It's a simple matter of physics: Moving water has the ability to transfer heat, either increasing or decreasing the temperature of the objects it contacts. This heat transfer, through moving water, has served to make mankind more comfortable and more productive through the years. Without it, motor vehicle transportation and many other "creature comforts," as well as 20th century life necessities like radiant heat would be impossible. The physical properties of heat transfer via water movement certainly can be beneficial. However, there are many instances when the temperatures that human beings are subjected to must be controlled within a high and low range to avoid injury. At the extremes of human exposure are hypothermia and scalding.
For many years, the operating water temperature range of industrial emergency drench showers and eyewashes was left open to fluctuations, based on ambient temperatures and other exposures. The water that flowed through emergency equipment was subject to climate, source and other variables that could raise it to dangerously high temperatures or lower it to hypothermia-inducing cold temperatures with no regulations or range limitations. You pulled the handle, pushed the flag or rotated the foot treadle on your emergency shower or eyewash and you got what you got. That is, until ANSI Z358.1-2004.
Municipally supplied water, when running for a sustained period, tends to cool down or heat up, eventually approaching its source point temperature. And, water subjected to hot or cold ambient temperatures in manufacturing plants or elsewhere can become dangerously hot or cold. The scenario perfectly depicts the effects of heat transfer.
What is "Suitable"?
Currently, OSHA standard 29CFR 1910.151 requires the availability of suitable first aid treatment facilities. Direction is given indicating that "suitable facilities for quick drenching or flushing of the eyes and body shall be provided ... " In the past, the definition of "suitable" generally was left to the specifier's discretion. However, ANSI Z358.1-2004 provides clarification that virtually eliminates all ambiguity. Sustained outlet temperatures, per the standard, must be no lower than 60 degrees F and below 100 degrees F during a full 15-minute use cycle for either an emergency shower or eyewash. Water that is colder could lead to hypothermia, while hotter temperatures can damage sensitive areas of the body, such as the eyes. Additionally, higher temperature water when applied to chemical splashes actually can intensify the injury. In either case, the discomfort of the victim also can lead to premature cessation of the emergency equipment use. The idea of an injured worker short-cutting the required emergency equipment use cycle because the water is too cold or hot has led to the notion of the "Comfort Zone" an outlet water temperature range that assures comfortable, non-injurious use of the equipment for the full 15-minute use cycle.
In this first part of this two-part series, we will discuss emergency equipment outlet water temperatures that exceed the 100-degree F maximum, thereby requiring cooling facilities. Consider, for example, an emergency drench shower/eyewash combination application in a petrochemical refinery in the Southwest. Radiant and ambient temperatures in many areas within a warm climate refinery often drive standing water temperatures above 120 degree F. The dynamics of heat transfer will raise the standing water temperature at the emergency equipment to dangerous levels approaching the maximum ambient/radiant temperature. When actuated, the emergency equipment would deliver very hot water to the injury victim, exacerbating the injury, creating more physical harm or causing the victim to recoil from the flow and cease the drench or irrigation protocol.
If you've ever washed your car on a hot summer day, you've probably witnessed a similar phenomenon. As you soap the car, the automatic sprayer on the hose is off, with a length of hose exposed to direct sunlight. When it's time to rinse off the soap, you grab the hose and squeeze the handle, immediately spraying out substantially warmer water than usual. The hot spray lasts until all of the water contained in the portion of the hose exposed to direct sunlight has been discharged. Now, consider what would happen if a large portion of the water supply immediately needed in an emergency was exposed to that much sustained heat and that water was fed into an eyewash or drench shower. It would make for a challenging and dangerous 15-minute drench or irrigation cycle! That's what the high side limit of the range established by ANSI Z358.1-2004 is designed to control.
With respect to cooling high ambient temperature water to bring it within the guidelines, the most popular approach is to size a chiller (see photo) and recirculation loop to maintain the proper temperature at all times for all equipment on the loop. A variety of different products are available, based on the volume of water required at peak demand and the footprint of the recirculation loop specified. As is also the case with warming technologies, all components must be matched to assure the availability of proper peak flow rates and temperatures. Emergency equipment manufacturers are in the best position to assist with system design, as they know their equipment flow rates, peak demands and other associated requirements.
Just as progress has given us full function emergency equipment and, later on, tepid water requirements, it now has given us a clearly defined minimum and maximum range of acceptable outlet temperatures. Designing and managing an emergency equipment system that is capable of delivering sustained use volumes of properly tempered water should be a step-by-step process. It's a matter of identifying your risks, sizing your total system for peak flow use and factoring in local water conditions (pressure and temperature), as well as seasonal and process-related variations. Only then is it possible to specify and match your overall need to a tailored system, capable of delivering emergency equipment water temperatures that are just right!
Next month we will consider the methods and technologies available to warm input water supplies that are below the ANSI-mandated 60 degrees F.
For more information on the tempering systems, visit www.hawsco.com/pe.
Casey Hayes is the engineering manager at Haws Corp., located in Sparks, Nev. He can be reached at (775) 353-8320 or [email protected] Haws Corp. designs, manufactures and distributes drinking fountains and emergency equipment that are ranked No. 1 in quality by specifiers in both product categories.