Are septics been backed up in toilets and bathtubs for almost 3 months is this harmful to me and my kids breathing this order?

<Moved from Health & Wellness to Plumbing>

This might explain yourconcerns.
Dangers From Indoor Sewer Gasses
I have inspected a number of homes where I would not have dared light a match indoors, much less live there.
What are Sewer Gasses?

Sewer gasses, also called methane, are a byproduct of human metabolism. Everyone knows what it is like when someone passes gas in a room. Well, the process of gas creation from digested food continues long after we flush the toilet. The gasses fill the sewer pipes that are located underground. These gasses must be vented to the atmosphere to prevent them from building up and exploding. This is done through vents on the roof tops of houses called “stack vents.” Sewer gasses are not only explosive, but have some pretty nasty bacteria and virus' attached to the microscopic particles that float within the gas. When inhaled, people and pets can become significantly ill from a variety of diseases.

The Explosive Nature of Sewer Gasses

A decade or more ago, I remember of hearing on the news how sections of Mexico City had exploded because someone ignited the gasses inside the sewer system. For this danger alone, it is wise to assure that all sewer gasses are being properly vented to the outdoors. Anything that can explode, should not be in your lungs. Period.

The Odor of Sewer Gasses

Like any other indoor odor, many people can become accustomed to the smell of sewer gasses. They can be living in homes with seriously contaminated air, and not even know it. Further, the odor of sewer gas does not have to be very strong to affect the homes occupants. Sewer gasses have a rather odd odor. Sorry I cannot put a “scratch n' sniff” on the web site for you. If you have an odd odor that you can't quite put your finger on, it is probably sewer gasses creeping into your house.

How do sewer gasses get into my home?

Sewer gasses will always take the path of least resistance. The stack vents on roof tops allow the gasses to freely vent to the outdoors. The water in the gooseneck traps built into toilets and seen under sinks, tubs, and showers, are designed to make sure the sewer gasses will go out the roof vents, rather than come in through your plumbing fixtures. If you allow these traps to dry out, the gasses can come freely into your home. If you have fixtures that do not get used very often, or if a house has been vacant for a while, the traps will dry out and the gasses will come in. Be sure to run water in the unused plumbing fixtures about every three weeks to keep the traps sealed.

I have also discovered sewer gasses entering where old plumbing fixtures have been disconnected, and where new “rough in” waste pipes have not been properly capped. Another common entry area I see during inspections is nonprofessional plumbing projects performed by the do-it-yourselfers. Still another area is floor drains that have had the clean-out plugs removed, or that have seized check valves due to years of dirt accumulation.

Stack Vent Blockages

Stack vents are supposed to have free flowing air through them 24 hours a day, not only for sewer gas release, but also to supply oxygen for the bacteria that feed on the waste stuck on the interior walls of the pipes. This keeps the walls clean and prevents blockage. The free flow of air also helps toilets to flush better and waste pipes to drain faster without chugging or gurgling. By the way, if your toilets do not seem to flush properly, or if your drains chug or gurgle, you should inspect the vents on the roof.

I have inspected many homes where the stack vents were blocked off accidentally by falling tree leaves. I have also seen them choked shut from squirrels that try to hide walnuts by dropping them down inside the vent pipes. This causes the gasses, and sometimes stench, to gurgle up and into the house through plumbing traps due to the pressure buildup inside the pipe system. These vents should be periodically inspected where mature trees or squirrels are present

By Building Inspector and Indoor Air Specialist, Dan Schilling
© Copyright 2001 Residential Inspections LLC, All Rights Reserved

Here is another link: Indoor Air -- Sewer Gas

You can also Goggle the individual components: e.g. MSDS methane to get the hazzards of that particular component.