e10k

Corporate Engineering Standard Engineering Standard: E10K

Electrical Technology Network

E10K Electrical Trace Heating for Freeze Protection

of Safety Showers Table of Contents

1. User guidance ....................................................................................................................................................2 1.1 Scope .........................................................................................................................................................2 1.2 Applicability ................................................................................................................................................2 1.3 Benefits ......................................................................................................................................................2 1.4 Definitions...................................................................................................................................................2 1.5 References .................................................................................................................................................2

2. General ................................................................................................................................................................3 3. Design .................................................................................................................................................................3

3.1 Pre-fabricated.............................................................................................................................................3 3.2 Field-Built....................................................................................................................................................3

4. Temperature control ..........................................................................................................................................4 4.1 Pre-Fabricated............................................................................................................................................4 4.2 Field Built....................................................................................................................................................4 4.3 Excessive Water Temperature Protection..................................................................................................4

5. Monitoring & Alarms Considerations ..............................................................................................................5 5.1 Pre-fabricated and Field-built units ............................................................................................................5

6. Installation of field built safety shower units. .................................................................................................6 List of Figures Figure 1. Typical heating pre-fabricated safety shower.............................................................................................7 List of Tables Table 1. Typical heat loss & heating cable for safety showers ...............................................................................4 Red text indicates revisions made in the February 2008 issue.

Vendors and merchandise designations are given to describe materials and may not include all acceptable products. Substitutions by suppliers are to be made only on approval of the local authority initiating the use of this standard.

Document revised February 2008 / Entire document reaffirmed February 2008 Contact [email protected] by e-mail for more information. This document may be used and reproduced for DuPont business only.

Copyright 2001, 2005, 2008 E.I. du Pont de Nemours and Company. All Rights Reserved. (Unpublished)(Engineering) Page 1 of 7

E10K Electrical Trace Heating for Freeze Protection of Safety Showers

1. User guidance

1.1 Scope

This standard provides details and information for the selection of electrical traced, pre-fabricated safety shower units, and for the installation of electrical heat tracing on field-fabricated safety showers as described in DuPont Corporate Safety Standard S1E which are subject to freezing in outdoor or unheated indoor areas.

This standard generally does not apply to Tempered Water Systems as described in S1E. Due to the potential for scalding and high cost, Tempered Water Systems require the combined support of SHE, process/power function and electrical heating specialists to manage the need, regulatory requirements, safety issues that may include bacteria growth, thermal burn, solar gain, and temperature uniformity. System design, hazard analysis, equipment selection, safety devices/controls, temperature control, system monitoring and alarms are inclusive considerations for these systems.

1.2 Applicability

The DuPont sites worldwide that follow the requirements of the U.S. National Electrical Code should follow this standard.

1.3 Benefits

Using this standard will:

Provide a basis for freeze protecting emergency safety shower eyewash units in alignment with the NEC (NFPA 70) and DuPont Standard S1E.

Establish a minimum essential design threshold. Facilitate selection of pre-fabricated safety showers. 1.4 Definitions

Runaway Pipe Temperature: The highest equilibrium pipe temperature that occurs when the heating cable is continuously energized at the maximum ambient temperature.

1.5 References Links to the following standards can be accessed from this section.

DE1H Design & Application of Electrical Resistance Heat Tracing for Pipelines

E7K Electrical Pipeline Heat Tracing -Installation Details

E16L Safety Shower Indicating Light

S1E Safety Shower & Eyewash Facilities

SE32.3B Electric heat Tracing, Cables and Panels

SE40.4B Thermostats for Pipeline and Vessel Heating Circuits

NFPA 70 (National Electrical Code, NEC)

National Fire Protection AssociationSpecific articles of the NEC are referenced throughout the text.

Document revised February 2008 / Entire document reaffirmed February 2008 Copyright 2001, 2005, 2008 E.I. du Pont de Nemours and Company. All Rights Reserved. Used under Copyright License. Page 2 of 7


2. General The basic requirements for Safety Shower and Eyewash installations are covered in S1E. Based on cost of installation and operation, electric heat tracing has become the first choice for protecting safety shower units from freezing, replacing past popular use of low-pressure steam for this purpose.

Safety shower units can be field-built or purchased as pre-fabricated units. Pre-fabricated units are widely used and available from both emergency equipment suppliers and electric heating manufacturers that are listed by the manufacturer for both non-classified and hazardous areas. Pre-Fabricated units often include a wide selection of optional features such as location light, power monitoring lights, flow alarms, mechanical anti-scald & freeze prevention valves, and more. Field built units commonly have minimum essential features and require the user to incorporate devices that are listed for the intended use in a manner that meets installation codes and standards.

3. Design Safety shower freeze protection is somewhat different that freeze protection of water pipes. Section C in S1E limits water temperature to a maximum of 38C (100F), S1E recommends the maximum water temperature of 25C (77F) to reduce the potential for bacterial growth and a minimum water temperature of 16C (60F).

In order to balance the prevention of freezing from the possibility of excessive water temperatures, the design basis for safety showers commonly selects a safety factor of 10% for heat-loss calculations as opposed to higher safety factors applied to process or other freeze protection applications. Typical calculated heat loss values for 1 & 1.5 thick polyisocyanurate insulation are indicated in Table 1.

Ground-fault protection is required by the NEC and IEC for electric heat tracing circuits. The required protection can be provided by a dedicated ground-fault circuit breaker (typically a 30ma trip equipment protection device) or an electronic heating controller with integral (fixed or adjustable) ground-fault protection.

3.1 Pre-fabricated

Verify the manufacturers design basis for operation at the site by considering the minimum ambient temperature along with calculated runaway pipe temperature based on site conditions. Note: The application of optional mechanical anti-freeze valves that cause water to flow in freezing temperatures may eliminate the need for electric tracing in geographical areas that only experience freezing temperatures of short duration in a 5 to 10 year climatic event.

3.2 Field-Built

Low-temperature self-regulating heat tracing cable shall be selected per SE32.3B - Section 5.1. These cables provide the minimum heat to keep the water temperature in the shower to 16C (60F) at the designated site minimum ambient temperature, with a 32 kilometer per hour (20 mph wind), and a 10% safety factor in heat-loss calculations.



Table 1. Typical heat loss & heating cable for safety showers

Minimum Ambient design Temp. C (F) -12C (10F) -17.7C (0F) -23C (-10F) -28C (-20F) Differential Temperature to maintain 15.5C (60F) 27.5

oC (50oF) 33oC (60oF) 38.5oC (70oF) 43.5oC (80oF)

Watts/linear meter (foot) 1 polyisocyanurate Insulation 7.2 (2.2) 8.5 (2.6) 10 (3.1) 11.5 (3.5)

Watts/linear meter (foot) 1.5 polyisocyanurate Insulation 5.6 (1.7) 6.5 (2.0) 7.9 (2.4) 8.8 (2.7)

Note: Based on 1-1/2 galvanized steel pipe, Rigid Polyisocyanurate Thermal Insulation, 10% Safety Factor. Output of typical heating self-regulating heating cables (Thermon BSX or Tyco Thermal BTV family) at 60F is 8.5 W/m (2.6 W/ft) for a 10 W/m (3 W/ft) cable and 14.8 W/m (4.5 W/ft) for a 16 W/m (5 W/ft) cable.

4. Temperature control Temperature control considerations for safety showers include fixed temperature immersion, pipe sensing and ambient sensing depending on fabrication method and risk of excessive water temperature.

4.1 Pre-Fabricated

Pre-fabricated safety shower/eyewash units as supplied by emergency equipment manufacturers are normally supplied with fixed-temperature, immersion type thermostats that sense water temperature. Pre-fabricated safety shower/eyewash units supplied by electric heating equipment manufacturers commonly use fixed-temperature pipe sensing thermostats. Either of these methods meets the needs of basic temperature control but the immersion thermostats are difficult to test for operation. A second layer of temperature protection may be required to prevent excessive water temperature as described in section 4.3.

Pre-fabricated units are commonly available with optional mechanical-type scald and/or freeze valves that activate in freezing temperatures and allow sufficient water to flow to prevent freezing. The optional freeze valves may be justified where power may be lost in freezing weather, or as a measure of protection to prevent excessive water temperature, see section 4.3.

4.2 Field Built

Field built units should use either a pipe-sensing electro-mechanical thermostat or electronic controller set at 16C (60F). The sensing bulb should be taped to the pipe in an area that will remain full of water and self-adhesive aluminum heat-transfer tape should be used to secure the sensing bulb (or RTD) to the pipe. A second layer of temperature protection may be required to prevent excessive water temperature as described in section 4.3.

4.3 Excessive Water Temperature Protection

A potential high water temperature hazard exists if the temperature control device fails in a manner where power is continuously supplied to the heat tracing. As the ambient temperature rises above 16C (60F) the water temperature can reach a temperature in excessive of the stated limit of 37.7C (100F). Both 10 W/m (3 W/ft) and 16 W/m (5 w/ft) heating cables will result in the same condition but the ambient crossover temperature will vary. In most cases a failure of the temperature control device in safety shower applications can go undetected for long periods of time.



S1E, section 5.5.1 defines testing frequency for safety showers that vary from daily to weekly depending on shower location and hazard exposure. Safety showers that are tested daily or tested each time before work is performed with a minimum 30 second flush time should provide for protection from excessive water temperature without the need for extra layers of protection.

If safety showers are not tested daily or before each activity as described above a second layer of protection shall be provided. The second layer of protection can include (but is not limited to) the following:

A single heating-controller that includes a high-temperature alarm that is wired to a manned location (process control system) and must be acknowledged before reset.

A second pipe for sensing water temperature which functions as a high-limit temperature control device. If this option is used consider an electronic controller with a digital temperature display, local alarm or other method to provide an alert that the primary temperature control has failed.

Use an ambient sensing electronic controller to control a group of safety shower with a high-temperature limit in each unit. Pre-fabricated safety showers can often be ordered with a high-limit in place of the standard temperature at no extra cost for units with fixed-temperature immersion thermostats. Other pre-fabricated units using a pipe sensing thermostat can change the temperature set-point to act as a high-limit.

Purchase pre-fabricated units with a mechanical temperature-actuated (scald) valve. Note: Discuss performance of valves with manufacturer with respect to leaking in-service.

5. Monitoring & Alarms Considerations Monitoring requirements for safety shower and eyewash units range from simple monitoring for presence of voltage to the heating circuit, to a signal that emergency flushing is in progress.

5.1 Pre-fabricated and Field-built units

The minimum essential method within DuPont for monitoring the heat tracing power is to power the Green Safety Shower Indicating Light that is commonly provided at each shower (E16L) to the same circuit as the heat tracing. In this case if the green light is not operating it is expected that personnel will investigate the trouble to determine if the problem is the light bulb failure or loss of circuit power.

Another monitoring method, that may be especially useful at remote locations, is to connect a heating manufacturers standard end-of-line monitoring light into the heat-trace circuit. In this case it is expected that operating personnel would check the light as part of testing the unit for operation before engaging in work and/or cold-weather patrols would check the light. Unless there are administrative controls establishing procedures for monitoring the light it is often an unnecessary cost.

Alarms that signal that emergency flushing is in progress shall be provided on safety shower and eyewash units located in rigid enclosures and are particularly important in remote, high-hazard areas or operating units with low occupancy rates. Alarms of this type are used to initiate emergency response measures. Safety shower in-use alarms are commonly initiated by non-contact (proximity-type) valve-position switches. Paddle-type flow-switches may also be used as long as they activate on the low flow associated with eyewash units.



When safety shower availability is required for process operation, as in some highly-hazardous processes, a heating circuit loss-of-voltage condition should be signaled to the process control system.

6. Installation of field built safety shower units. Select the heating cable based on site conditions per section 3. Install the heating cable on the pipe using the recommended heat tracing installation details (E7K) using installers trained by the manufacturer. Provide required extra heating cable at fittings, pipe supports or other heat-sinks. Note: self-regulating heating cable may be overlapped as required. Fasten cable to pipe and fittings using glass cloth tape from the heating manufacturer. Install thermal insulation to cover the entire heated section of the assembly. Use self-adhesive aluminum heat transfer tape for heating supplier to secure temperature sensors to pipe.

Where the water is supplied from underground pipelines the tracing should extend 0.6 m (2 ft) below the ground-level inside the thermal insulation.



Figure 1. Typical heating pre-fabricated safety shower

Front elevation Side elevation

Note: Tyco Thermal Controls, one of the DuPont Companys heat-tracing Strategic Alliance Agreement Suppliers, offers a pre-traced safety shower (shower guard) with multiple equipment options.


1. User guidance1.1 Scope1.2 Applicability1.3 Benefits1.4 Definitions1.5 References Links to the following standards can be accessed from this section.2. General3. Design3.1 Pre-fabricated3.2 Field-BuiltTable 1. Typical heat loss & heating cable for safety showers 4. Temperature control4.1 Pre-Fabricated4.2 Field Built4.3 Excessive Water Temperature Protection5. Monitoring & Alarms Considerations5.1 Pre-fabricated and Field-built units6. Installation of field built safety shower units.Figure 1. Typical heating pre-fabricated safety shower

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