Natural Gas Has No Odor
The odor that you recognize as natural gas is added to natural gas by the utility company.  That odorant, mercaptan can be scrubbed out as the gas passes through sand or dirt.  It can even be removed as gas passes through a new steel gas pipe until the pipe becomes saturate with it.  Once that happens, the odorant will no longer be removed.  Why is this important?

Gas leaking from an underground gas leak can seep into structures without the normal or with a reduced gas odor.  You might not be able to smell it.  This knowledge should explain why you cannot and should not investigate a reported gas leak without your combustible gas indicator(meter).

Note: Gas Transmission Pipelines, the ones that deliver the gas to your utility, do not have the odorant added.  It gets added by the utility.  IF you respond to a gas leak before it is added it will not have the telltale odor that you expect.  Your combustible gas indicator  will detect it but, you may see dead vegatation around the leak, if in a puddle, you will see it bubbling up out of the water and you may see a dust cloud created by the escaping gas.  

Gas can trick a carbon monoxide alarm

Bring your gas monitor with you when you investigate sounding carbon monoxide alarms.  You need not only your CO monitor,  you also need your gas meter.   CO alarms can be triggered by natural gas.  If the odorant has been scrubbed out of the gas, you would think that the CO alarm was defective, and might leave a hazardous condition in in the home when you take up from the  "unwarranted" CO response. 

Explosive Range 
Te explosive range of natural gas is between 5% and 15%.  If the gas level is either above or below those percentages, the gas will not ignite or explode.  Below 5%, the lower explosive limit (LEL),the gas is too lean to burn and above 15% the upper explosive limit (UEL), it is too rich.  Before venting a space full of natural gas that is above the explosive range, you should realize that as the gas vents out of the space, the concentration of gas will lower down to and through the explosive range.  If an ignition source is present, it will ignite or explode.  As you can imagine, that could be unpleasant if you happen to be in the space at the time.

National Grid offers safety and tactical on-line training for firefighters at

The training covers overhead and underground electric, electric substations, solar electric, natural gas pipeline structural fires and emergencies and carbon monoxide.  The learning is via interactive PowerPoint training tools.  Instructor notes are included as well as other support material.  Upon successful completion of quizzes, a certification certificate can be downloaded for each topic. 

I’ve gone through all of the modules and found them very informative and worthwhile.  The course was created with the input of first responders and offers the information that we need, so give it a look.  You can stop the course and come back to it multiple times. It can fit into anyone’s schedule.  Our own safety is up to each and everyone of us, so take the course and improve your survivability at utility incidents.