2011/ASME A112.1016/CSA B125.16-11 standard and is specifically designed to provide thermal shock and scald protection at the flow rate of the showerhead and hand held showers being used.
Existing shower valves without protective features provide no thermal shock or scald protection. As such, the shower valve should be replaced with an automatic compensating shower valve complying with ASSE 1016 or ASME A112.18.1/CSA B125.1 or the new ASSE 1016-2011/ASME A112.1016/CSA B125.16-11 standard that is specifically designed to provide thermal shock and scald protection at the flow rate of the showerhead and hand held shower being used. Ideally a plumbing professional should evaluate the entire hot water delivery and use system to determine whether additional protective controls are necessary to make the installation safer.
Finally, regulators, water providers and fellow efficiency advocates should refrain from establishing shower head and hand held shower flow rates and performance requirements outside of the ASME/CSA process. Instead, interested stakeholders are encouraged to participate in this process, and utilize the resultant shower head and hand held shower ASME/CSA criteria as a reference in green building and water efficiency guidelines.