Crankcase Explosion: Understanding the Risks and Safety Measures

Crankcase Explosion: For most large two and four stroke engines, a crankcase explosion is still a cause for concern. It’s among the riskiest explosions that can happen to marine motors. It has the potential to kill people and impair a vessel’s ability to move, leaving it trapped wherever it happens.

Following a particularly catastrophic explosion on board the MV Reina Del Pacifico in 1947 that resulted in the deaths of 28 persons, SOLAS restrictions were implemented to prevent crankcase explosions.

Since then, ships have implemented several detection and preventive systems to either completely eradicate or significantly lower the probability of this phenomena. This post will explain what a crankcase explosion is, explain how it happens, and provide preventative measures.

What is a ship’s crankcase explode?

Crankcase Explosion

The term “crankcase explosion” describes an explosion that happens when oil mist ignites inside an engine’s crankcase. An engine’s crankcase has everything needed for an explosion. The fire triangle is a theory that can help us comprehend it more fully.

Any explosion or fire requires three things to happen. These three combined make up what is referred to as the “fire triangle”: heat, fuel, and oxygen.

For a fire to start, oxygen and fuel must be present in the proper proportions. It won’t ignite if it is either too rich (more fuel, less oxygen) or too lean (more oxygen, less fuel).

Because of this, an explosion does not happen in an engine crankcase until the proper air-fuel ratio is reached, even though all three components are constantly present. Let’s examine the series of actions that culminate in a crankcase explosion.

Crankcase Explosion Causes

Everyone is aware that in order for a fire or explosion to occur, the fire triangle must be complete. These three elements are fuel, oxygen, and heat/energy. When all three of these components are present in the right amount and within the flammable limitations, the reaction that starts a fire or explodes becomes cyclical.

The oil particles are agitated into tiny particles as small as 200 micrometers in diameter inside the main engine’s crankcase. Not even a bare flame can easily ignite these tiny particles. These tiny particles are reduced in size when they come into touch with a hot point, which leads to the development of mist that is easily ignited by a hot spot.

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All three of the components needed to start a fire are present in the main engine’s crankcase. Air is present as one of the three required elements, lubricating oil is present as the fuel source in appropriate amounts, and heat or energy is generated from a hot spot. Crankcases are therefore the most prone to explosions since they have an excess of all three necessary components.

A Hot Spot: What Is It?

Crankcase Explosion

A hot spot is simply the source of heat created when two metal surfaces rub against one another or when two metal components, like a gear drive and a piston rod, cross head guides, a chain and gland, etc., come into contact. Typically, poor maintenance and insufficient or nonexistent clearing are to blame for the hot area.

These oil particles evaporate and are replaced by smaller particles when the oil comes into contact with the hot region. When these particles come into contact with the colder area within the crankcase space, they travel in that direction and create a white mist. Mist starts to build more and more over time, and when the air/fuel ratio is high enough to surpass the lower explosion limit, the mist comes into contact with the hot point once more and, in the presence of enough temperature, explodes.

The amount of mist created within will determine how big of an explosion it is. While the secondary explosion may have more severe and catastrophic repercussions, the original explosion may have been moderate enough to lift the crankcase relief valves.

Secondary explosion

A shock wave is created by the main explosion and it travels through the crankcase faster and farther. The breaking impact of this shock wave produces more fuel for ignition, which further reduces the size of oil droplets. A low pressure area is now trailing the pressure front and attempting to draw in more air from the exterior. This permits leaky relief valves or piston glands to let air into the scavenging space.

When the hot spot comes into touch with the fresh air and fuel supply created from the first explosion, another explosion occurs. This explosion is very intense since there is now a lot of fuel present. Engine plating sustains extremely serious damage from this explosion, which is referred to as a secondary explosion. Many lives have been lost in the past as a result of crankcase explosions.

Thus, the secret to preventing such explosions is regular maintenance and inspections.

Safety devices for crankcase explosions

To stop crankcase explosions, marine diesel engine manufacturers have incorporated numerous safety features. These devices need to be carefully maintained and watched over in order to identify hot areas and oil mist in a crankcase and take appropriate action.

Among the typical safety gadgets are:

  • Oil mist detector
  • Crankcase relief valve
  • Crankcase exhaust fan
  • Breather pipe
  • Lube oil temperature sensor
  • Bearing temperature sensor

What’s the best way to prevent crankcase explosions?

When spotted on time, there are many tell-tale signs of an impending crankcase explosion. Other signs just need careful observation, while others require special instruments.

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For safe and incident-free main engine operation, everyone in the engine room needs to know these signs and symptoms.

Signs of crankcase explosions without instruments:

  • Use an infrared or touch thermometer to check for hot spots

  • Engine running weird

  • There’s an abnormal sound or vibration in the main engine

  • White mist or its smell coming from breather pipes or drain cocks

Signs with instruments for crankcase explosions:

  • Temperature increase in bearing lube oil

  • Temperature increase in bearings

  • Alarm for oil mist detector

  • Crankcase relief valve operation and smoke, sparks, and oil exit

  • Crankcase lube oil is bad

  • Excessive clearances between mating parts like piston/liner, piston rod/stuffingbox, engine bearings. So on.


Crankcase explosions still happen. 143 crankcase explosions were reported to Class LR between 1993 and 2001. LR had 20% of the world’s ships at the time.

Extrapolating to 100%, we can say there were 715 crankcase explosions in these 11 years, or 65 a year. Statistics only cover reported incidents where the damage was bad enough to be reported.

It could easily be over 3 incidents a week in reality. Diesel, gas, and dual-fuel engines still have a high risk of crankcase explosions in 2022. It’s a very real possibility, even in well-maintained engine rooms.

Still, crankcase explosions are preventable. It’s possible to prevent crankcase explosions if the crew keeps an eye out for the causes. To stop the condition from getting worse, you have to take immediate and effective measures.

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