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The Basics of a CNG Cylinder:

The CNG Cylinder, which stores the compressed natural gas, is one of the safest factors of using CNG as an alternative fuel. 

The idea of natural gas being compressed to 3,600 psi and stored in a vehicle tends to frighten some people away.  They're afraid of rupture or explosion, when in fact, the likelihood of either of those occurring is far slimmer with a CNG Cylinder than it would be with a gasoline or diesel tank.

Wise Gas, Inc. only works with approved CNG-cylinders.  Our team is willing to inspect unapproved cylinders for consideration of pursuing approval certification, however, we will not install, repair or provide fuel to any vehicle using an unapproved cylinder for safety and legal reasons.

There is nothing scary about CNG or the cylinders that they are stored in.  The fact is that CNG cylinders are put through exhaustive and extreme tests which include firing bullets at the canister, roasting it over a roaring bonfire and impact tests in which a crane drops the cylinder at multiple impact points.  Compare this to the 1/16th of an inch thick, or plastic, gasoline tanks in today's vehicles containing a much more flammable and toxic substance.

It is, however, important to understand the cylinder and the basic safety facts - just as it's important to understand an electrical outlet in your home so that you don't stick a fork into it. 

When using CNG, you ONLY want to use the proper authorized cylinder.  NEVER TRY TO PUT CNG INTO ANY OTHER TYPE OF CYLINDER!  CNG is more highly compressed than other options, like propane - putting CNG into a Propane cylinder, for example, would be (and has been) disastrous. 

The general rule of thumb with CNG cylinders is the lighter the tank, the lighter your wallet - meaning lighter cylinders are more expensive.

There are 4 types of CNG Cylinders:

1.  Type 1:  Entirely made of metal (either steel or aluminum).  This is the most cost-effective, but heaviest choice.
 

2.  Type 2:  Metal liner reinforced with composite wrap (either glass or carbon fiber) around the middle of the cylinder ("hoop wrapped").  The liner and the composite each take 50% of the stress caused by internal pressurization.  These cylinders are lighter than Type 1 cylinders, but more expensive.

3.  Type 3:  Metal liner reinforced with composite wrap (either glass or carbon fiber) around the entire tank ("full wrapped").  These tanks are lightweight, but more expensive than Types 1 or 2.
 

4.  Type 4:  Plastic gas-tight liner reinforced by composite wrap around the entire tank ("full wrapped").  The entire strength of the cylinder is composite reinforcement.  This is the most lightweight tank, and likewise the most expensive in comparison to Types 1, 2 or 3.
 

CNG CYLINDER TESTING:

The testing that CNG Cylinders undergo is extreme and should reassure even the biggest worrier.

  • Hydraulic Cycle Pressure Testing (using water).  A leak qualifies as a failure, rather than a full rupture.
     

  • Low Temperature Pressure Cycling:  Hydraulic pressure cycle test while the tank is chilled to -40F, after which the tank is heated to 149F for additional pressure cycle testing.  Pressure cycling simulates the tank being filled and emptied.
     

  • Drop Impact Testing:  Tanks are at dropped from multiple angles and impact points while empty (not full) because this creates the most severe condition.  Abrasions from the impact are acceptable and normal, any rupturing is considered to be a failure.
     

  • Bonfire Test:  CNG Cylinders are designed to "vent" the gas rather than allowing a cylinder to rupture or "explode" when exposed directly to fire.  Because CNG is lighter than air, the venting would create a "torch" effect, burning directly upright for a few brief moments until the gas has dissipated.
     

  • Environmental Exposure Test:  Cylinders are exposed to a variety of elements, including road salt, battery acid, gasoline, fertilizer and more while the tanks are simultaneously pressure cycled.
     

  • Damage Tolerance/Gunfire Test:  While none of us actually expects to be shot at while driving (unless you are prone to bringing out the "road rage" in your fellow drivers), the cylinders are subjected to a gunfire test.
     

  • Vibration Test:  Cylinders are vibrated to simulate driving conditions.
     

  • Hydraulic Crush Test:  Cylinders are pressurized and then submitted to extreme pressure in an attempt to "crush" the tank.
     

  • Drag Test:  Cylinders are "dragged" on roadways.

     

CNG Cylinders:  Fires & Collisions:

 

 

 

This photo shows Type 2 CNG Cylinders involved in a bus fire caused by an Engine Fire.

 

Note the 3 CNG Cylinders lying on the ground beside the bus and 2 on the roof of the bus, blackened and charred, but in tact and not ruptured.

 

 

This Natural Gas Civic was involved in a severe collision and crushed to just behind the driver's seat.  (Remember that in most cases, CNG Cylinders are stored in the trunk or behind the rear seats). 

The driver walked away.

There was no leak and no rupture of either the CNG Cylinder or the CNG Fuel System.  Note the absence of any burn marks or scorch marks.

 

 

 

This CNG Vehicle was hit at a speed over 50 miles per hour by a gasoline-powered vehicle.

The Gasoline tank ruptured on the gasoline-powered vehicle and ignited, spreading flames across both cars.

The CNG Cylinder (shown in the photo) safely vented the CNG into the atmosphere.  The tank did not explode or rupture.
 



This series of photos was taken by Wise Gas, Inc. personally when we had the opportunity to thoroughly inspect this municipal truck.

Strobe-style headlights had been installed on this city-owned vehicle and caused an electrical fire.  The entire cab and bed of the truck was engulfed in flames.  The driver walked away, unharmed.

The plastic covering over the CNG Cylinder melted and burned away, exposing a large CNG Cylinder directly to the flames.

As you can see in this photograph, and the following images, the tank remained perfectly intact.  No rupture or Explosion.

 

 

 

This photograph shows a closer look at the exposed CNG Cylinder and melted protective covering.