Water Supply
Proper operation of emergency equipment requires the availability of a large and continuous supply of potable water. The water supply must, at a minimum, be capable of delivering the volumes of water required by the ANSI standard. Piping should be at least as large as the inlet size of the unit to be installed. The water supply line must also be capable of delivering an uninterruptible flow of water of at least 30 PSI flow pressure.
Water Temperature
The ANSI standard provides that the water delivered by emergency equipment be “tepid” (that is, moderately warm or lukewarm). Tepid water is generally defined as between 60 and 100 degrees Fahrenheit. However, where it is possible that a chemical reaction might be accelerated by warm water, a medical professional should be consulted to determine what the optimum water temperature would be.
The delivery of tepid water to emergency equipment may raise complicated engineering issues. In geographical areas subject to cold weather, the water supplied by public water systems can be quite cold, at times just above freezing. Providing tepid water requires heating the cold water or blending it with hot water to achieve a desirable temperature. Conversely, in warm areas of the country, water standing in pipelines can be heated to a very hot temperature. Providing tempered water would then involve chilling the water or adding cold water to the water supply line.
There are several ways to design a water supply system to address the tepid water requirement. First, it is possible to provide both hot and cold water supply lines to each location at which emergency equipment is installed. This is typically done in facilities (such as laboratory buildings and schools) where hot and cold water systems are installed throughout the building. At each emergency unit, a tempering valve would be installed to blend the hot and cold water to a preset temperature. The tempering valve must be specially designed for use with emergency equipment, since these valves have dual built-in safety features. In the event that there is an interruption in the hot water supply, the valve will still deliver a full flow of cold water to the equipment. If there is an interruption in the cold water supply, the valve will shut off the water entirely to eliminate the possibility of scalding. Please refer to the “Tempering Units” section of this catalog for information on Guardian tempering valves.
The second way to address the tepid water issue is to install a recirculating tepid water system. This system can supply multiple emergency equipment stations. The system continually recirculates warm water to each location. If one or more units are activated, the system will automatically blend hot and cold water and add it to the water line to supply the units. These systems must be sized and engineered for the particular facility in which they are to be installed. It is therefore common to consult with the emergency equipment manufacturer during the design process. Please contact our regional sales representatives or the factory for information on recirculating tempered water systems.
One of the things to note in what pennpiper quoted is the references to the ANSI standard. Although the number isn't given, the repeated references means there is one and it behoves you to find it if you're designing a safety shower.
Patricia Lougheed
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Forget about ANSI. The article references an obsolete standard ANSI 117.1 that pertained to handicapped access. The other standard was ANSI Z358.1 for emergency eyewas and shower equipment. This too is inactive and withdrawn. However the current standard is the Industrial Safety Equipment Association standard ISEA Z358.1 2004.
The ISEA web site indicates that ISEA received ANSI approval for a revised edition of the standard for Emergency Eyewash and Shower Equipment, ANSI / ISEA Z358.1-2004.
Plumbed units tend to flow more than these minumums at a design residual of 30 PSI, and varies significantly by manufacturer--some have flow controls and others have what amounts to an uncontrolled open-pipe flow.
ANSI isn't clear on what they mean by an inlet supply (i.e. static? residual?) pressure of 0.207 MPA/30 PSI "but has been chosen because meeting the installation requirements may place units at unusual distances from and elevations above normal supply lines. In such cases, it is the responsibility of the designer and owner to ensure proper flushing fluid delivery at possible low points of pressure in the plumbing system." [Appendix B.2, ANSI Z358.1-2004]
On that note, I have an editorial comment: They obviously didn't consult any plumbing engineers with regard to establishing a clear and sensible pressure requirement--which in this case, an interpreted 30 psi residual, is unnecessarilly large and results in also unnecessarilly large cost implications to plumbing systems.
Is there a minimum amount of time that these flowrates have to be maintained for?
I remember doing a skidded safety shower, and 15 minutes of continuous flow was a requirement - 20 GPM for 15 minutes = 300 gallons. Don't quote me on the exact numbers, but I am pretty sure I recall a required length of time.
Please comment?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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You are correct. The ANSI standard prescribes a minimum 15 minute duration for delivery of flushing fluid. Getting an accurate design flow is obviously important for estimating the hot water requirements for these, as they tend to be quite large. It's also rather pointless to design a hot water capacity to the ANSI minimums if the actual device installed doesn't have any flow control--ANSI doesn't limit the maximum flow.
Here's a good reference for the current standard, which covers all aspects of the equipment, access, signs & lighting, critical dimensions, etc.:
ANSI Requirements for Emergency Fixtures - 2004
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Please do not rely on standards alone. They only prescribe a minimum legal requirement. When we consider peoples wellbeing, we have a duty of care to assess the situation more thoroughly. For example, in the Alumina Refining industry, the main hazard is exposure to hot caustic solution. We have it driven into our heads that after exposure, we have to shower under cold water for a minimum of 20 minutes (this can be fun in some of the colder climate winters of the southern Australian refineries!!!). Not removing all of the caustic can result in some very horrific burns. So please consider the application, likely exposures for which the safety shower is installed and get advise from the Material Safety Data Sheets or a resident OSH expert.
Thanks
a) I do not think that OSHA has yet referenced the latest ANSI spec which rerquires "tepid" water.
b) Every site I worked at that is below teh mason-Dixon line has avoided using tepid water in the emergency showers. The only site I personnaly know has installed the tepid shower was in New England.
c) the state of north carolina plumbing code has defined tepid water as cold water when the term is applied to safety showers.
d)Conventional safety showers that require hot water imply a huge cost adder when the shower is located at a remote location that might not had otherwise been provided with a building or electrical power. A possible lower cost alternative would be to store the 15 minutes worth of hot water in a container that also has a eutectic salt heat exchanger- a small 100 W heater can be used to continuously maintain the salt at 95 F, and when the shower has to be operated, the salt change of phase will act as the surge heater for the water surge.
