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4.2 Operation of diesel engines in hazardous zones

The contents of this chapter is based on an OCMA specification No. MEC-1 published onbehalf of the Institute of Petroleum [6 .

There are considerable problems in providing assured protection to diesel engines for use inzone 0, 1 and to a certain extent in zone 2 !"# $%&$ PA'( 1) . The use of permanentlyinstalled diesel engines in zone 0 is unacceptable, and the use in zones 1 and 2 should beavoided wherever possible. If the diesel engine is ade uate and efficiently protected to allelectric, hot surfaces, exhaust systems, etc. they may be located in zone 1 and 2. !ormallythese protection include the provision of an air source from an non"hazardous zone. #owever if this is impracticable, the engine shall be fitted with an automatically operated combustionair cut"out to prevent engine runaways in the event of flammable vapour ingestion.

$obile diesel"engined e uipment should preferably not be used in a hazardous zone, but if this is unavoidable it should be fully protected as for fixed diesel installations or have aminimum of protection and operate under a permit"to"wor% system. The minimum protectionshould be spar% arrestors, hot surface cooling and, in addition for zone 1, an automatic air cut"off.

The following recommendations &table '( are made for protection of diesel engines on drillingrigs which are permanently installed in hazardous zones 1 and 2.

!ature of hazard )ones 1 and 2*ischarge of spar%s fromelectrical e uipment

+tarter pneumatic, hydraulic, spring recoil, inertia or hand start.-ny other electrical e uipment associated with the engine shall

be flameproof & + / ( or intrinsically safe & + 123'(.4lectrical e uipment shall be effectively earthed and bonded tothe main engine frame.

*ischarge of spar%s frommechanical causes

5ooling fan blades shall be made from non"metallic materials.

6eneration and discharge of static electricity from beltdrives

-ll belts shall be of anti"static fire"resistant type.

*ischarge of spar%s or flames from the exhaustsystem

- gas conditioner box and a flame trap shall be installed.-lternatively, the exhaust should be designed to discharge to alocation within a safe zone.

7lashbac% through inductionsystem

8herever possible, air inta%es for engines shall be located in asafe zone. -lternatively, a flame trap should be provided & arber valve(.

4xcessive temperature of exhaust gases and excessivesurface temperature of engineand exhaust system

The surface temperature of the engine and exhaust systemshall not exceed 23095 when tested under full loadconditions. 4xceptions are when free movement of air isrestricted by thermal or acoustic shielding and:or when the

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!ature of hazard )ones 1 and 2auto"ignition temperature of the flammable, determined by-+T$ test *2133" is below 20095. &mobile combustionalfluid methane gas than the engine surface temperature ishigher 30095(

;verspeeding of the enginedue to induction of flammablegas or vapour

- means shall be provided to stop the engine whenoverspeeding is caused by flammable gas or vapour.

;verheating due to failureof cooling water system or lossof lube oil pressure

-larms or automatic shutdown devices shall be provided,actioned by excessive water temperature and lowlube oil pressure.

4xcessive engine vibration -n alarm or trip device to protect the engine from excessivevibrations should be considered.

4xplosions in engine cran%caseection pump and governor where fitted should beso designed that reverse running of the engine is not possible.

Table 9. =ecommendations for protection of diesel engines in hazardous zones &;5$-$45"1(.

=igs which have been designed and e uipped with diesel engine power supply to the

drawwor%s, rotary table and mud pumps according to -?I =? 300 do not always complywith hazardous zone restrictions as defined under the I? 5ode.