Quick recognition
Mercaptan odor — sulfur, rotten eggs, garlic
Ethyl mercaptan is detectable by most people at roughly 1 part per billion — far below the propane LFL of 21,500 PPM. If you smell it indoors and the burners are off, you have a leak. Note: chronic smokers and older adults have reduced odorant sensitivity; relying solely on smell underestimates risk.
LP gas detector alarm (typically continuous tone or rapid beep)
RV-specific LP detectors mount at floor level (vapor sinks) and trigger at roughly 25% LFL — well before flammable concentration. The alarm pattern differs from CO and smoke — read the unit's manual at install. Battery-backup-fed detectors can chirp at end-of-life (5-10 year sensor lifespan, same electrochemistry constraint as CO).
Audible hiss at a fitting
Loud hissing indicates a large leak (regulator vent stuck open, severed line, failed flare). Quiet hissing audible only at close range indicates a slow leak at a joint — typical of an over-torqued flare fitting or a degraded rubber hose connection.
Yellow flame or sooting at a propane appliance
Properly burning propane shows a blue flame with a small yellow tip. A predominantly yellow flame indicates incomplete combustion (insufficient air, dirty burner, partial obstruction) and produces orders of magnitude more carbon monoxide as a byproduct. Service the appliance before next use.
Frost or icing at the regulator or a fitting
A large leak causes adiabatic expansion that condenses atmospheric moisture into frost or icing at the leak point. The leak is significant enough to see — evacuate and shut off.
Hissing or popping inside the cabin with no appliance running
A leak inside a cabinet, behind an appliance, or in a concealed line. The fact that you hear it without an appliance running confirms the source is upstream of the appliance shutoff and downstream of (or at) the tank service valve.
Response protocol
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1. Eliminate ignition sources before anything else
The fatal pattern is the occupant who opens a window to ventilate but flips the light switch en route — the switch arcs, the cabin vapor concentration is in the flammable range, deflagration follows. Hands off switches. Do not start the engine. Do not use a flashlight that lacks an intrinsically-safe rating. Open doors and roof vents on the way out, no other electrical actuation.
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2. Evacuate upwind, headcount
Move 50+ feet upwind of the rig. Vapor is heavier than air and pools; you want height, distance, and wind direction working for you. Account for every occupant and pet.
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3. Shut off the tank from outside
Both cylinders if twin-rack, or the ASME onboard tank service valve. Turn clockwise until firm — propane valves are designed to seat firmly; do not overtorque, but do close fully. The valve handle is on top of the cylinder; the ASME service valve is inside the LP compartment usually painted yellow or labeled.
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4. Ventilate aggressively after the source is off
Open all windows, both entry doors, and roof vents. If safe to reach a 12V roof fan from outside (via an awning support or step), turn it on — but only if reachable without entering the cabin. Cross-flow ventilation typically clears the cabin in 30-60 minutes; without cross-flow, vapor pools and persists for hours.
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5. Call 911 + fire department
Even a self-resolved-feeling leak warrants a fire-department combustible-gas meter sweep before re-entry. Tell dispatch the leak source if known, the cylinder shutoff status, and any symptoms in occupants. Fire crews carry MSA / Dräger / Industrial Scientific 4-gas meters that read combustible gas in % LFL.
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6. Soap-bubble test every joint after the fire crew clears the cabin
Mix dish soap and water 1:3 in a spray bottle (commercial leak-detector solution is also available). With the tank reopened and appliances OFF, spray every fitting — cylinder valve neck, regulator inlet and outlet, every flare fitting along the distribution line, every appliance shutoff. Active leak = growing bubbles. Document the leak point before calling a tech.
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7. Schedule a qualified LP-system inspection before next overnight
An RVDA-certified RV technician (rvda.org locator) or a propane-industry-trained tech can perform a manometer pressure-drop test — pressurize the system to 11 inches water column, isolate from the tank, and time the pressure drop. A correctly tight system holds pressure for several minutes. The test catches leaks too small for soap bubbles to find.
Prevention
Install an RV LP gas detector — at floor level — and replace on date code
NFPA 1192 §6.4 requires a listed LP gas detector in every RV with a propane system. The detector mounts low to the floor (vapor sinks) — typically 6-18 inches above the floor near the propane appliances. Like CO alarms, LP detectors use electrochemical sensors with a 5-10 year service life. Check the date-of-manufacture sticker; the test button verifies circuitry and battery, NOT sensor sensitivity. Replace on the manufacturer's date schedule.
DOT cylinder requalification — 12 years from manufacture, then every 5 years
Per 49 CFR §180.205, portable DOT cylinders (typically 20 lb or 30 lb on a travel trailer or fifth wheel) must be requalified at 12 years from the original date of manufacture and every 5 years thereafter. Look for the date stamp on the cylinder collar — month/year in the format 'MM-YY'. Many fill stations refuse to fill expired cylinders; bring the cylinder to a propane dealer for the requalification check and a new date stamp.
ASME onboard tanks have different rules — no requalification but inspection at title transfer
ASME tanks (permanently mounted on motorhomes per ASME Code Section VIII) are not subject to the DOT requalification schedule. They are inspected at original manufacture and again at major service events; NFPA 58 §5.2 governs their installation and inspection. If buying a used motorhome, request inspection records and visually check the tank for corrosion, dents, or grinding wear.
Pre-trip soap test of every joint, especially after winter storage
Rubber regulator vents and pigtail hoses degrade with UV and ozone exposure. Annual soap-test the regulator, both pigtails (twin-cylinder racks), every flare fitting, and every appliance connection BEFORE the first trip of the season. Bubbles = leak; replace or re-tighten. This 10-minute test catches the vast majority of slow leaks before they pool.
Travel with cylinder valves CLOSED when crossing tunnels, ferries, and fueling
Some U.S. tunnels (Holland, Lincoln in NYC; Pennsylvania Turnpike tunnels; many others) prohibit LP cylinders open while transiting. Most ferries require valves closed during crossing. Always close LP at the cylinder when refueling the tow vehicle or motorhome chassis — the refrigerator running on LP during fueling has been a documented ignition source for tow-vehicle fires.
Replace pigtail hoses every 5-7 years regardless of appearance
Rubber LP pigtail hoses (the flexible lines between cylinder and regulator on a twin-rack) have a finite life from manufacture due to plasticizer migration and rubber stiffening. Visual inspection misses internal cracking. NFPA 58 and most cylinder dealers recommend 5-7 year replacement; the hoses are $15-30 each, the consequences of failure are catastrophic.
Real case studies
NFPA 58 · Liquefied Petroleum Gas Code · Installation and Use
NFPA 58 is the U.S. governing standard for LP gas installation, storage, transport, and use. The code prescribes container construction, distribution piping, regulator and valve requirements, pressure-test procedures, leak-detection protocols, and installer qualifications. RV LP systems are designed to NFPA 58 + NFPA 1192 §6. Manufacturer certification (RVIA oval at the entry door) signals NFPA 1192 compliance at build time; ongoing compliance requires periodic inspection by a qualified technician.
Lesson: The pressure-drop manometer test (NFPA 58 §7.2) is the gold-standard leak check. Most RVers never see it done. Ask your service writer to include it in the annual propane-system service.
49 CFR §180.205 · Requalification of cylinders
The U.S. Department of Transportation requires portable DOT propane cylinders to be requalified at 12 years from manufacture and every 5 years thereafter. Requalification consists of a visual inspection (per CGA C-6) for corrosion, denting, fire damage, or valve wear, plus optional pressure testing. The dealer applies a new date stamp on successful requalification. Fill stations are required to refuse to fill expired cylinders.
Lesson: Read the collar stamp on every cylinder. A cylinder you bought used may be days from refusal at the next fill station. Requalification is cheap; cylinder replacement is not (current new 20 lb cylinder ~$50, 30 lb ~$80).
Source: U.S. DOT · 49 CFR §180.205
U.S. Fire Administration · Recreational Vehicle Fires Report
USFA's analysis of NFIRS data ranks LP gas (cooking equipment, water heater, furnace) and engine compartment / running gear as the top heat-source categories for RV fires after cooking-fire ignitions. The most frequent LP-related ignition scenarios in the data are improperly stored cylinders, leaks at distribution-line connections, and appliances not service-shut during refueling.
Lesson: Close cylinder valves at refueling. Annual professional service. Test the LP detector monthly and replace at date-of-manufacture lifespan.
Source: U.S. Fire Administration · Residential fire statistics
What authorities don't always tell you
Editorial secrets
Mercaptan odorant 'fades' — your nose stops smelling it after sustained exposure
Olfactory fatigue causes the sense of smell to attenuate after sustained exposure to a single odorant. A slow leak that you smelled when you entered the rig becomes 'normal' after 10-15 minutes — the leak is unchanged but you cannot smell it. Step outside for 5 minutes, then re-enter: if you smell it on re-entry, it is still leaking. This is also why an LP detector is required equipment, not optional.
The regulator vent is supposed to be open to atmosphere — but pointed down
Two-stage propane regulators have a small vent on the underside of the lower body. The vent must be unobstructed (free of mud, debris, insect nesting) AND pointed downward so water does not enter. A blocked vent causes regulator malfunction — over-pressure to appliances, premature lock-off, or in failure mode, regulator rupture. Annual visual inspection. Many regulators include a plastic cover or screen specifically to keep debris out.
Twin-cylinder automatic changeover regulators can mask a leak in one cylinder
A two-cylinder rack with auto-changeover switches to the second cylinder when the first runs out. If the first cylinder is leaking, the regulator may switch over silently, leaving you with an apparently-normal-flowing system while one cylinder slowly empties to atmosphere. Check both cylinder levels monthly with a hand-held scale or magnetic indicator; if a cylinder is emptying faster than usage justifies, look for a leak at its valve or pigtail.
Propane gauges (the magnetic strip-thermometer style) are unreliable
The stick-on magnetic gauges work by detecting the temperature differential between the cooled liquid level and the warmer vapor space — only after running the appliance for several minutes. They are useful as rough indicators but cannot distinguish a half-full cylinder from a nearly-empty one. Hand-held scale weighing (tare weight is stamped on the cylinder collar — typical 20 lb cylinder weighs ~17 lb empty) is the only reliable method.
RV propane refrigerators on LP during fueling have ignited gasoline vapor
Multiple documented incidents at gas stations involve the refrigerator pilot or burner igniting gasoline-pump vapor. The Truckers Friend / RV propane safety community consensus and most state fire-code guidance: close LP at the cylinder before pulling into the fuel island. Refrigerators on absorption-cycle LP take roughly 30-60 minutes to lose cold-hold; cycle through fueling without losing food temperature.
Equipment recommendations
Generic categories — no brand endorsements. Verify current specifications against the manufacturer's documentation.
RV LP gas detector (12V hardwired, floor mount)
Spec: UL 1484-listed RV LP detector. 12V DC. Mounts 6-18 inches above floor (vapor sinks). Listed lifespan 5-10 years from date-of-manufacture sticker. Some units combine LP + CO sensors in one housing; convenient but both sensors share the same replace-by date.
Storage: Permanently mounted near LP appliances (typically galley or near refrigerator) per NFPA 1192 §6.4 and manufacturer instructions.
Soap-bubble leak detector solution
Spec: Commercial leak-detector solution (yellow-tinted, optimized bubble formation) OR DIY: 1 part dish soap to 3 parts water in a spray bottle. Soak fittings, watch for growing bubbles.
Storage: Tool kit, refreshed annually (DIY) or per shelf life (commercial).
Hand-held cylinder scale or magnetic level indicator
Spec: Bathroom scale (set tank on it; calculate fuel weight by subtracting the cylinder's stamped tare weight) OR magnetic temperature-differential indicator (less accurate but quick). Confirms cylinder levels and detects unexpected fast emptying that signals a slow leak.
Storage: Storage bay.
Pigtail hose pair (twin-rack systems)
Spec: ACME / Type-1 quick-connect on cylinder end, flare fitting on regulator end. OEM-spec for your rig. $15-30 each. Replace at 5-7 years regardless of appearance.
Storage: One spare in tool kit for in-trip replacement.
Class ABC fire extinguisher
Spec: Minimum 2A:10B:C. The B rating addresses flammable-liquid + flammable-gas fires (propane). Annual visual inspection; recharge or replace per manufacturer spec.
Storage: Wall-mounted near the entry door, second unit near the galley.
When to call 911 vs ER vs self-care
Call 911 now
- Active visible flame or audible loud hissing from propane source
- LP detector alarm with no obvious source (concealed leak)
- Strong mercaptan odor that persists after closing cylinder valves
- Any occupant showing dizziness, headache, or breathing difficulty after LP exposure (propane is an asphyxiant at high concentrations)
Drive to ER
- First-degree or larger burns from flash ignition
- Documented vapor inhalation with persistent headache or shortness of breath
- Frostbite from direct contact with liquid LP (liquid expansion cools surfaces to -44°F at one atmosphere)
Urgent care
- Minor first-degree burns from contact with a heated regulator or fitting
- Mild lingering headache after a contained event that resolves in fresh air
Self-care at home
- Soap-test reveals a loose flare fitting; tighten with two wrenches, retest, no symptoms
- End-of-life chirp on LP detector — replace the unit
Frequently asked questions
Why does my LP detector go off when I cook with the propane stove?
Likely placement too close to the burner — burner startup releases a brief unburned-fuel puff that the detector reads. NFPA 1192 §6.4 and the detector manufacturer specify minimum distances from any appliance. Relocate the detector per manufacturer instructions (typically 4-6 feet from the burner) rather than disable it; nuisance-disabled detectors are documented in CPSC LP-related fatality reports.
How often should I have the propane system pressure-tested?
Annually as part of the rig's RVDA-certified service, or any time you suspect a leak. The manometer pressure-drop test (NFPA 58 §7.2) pressurizes the distribution to 11 inches water column, isolates from the tank, and times the pressure drop — a tight system holds for several minutes. The test catches leaks too small for soap bubbles. Costs $50-100 at most RV dealers and is the only objective measure of system integrity.
Can I refill my own portable propane tanks at the cabin or at home?
Cylinder refilling requires a licensed propane dealer per NFPA 58 + state regulations in every U.S. state. Self-refilling from a larger tank is illegal in most jurisdictions and unsafe (overfill protection devices, OPDs, must be tested at each fill). Refusing to refill expired cylinders is also a dealer requirement under 49 CFR §180.205. Bring cylinders to a licensed dealer.
What's the difference between a DOT cylinder and an ASME tank?
DOT cylinders are portable, 20 lb / 30 lb / 40 lb capacity, regulated under 49 CFR Part 178 (construction) and Part 180 (requalification — every 12 then 5 years). ASME tanks are permanently mounted (motorhomes), built to ASME Code Section VIII, not subject to DOT requalification but inspected per NFPA 58 at title transfer and major service. Both require the same downstream LP-system integrity practices.
Should I travel with the propane on for the refrigerator?
Owner manuals vary, fire-safety guidance is consistent: close LP at the cylinder when refueling the tow vehicle / motorhome chassis (refrigerator pilot is a documented ignition source for gasoline-pump vapor), and consider closing when transiting tunnels and ferries that prohibit open LP. For ordinary highway driving, many owners run the fridge on LP; the absorption cycle restart after extended off-time can take 30-60 minutes to recover cold-hold.
Is this page medical or legal advice?
No. PickRV reference for general education. Defer to NFPA 58, NFPA 1192, 49 CFR Part 180, the propane producer's safety data sheet, RVDA-certified technicians, 911, and a physician for actual emergencies and compliance work.
Sources
Related safety pages