Safety showers and eyewash stations are installed when dangerous goods are present. The shower installation has to meet recognised standards like American National Standard Z385.1. This article notes the key requirements for safety shower installations and discusses some practical issues.
The distance to a shower from the place of work is often stipulated in relevant design codes. Examples are codes for dangerous goods storage and transport and laboratory construction. For bulk dangerous goods applications a maximum distance is typically 7 meters, in a laboratory 30 meters. No obstructions are allowed in the way to the shower. It would not be acceptable to expect a person in an emergency to navigate a set of stairs to get to a shower.
Determination of the place of work can be a difficult question. In a laboratory the position of the benches and areas of chemical storage are clearly identifiable. However in a dangerous goods storage facility the place of work can be at numerous locations. The easily identifiable locations will be where operators usually work or where maintainers have to go and repair equipment. Each of these positions would need a safety shower. For those occasions where work has to be done away from a safety shower it is necessary to use a portable shower with 25-mm (1”) hoses connecting it to the potable (drinkable) water supply.
A safety shower must be identified with an appropriate sign and be well lighted. The sign typically is 300 mm wide by 400 mm long with the words “Safety Shower” and a symbol of a shower in white on a green background. Many facilities install a separate green light above the shower to meet the requirements of sufficient lighting and to signpost the shower’s location.
The shower and eyewash must be designed to provide sufficient flow and pressure of water. When the shower is turned on there must be a minimum deluge flow of 76 lt/min. The water must flow non-stop at the minimum flow rate and pressure for at least 15 minutes. In addition the spray pattern must provide adequate coverage. In Z358.1 the specification is a 508-mm (20”) diameter spray cone at 1524-mm (60”) above the surface the user stands on.
Shower dimensions such as height and depth, the position of handles, tap arm and foot pedal positions and the location of any eye wash basin are all specified to meet ergonomic considerations and the range of sizes of people.
Only drinkable quality water can be used for safety showers. Local regulations may require the installation of a back flow prevention device (reduced pressure zone device) at the mains water supply point to insure no contaminants can be sucked back into the potable water supply. Check with the local water authority for their requirements.
The safety shower supply piping must be dedicated only to the purpose of delivering water to showers and eyewashes. Nothing else is to be supplied from the safety shower piping circuit. Taps are not to be installed on showers for hose down purposes. If during emergencies water pressure was low because safety shower water was being used for hose down water elsewhere it may result in the person under the shower getting much more severely hurt than was necessary.
The minimum diameter piping to a safety shower is 25 mm. The materials used in the piping system must not rust or contaminate the water and must not be degraded by the environment. Plastic piping used above ground to safety showers needs protection from damage and sunlight. The system must be designed for pressure losses through the pipe work so that minimum pressure and flow are available at any shower when put on.
This introduces the dilemma of deciding how many showers need to be supplied at the same time. Determination of the answer requires review of:
• the frequency of work occurring in the facility,
• the number of locations where people will be exposed to danger at the same time,
• the likelihood that more than one person will be splashed by chemicals in the one incident,
• the likelihood of multiple incidences at the same time,
• the availability of sufficient water pressure and flow for a sufficient period of time.
A minimum of two in use at a time should be assumed.
A good practice is to run the supply pipe work as a ring-main so that water can come from two directions. This provides maximum water flow to all showers. Keep the take-off piping from the ring-main to individual showers as short as possible to maximise water flow and pressure at the shower. If the supply pressure is excessive it must be reduced through a pressure reduction valve.
If the supply pressure is low an in-line booster pump is installed at the supply point. The booster pump operates under the control of a pressure switch that detects a fall in pressure when a shower is put on and turns on the pump to boost pressure and flow to that required at the shower.
The water temperature from the safety shower must be comfortable for the human body. Typically the range is 15 – 35o C. Water in pipes exposed to the sun will get hot. Good practice is to bury the piping at least 600 mm (2’) underground where the temperature does not fluctuate greatly throughout the year. When burying pipes follow good excavation practices that keep the pipe in a safe, reliable condition.
Maintenance and Inspection
Recommend practice is to operate the shower weekly to prove it is working and available for use. Linkages can stiffen from the ingress of dirt or they have been incorrectly set up and do not work properly. Every twelve (12) months it is necessary to confirm the shower still meets minimum plumbing, flow and pressure requirements. Keep records of the inspection and fix problems immediately.
Showers mounted on steel structures with vibrations traveling through the mounting platform can turn themselves on. The situation is more likely if the shower is on an outside vibrating platform in the wind. Water dripping from showers and eyewashes is a common occurrence. In both cases it is necessary to tighten the linkages to remove looseness. Dripping water, failed lighting, poor signage and disconnected foot pedals are housekeeping issues to be reported to the maintenance department for rectification.
Mike Sondalini – Maintenance Engineer
We (Accendo Reliability) published this article with the kind permission of Feed Forward Publishing, a subsidiary of BIN95.com
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