Patol Limited

Patol Digital Linear Heat Detecting Cable (LHDC) may be employed for the detection of fire conditions related to various risks on petro-chemical storage sites. The LHDC system has a proven record of being an indispensable aspect of the protection regimes that prevent catastrophic events as shown in the above photograph.

Digital LHDC is unique in that it can be readily installed in close proximity to risks where flammable gases may ignite and will tolerate these arduous chemical and environmental rigors as a normal condition.

Rapid  detection of anomalies permits early application of containment measures such as foam extinguishing.

Some of the prime features of the system are as follows:-

¨ Floating Roof Tank Rim Seal protection - Including Retractable Cables

 

¨ Fixed Roof Tank protection - Vents, Gauging Points, Inspection Covers.

 

¨ Monitoring of Pipes, Manifold Systems and Product Pumps .

 

¨ Alarm and Process Control Interfaces - Distance / Location Metering .

 

¨ Intrinsically Safe operation using certified Barriers / Isolators.

 

¨ UL Listed.

PATOL LINEAR HEAT DETECTING CABLE

LHDC FIRE SYSTEM PRODUCT GUIDE

PETRO-CHEMICAL BULK STORAGE FACILITY

TEMPERATURE

REACTIVE

POLYMER

INSULATION

Fig.1

The protection of storage tanks with floating roofs requires special consideration of the monitoring of the ‘Rim Seal’ between the floating roof (pontoon) and the tank wall.

Various mechanisms are employed as the primary seal which include:- Mechanical Shoe, Scissor, Liquid Mount Foam & Vapour Mount.

Often a secondary (or weather) seal is located above the primary seal. The photograph to the left shows the external (top) view of such a compression plate secondary seal.

This design provides an integral extinguishing foam ‘gutter’. Other configurations employ a ‘Foam Dam’ welded to the pontoon edge.

The LHDC is mounted above the rim seal at a location where it will most readily detect any leaked vapour ignition that may occur.

Figure 2 shows a typical arrangement where the LHDC monitors a secondary seal of similar nature to that of the above photograph.

In this case the mounting brackets are fixed to the edge of the roof  pontoon and extend out to cover the secondary seal’s ‘motion point’ with the tank’s shell wall.

Various mechanisms are available for fixing the LHDC to brackets. See standard fixings for examples.

Figure 3 shows an installation arrangement where the LHDC is mounted via brackets to the shoe of a primary “scissors / pantograph’ seal.

There is a considerable variety of mechanical arrangements of rim seals. Each must be separately examined and the most practical mounting method determined.

In many cases fixings from Patol’s standard range may be utilised.

Some rim seal arrangements will require ‘special’ brackets to correctly locate the LHDC. Patol can both design and fabricate mountings on provision of rim seal mechanical data.

Petro-chemical Product Pumps

LHDC Terminator / EOL

Junction Box

Two Core Fire Proof Cable

To Safe Area

Patol Digital LHDC

Fig.8

Motor

Detector Cable Support Framework

Pump

Faults related to petro-chemical product pumps can in many cases cause a fire. Generally the failure of the pump motor or coupling causes a seal failure resulting in product leakage together with its associated fire potential.

The LHDC is secured to a support framework which is mounted directly above the pump bearing / seal area. This arrangement provides good coverage and early detection whilst  giving sufficient clearance to enable easy access for pump maintenance work.

A number of pumps may be monitored as a single zone as shown in figure 8 above.

Fig.9

SAFE AREA

HAZARDOUS AREA

Patol can provide versatile interface equipment specifically designed to monitor LHDC located in hazardous areas. The use of Intrinsically Safe Barriers is integral to the design in order to ensure correct operation and optimise the amount of LHDC permissible within the hazardous area.

The system incorporates many features that facilitate compatible connection to site Alarm & Control Schemes such as multiple ‘volt free’ contacts for both Alarm and Fault. An LCD ‘Alarm Point Locator’ display provides the distance to initiating point which is invaluable during both event and maintenance.

The LHDC can also be configured to directly connect to ‘industry standard’ fire alarm system trigger circuits and addressable loop auxiliary switch monitoring modules. Care must be taken in the implementation of IS barriers to ensure operational compatibility. The permissible lengths of installed LHDC may be limited. See IS Barriers section below.

Three typical cable & monitoring arrangements are shown in figure 9.

 

 

Fig.4

Fig.5

Fig.6

Fig.7

Stainless Steel

Collecting Cone

Part No. 700-553

Part No. 700-551

Core Quantity            4 off

Core Size                  14/0.15mm (0.25mm²)

Inner Screen              64/0.1mm TCW - 95%

Sheath Material         Nylon

Diameter                   7mm

Extended Length       24m

Part No. 700-552

Core Quantity            4 off

Core Size                  16/0.2mm (0.5mm²)

Sheath Material         Nylon

Diameter                   7mm

Extended Length       29m

The retractable cable is connected between two junction boxes. One is located on the tank shell rim, the other on the floating roof. Either of the junction boxes can be employed to house the EOL device.

A collecting cone is used to gather the 2.2m retracted coil of Part No. 700-551.

Part No. 700-552 has a much shorter retracted length and does not require the collector.

 

LDM-519-DDL Interface

The module has LED indication of Fire, Fault and Supply status.

The unit also has a 3½ digit LCD which activates on fire condition and displays the distance into the zone that the alarm has occurred.

Digital LHDC may be employed in lengths up to 2km (1999m). The unit has an adjustment to accommodate interposing cables & IS Barrier.

Fig.10

Fig.11

When operated at 24 Vdc, signalling of fire and fault status is by means of volt free changeover contacts. Two sets for each parameter.

The unit can also be operated in a ‘two wire’ mode that emulates the operation of conventional smoke & heat detectors.

The unit may therefore be directly interfaced with fire control panels by connection to fire zone trigger circuits or addressable interface modules.

The relay contacts are disabled when the unit is directly connected to a trigger circuit.

The DIN rail modular form of the unit enables the LDM-519-DDL to be both readily integrated into site specific industrial control equipment cubicles and / or incorporated by OEMs into proprietary fire panels.

Patol can provide a variety of enclosure types and system configurations. These range from single zone cased modules with IP67 ratings, to multi-zone panels with integral power supplies and IS barrier compartments.

The LDM-519-DDL is primarily intended to be used in conjunction with an intrinsically safe shunt diode (zener) barrier.

Galvanic IS barriers cannot be employed.

The recommended IS barrier type is:-

¨ Dual Channel Shunt Diode - a.c.

¨ V    =    15V

¨ Ω    =    100R (per channel)

¨ I     =    150mA

Model MTL7765 is an IS barrier of this type by

Measurement Technologies Limited.   

The MTL7765 permits the LDM-519-DDL unit’s full detector capacity (2km of LHDC) to be installed in the hazardous area for gas groups IIA & IIB. With group IIC the max installed length is limited to 1526m.

For further information refer to the Hazardous Area applications note below, and the LDM-519-DDL  data sheet.

Direct LHDC Connection to Trigger Circuits via IS Zener Barriers

LDM-519-DDL contacts may be used to simply switch Alarm and EOL resistors to a fire panel. The LHDC can be directly connected, however this requires more detailed consideration.

Fire panel Trigger Circuits are configured such that smoke/heat detectors are connected in parallel in a ‘two wire’ scheme. Fig.12

An ‘end of line’ device (EOL) is fitted at the last detector such that any circuit / detector disconnection results in a fault warning.

Fig.12

Fig.14

On fire the load is increased by the initiating detector switching a resistor (Ra). The fire panel registers an alarm on the extra current.

Short circuit faults are discriminated from alarm.

The LHDC may be connected as shown in Fig.13. An alarm ballast resistor Rab may be required to prevent LHDC operation registering as a short circuit fault.

Each of the LHD & interposing cable elements have two principal parameters :-

Total loop resistance - Rlhd - Rih - Ris

Capacitance - Clhd - Cih - Cis

A simplified circuit of the LHDC connection is shown in Figure 14.

Rzt = Combined channel resistance of Barrier.

IS Barrier Considerations

Trigger circuits generally provide a detector supply voltage in the range of 18V to 28V. Open circuit fault monitoring is by means of the EOL device which is normally a resistor (Reol) drawing a small current.

If a barrier of too low a voltage is used the zener (Vz) may draw a current that in effect overrides and disables the EOL open circuit fault monitoring function.

28V - 600R Dual Channel barriers (eg MTL7778) should accommodate most situations, however there are limitations to cable length.

For example with the MTL7778 connected to LHDC in Gas Group IIC, hazardous area cable capacitance (Clhd + Cih) must not exceed 0.083uF. Patol LHDC is 130pF/m which means that the max installable length, with no interposing cable, is 83000/130 = 638m

Alarm Resistance

When the LHDC operates (Fire closed Fig.14) the resistance presented to the fire panel is :- Rlhd + Rih + Rzt + Ris + Rab .  Cable resistance (Rih + Ris) < 50R for 1km of 1mm².

Patol LHDC is 184 R/km - 638m is 117R. For MTL7778 - Rzt = 1k302.

The presented resistance is 50 + 1302 + 117 = 1469 (Rab would not be required). If 1k5 will not register an alarm at the fire panel the MTL7778 is too high in resistance an can not be employed in this configuration.

End Of Line Resistor

The EOL value should be adjusted to accommodate barrier and cable resistances. If a particular fire panel requires a 4k7 EOL, with the above example 4k7-1k303 = 3k397 (3k3).

 

SPECIAL NOTE :   The above information is a guidance note. National / local regulations, standards, and barrier certifications MUST take precedence in any IS system design and implementation. Fullest reference should be made to fire panel specifications and application recommendations to ensure compatibility.

Direct LHDC Connection via Intrinsically Safe Galvanic Isolators

It is possible to use isolator type units such as MTL3000 & MTL4000 series by Measurement Technology Ltd. Models MTL3043 & MTL4061 are recommended by MTL for ’Fire Detector’ applications, however the simple ‘volt free’ nature of the LHDC may make switch monitoring type isolators more applicable. Some isolators require a separate power supply. Specific fire panel specifications should be referenced to determine the most compatible types.

Stainless Steel Armour

UL Approved Detector

Patol Digital Linear Heat Detector Cable is available with two operating temperatures.

UL approval   :   File No. 24081   UTHV Listed

 

Patol’s standard Digital Line Heat Detectors have a chemical resistant nylon sheath.

The detectors can also be provided with an additional Stainless Steel Armouring Braid.

 

 

 

 

LHDC Installation Fixings

Patol Limited.   Rectory Road, Padworth Common, Reading, Berkshire. UK   RG7-4JD

Tel: +44 (0) 118 9701701           Fax: +44 (0) 118 9791700           Email: info@patol.co.uk

The storage plant facility is generally classified as a “Hazardous Area”. The LHDC installed to monitor the plant is connected by Intrinsically Safe Barriers. These IS barriers ensure that, even under fault conditions, ignition of flammable gases due to electrical sparks cannot occur.

The IS barriers, together with monitoring equipment (interface modules / fire panels), must be installed at a location designated as a “Safe Area”. Alternatively an “Explosion Proof” enclosure must house the barriers/interface, with the signals connected via suitably certified cabling to a remote safe location.

Where the fire zone is at some distance from the ‘safe area’ the LHDC may be connected to the IS barriers via an interposing cable.

Patol LHDC can be installed such that a considerable length resides in each fire zone, however two limiting factors must be taken to consideration as follows:-

¨ The certification of any IS barrier used will specify maximum parameters for the characteristic of any connected cable. The capacitance of both LHDC and interposing cable will define the maximum length of the circuit combination.

¨ Fire zoning must be such that the information presented to personnel is meaningful. The coverage of a long pipe / manifold as a single zone may be reasonable, especially if a locator meter is used. However, grouping of a number of small tanks on a single zone may not provide sufficient information for fire fighting to be effectively targeted, even if a distance locator is employed.