Sulphuric Acid Plant Safety - Safety Showers
March 28, 2003

Introduction Safety Showers         Performance of Control Valve         Installation         Testing Eyewash Units         Performance of Control Valve         Installation         Testing Dunk Tank Tempering Tanks for Emergency Showers and Eyewashes         Tempered Water Requirements         Tempering Methods         Tank Installation

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Introduction

Safety showers and eyewashes are an important piece of safety equipment in an acid plant.  Proper design, location and installation will ensure that they are available in an emergency.

Safety Showers

Emergency shower heads shall be designed so that a water column is produced that is not less than 208.3 cm (82 inches) nor more than 243.8 cm (96 inches) in height from the surface on which the user stands.  The spray pattern shall have a minimum diameter of 50.8 cm (20 inches) at 152.4 cm (60 inches) above the surface on which the user stands, and the centre of the spray pattern shall be located at least 40.6 cm (16 inches) from any obstruction.   Emergency shower heads should be capable of delivering a minimum of 113.6 L/min (30 USGPM) of water, which shall be substantially dispersed throughout the pattern.

In combination units, the eyewash is not considered an obstruction for the purpose of determining the distance of the centre of the spray pattern.

Shower head designers usually use 113.6 L/min (30 USGPM) at 207 kPa (30 psi).

Performance of Control Valve

The valve shall be designed so that the water flow remains on without requiring the use of the operator’s hands.  The valve shall be designed to remain activated until intentionally shut off.   The valve shall be simple to operate and shall go from ‘off’ to ‘on’ in one second or less.  The valve shall be resistant to corrosion from potable water.

Manual actuators should be located not more than 175.3 cm (69 inches) above the surface on which the user stands.

Installation

Emergency showers shall be in accessible locations that require no more than 10 seconds to reach and should be within a travel distance no greater than 30.5 m (100 ft) from the hazard.

The unit should be located as close to the hazard as possible without physically causing a hazard itself, such as protruding fittings.  The maximum time required to reach the shower should be determined by the potential effect of the chemical.  For example, exposure to a highly corrosive chemical might require showers to be installed within 3 to 6 m (10 to 20 ft) from the hazard.

Each emergency shower location shall be identified with a highly visible sign.  The area around or behind the emergency shower, or both shall be painted a bright colour and shall be well lighted.

Testing

Showers shall be activated weekly to flush the line and to verify proper operation.

The shower shall be tested in accordance with the following procedures:

• With the unit correctly connected to the water source and the valve(s) closed, visually check the piping connections for leaks.

• Open the valve to the full open position.  The valve shall remain open without further use of the operator’s hands.

• Measure the shower.  The face of the shower head shall not be less than 208.3 cm (82 inches) nor more than 243.8 cm (96 inches) from the surface on which the user stands.

• With the valve in the ‘full on’ position, measure the diameter of the spray pattern.   It shall be a minimum of 50.8 cm (20 inches) at 152.5 cm (60 inches) above the standing surface.  The centre of the spray shall be at least 40.6 cm (16 inches) from any obstructions.

Eyewash Units

A means shall be provided to ensure that a controlled flow of potable water or its equivalent is provided to both eyes simultaneously at a velocity low enough not to be injurious to the user.

There shall be no sharp projections anywhere in the operating area of the unit.

Nozzles shall be protected from airborne contaminants.  Whatever means is used to afford such protection , its removal shall not require a separate motion by the operator when activating the unit.

Eyewash equipment shall be capable of delivering to the eyes not less than 1.5 L.min (0.4 USGPM) for 15 minutes.

Eye/face wash equipment shall be capable of delivering to the eyes and face not less than 11.4 L.min (3.0 USGPM) for 15 minutes.

The unit shall be designed to provide enough room to allow the eyelids to be held open with the hands while the eyes are in the stream of water.

Performance of Control Valve

The valve shall be designed so that the water flow remains on without requiring the use of the operator’s hands.  The valve shall be designed to remain activated until intentionally shut off.  The valve shall be simple to operate and shall go from ‘off’ to ‘on’ in one second or less.  The valve shall be resistant to corrosion from potable water.   The valve actuator shall be large enough to be easily located and operated by the user.

Installation

The unit shall be positioned with the water nozzles 83.8 cm (33 inches) to 114.3 cm (45 inches) from the floor.

Eyewash units shall be in accessible locations that require no more than 10 seconds to reach and should be within a travel distance no greater than 30.5 m (100 ft) from the hazard.

The unit should be located as close to the hazard as possible without physically causing a hazard itself, such as protruding fittings.  The maximum time required to reach the shower should be determined by the potential effect of the chemical.  For example, exposure to a highly corrosive chemical might require showers to be installed within 3 to 6 m (10 to 20 ft) from the hazard.

Each eyewash location shall be identified with a highly visible sign.  The area around or behind the emergency shower, or both shall be painted a bright colour and shall be well lighted.

Testing

Eyewashes shall be activated weekly to flush the line and to verify proper operation.

The eyewash shall be tested in accordance with the following procedures:

• With the unit correctly connected to the water source and the valve(s) closed, visually check the piping connections for leaks.

• Open the valve to the full open position.  The valve shall remain open without further use of the operator’s hands.

• Using a flowmeter or other means, determine that the flow rate is at least 1.5 L/min (0.4 USGPM), that the flushing streams rise to approximately equal heights, and that the water will wash both eyes simultaneously at a velocity low enough not to be injurious to the user.

• To determine that both streams are properly located for flushing simultaneously, a strip of transparent material 10.16 cm (4 inches) wide marked with two sets of parallel lines equidistant from the centre, on set 3.18 cm (1 1/4 inches) apart and the other 8.26 cm (3 1/4 inches) apart.  Place this strip on top of the stream of the eyewash;  the flushing should cover the areas between the lines 3.18 cm apart and the lines 8.26 cm apart when the gauge is lowered not more than 3.81 cm (1 1/2 inches) below the water’s peak.

Dunk Tanks

Dunk tanks are essentially large bath tube in which a person can be completely immersed.  The tanks are really only suitable for indoor use where the building is heated.  Installation outdoors can result in the water temperature being too low and in cold climates the water may freeze.  A continuous flow of water into the tank is generally required to ensure the tank is full and to keep the water fresh.

 

Tempering Tanks for Emergency Showers and Eyewashes

A tempering tank may be described as “a pressure vessel used exclusively for hydraulic purposes at atmospheric temperature”.  Tempering of water for safety showers and eye/face washes should be done by conduction of heat from adjacent air space to the tank and its contents, i.e. within water temperature limits of 16ºC and 40ºC (60ºF and 110ºF).   Tempering methods employing direct steam or electrical energy, e.g. steam mixing systems ort immersion heaters, etc. are NOT recommended for use with emergency showers.   The most suitable and economical choice of tank for tempered water service is a standard hot water storage tank (100 psi working pressure, hot dip galvanized internally and externally). 

Tempered Water Requirements

The function of the tempering tank is to provide a supply of water, between tolerable temperature limits, for use at the shower head or eye/face wash.  It is not intended as a reservoir to provide water when the supply to the tank is shut off.  The recommended water supply to emergency showers is as follows:

Temperature:	16ºC (60ºF) Minimum 40ºC (110ºF) Maximum
Flow:	30 USGPM
Line Pressure:	60 psi Maximum

The tempering tank should have a capacity of not less than 170 Imp. gallons.  Where there is more than one emergency shower in a building, one tempering tank may be used to supply all showers (provided connecting piping does not run through areas heated to less than 16ºC) since the possibility of more than one unit being required simultaneously would be slight.

Tempering Methods

Since the tempering tank is to supply an emergency shower and eyewash the tempering tank must not introduce an additional hazard.   Direct heating methods require temperature controls and if these fail, the result could be excessively hot or cold water delivered to the shower head and therefore should not be used.  The following methods avoid the direct application of heat and should be used:

• Uninsulated tank located in a heated area where the contents will remain at an ambient temperature of 16ºC to 40ºC.

• Uninsulated tank located in an unheated area but enclosed and the enclosed space heated by steam, hot water or electric radiant heater with the temperature limits stated above.

Tank Installation

• Since the tempered water is intended to be at ambient temperature, the tank should not be insulated.

• Tank orientation should be such that inspection openings (where applicable) are easily accessible.

• The tank should be installed vertically wherever possible.

• The main valve in the supply line to the tank should be sealled open and tagged to indicate that a temporary connection must be made to the tank before the main valve is closed.

• When the tank is isolated for inspection or repair, a temporary connection should be made between supply and discharge connections or an alternate safety shower or eye/face wash station should be made available.

• Provision should be made to remove entrapped air from the system, particularly during initial and subsequent tank filling operations.  An automatic air vent should be installed near the highest point in the system.

• The emergency showers and eye/face wash location require careful consideration, so that they are neither too far from or too close to the hazard and that no obstructions are in the path leading to the emergency shower or eye/face wash.

• Outside potable water supply lines serving tempering tanks should be run underground below frost level to avoid problems of overheating or freezing due to failure of the tracing system required for above ground lines.