Primary Monitored Gases in Household Gas Usage: Defining the Targets for Monitoring

The main types of gases used in households and their associated risks are as follows:

1. Natural Gas (Primary Component: Methane, CH₄)

● Prevalence: Accounts for over 70% of urban residential gas supply in China, delivered via pipelines.

● Risk Characteristics: Methane is a colorless, odorless, and highly flammable gas with an explosive limit of 5%–15% (by volume) (i.e., when its concentration in air falls within this range and encounters an ignition source, an explosion can occur). Once leaked, it tends to accumulate in enclosed spaces (e.g., kitchens, or kitchens connected to bedrooms). Reaching the lower explosive limit (5%) is sufficient to trigger an explosion. Although methane itself is non-toxic, high concentrations can displace oxygen, leading to oxygen-deficient asphyxiation (when oxygen levels drop below 19.5%, symptoms such as dizziness and fatigue may occur in humans).

2. Liquefied Petroleum Gas (LPG, Primary Components: Propane, C₃H₈, and Butane, C₄H₁₀)

● Prevalence: Commonly supplied in bottled form (e.g., gas cylinders), often used in older residential areas or households without piped gas access.

● Risk Characteristics: Propane and butane are heavier than air (air density ≈1.2 kg/m³; propane ≈2.0 kg/m³; butane ≈2.5 kg/m³). When leaked, they accumulate near the ground (e.g., inside cabinets, along floor tiles), making them more prone to build up to explosive concentrations in low-lying areas. Their explosive limits are 1.5%–9.5% (propane) and 1.8%–8.4% (butane)—broader than methane, posing higher risks. Similar to methane, LPG leaks can also lead to oxygen deficiency.

3. Town Gas (Artificial Gas, Primary Components: Hydrogen, Carbon Monoxide, Methane, etc.)

● Prevalence: Still used in a few regions, delivered via pipelines.

● Risk Characteristics: In addition to being flammable (hydrogen has an explosive limit of 4%–75%; carbon monoxide, 12.5%–74%), town gas contains carbon monoxide (CO)—a colorless, odorless, and highly toxic gas. CO binds to hemoglobin 200–250 times more strongly than oxygen, causing hypoxia in the human body (mild poisoning: headache, nausea; severe poisoning: coma, death).

Note: To aid user detection, gas suppliers typically add odorants (e.g., tetrahydrothiophene) to natural gas and town gas, giving leaks a distinctive "rotten egg" smell. However, odorants may become ineffective due to pipeline aging or user olfactory limitations, making gas detection equipment a necessary supplement.