Quick answer
A safety containment cable is a steel cable threaded through the center of a garage door extension spring and anchored at both ends, so that if the spring breaks, its pieces stay on the cable instead of flying.
DASMA defines it as a cable threaded through an extension spring to retain the spring if it breaks. Torsion springs on a shaft are contained by the shaft; extension springs need these cables.
Quick facts
The key facts about Safety Containment Cable, with sources:
- DASMA definition
- Cable through an extension spring that retains it if it breaks 1
- Other names
- Safety cable, restraining cable, safety spring containment 1
- Needed on
- Extension spring doors 2
- Not needed on
- Torsion springs, which the shaft contains 2
- Inspector check
- Are springs restrained by a cable or shaft? 2
- Before an opener
- Springs must be restrained by a cable or shaft 4
Key takeaways
- Every extension spring should have a cable running through its center.
- The cable holds the pieces of a broken spring so they cannot whip through the garage.
- It does not lift the door; the lift cables do that.
- You can check for it from the floor with the door closed.
- Adding or replacing one is technician work because it sits next to loaded springs.
What a containment cable is
Extension springs run along the horizontal tracks and stretch to store the door’s weight. They hold the most energy when the door is closed. If one snaps, the broken ends can fly with real force. Amarr warns that a broken extension spring can send parts around the garage, through windows or car windshields 5.
A containment cable is the cure. DASMA defines it as a cable threaded through an extension spring to retain the spring if it breaks 1, and lists restraining cable, safety cable, safety spring containment and spring containment device as other names for the same part 1.
It is a separate cable from the lift cables. It runs straight through the spring’s coils and is fastened to fixed points at each end, usually the track hanger at the back and a bracket near the front.
How it works
The cable does nothing while the spring is whole. The spring stretches and relaxes around it on every cycle. When the spring breaks, the coils have nowhere to go except along the cable, so the pieces slide and stop instead of being launched.
Torsion springs do not need this part. DASMA’s home inspection checklist explains that torsion springs are mounted on a shaft, which inherently provides containment, while extension springs must be contained by a secure cable running through their center 2.
Extension springs
Containment methods
Example: DASMA’s inspection item
DASMA’s checklist for home inspectors and consumers includes containment as its own item 2.
| Item | What to do | Pass if |
|---|---|---|
| 3. Spring containment | From inside, door closed, look at the springs | Springs and attachment parts restrained by a cable or shaft |
| If extension springs | Look for a secure cable through the center of each spring | Cable present on both sides |
| If torsion springs | Confirm springs are on a shaft | Shaft present |
- Door closed
- Extension or torsion springs?
- Cable through each extension spring
- Both ends of each cable anchored
- No frayed containment cable
- Spring warning labels present
Source: [2]
DASMA says if any answer is “no,” stop and urge the homeowner to contact a trained technician 2.
Where to look
Stand inside with the door closed. Look above each horizontal track. If you see a long spring running toward the back of the garage, look through its coils: a thin steel cable should run the full length of the spring and be fixed at both ends.
If you cannot see one on either side, the springs are uncontained. DASMA also checks for a spring warning label and labels near the bottom brackets 2.
Containment before an opener goes on
DASMA lists containment among the checks to make before installing an opener: counterbalance springs and their attachment components must be restrained by a cable or shaft 4. An opener makes the door cycle more often and with less attention, so an uncontained spring is a bigger risk on an automated door.
If you are buying a new opener for an older door with extension springs, ask the installer to confirm containment cables first.
Why a broken extension spring is so violent
An extension spring works like a very stiff rubber band. With the door closed it is stretched to its longest, holding enough energy to help lift the whole door. That energy is spread along the full length of the spring, which can run several feet along the track.
When fatigue finally cracks the wire, the two halves snap back toward their anchors at once. Without anything running through them, the loose ends and any attached hardware, such as the pulley or the hook, can be thrown.
That is the hazard Amarr describes 5, and it is why the inspector checklist treats containment as its own item rather than a detail of spring condition 2.
Fatigue cracks are invisible until the break, so a spring that looked fine yesterday can fail today. DASMA’s spring guidance notes rust and nicks speed fatigue 3. Containment is the protection that does not depend on predicting when.
Containment cables vs broken cable devices
Two different safety parts deal with two different failures. A containment cable handles a broken spring.
A broken cable device handles a broken lift cable: DASMA defines it as a bottom fixture intended to prevent a door from falling if a cable breaks, and a cable safety device as one designed to slow or stop the door’s descent in that event 1.
A door can have one, both or neither. On extension spring doors, containment cables are the expected baseline. Broken cable devices are more common on commercial doors and heavier residential doors. Ask a technician which your door has.
Where containment came from
The industry’s counterbalance standard started with extension springs. DASMA explains that ANSI/DASMA 103 grew out of NAGDM 103, written in the 1970s by DASMA’s predecessor as a voluntary standard for testing extension springs, and was later expanded to cover torsion springs and counterweights 6.
The revised standard also requires tensioned components to be non-removable under tension, need special tools to remove, or be red with warning labels 6.
Containment cables follow the same idea: make the failure that will eventually happen a contained one. Springs wear out by design; what matters is that their failure hurts no one.
Containment through conversion
Some owners choose to remove the need for containment cables altogether by converting to torsion springs. The shaft then provides containment by design 2.
A conversion changes springs, adds a shaft, drums and a center bracket, and needs enough headroom above the door.
It is a bigger job than adding cables, but it also brings the even lift of a single shaft.
What the cable does and does not do
Limits of containment
A containment cable only works if both ends stay anchored and the cable is intact. A frayed or loose containment cable can fail when the spring does.
It also does not stop the door from dropping on the broken side; with one spring gone, that side is unbalanced, and the door should not be operated 2.
What drives the cost
No prices here; see the cost guide.
- Adding cables to a door that lacks them.
- Replacing springs at the same time if they are old.
- Converting to torsion, which removes the need for containment cables.
How a technician fits containment cables
Professional work: the springs are under tension.
- Raises and secures the door so extension springs are at their least tension.
- Threads a cable through each spring.
- Anchors each cable at the rear hanger and front bracket.
- Checks that the cable does not rub or bind the spring in motion.
- Lowers the door and checks balance 2.
Owner checks
- Look for the cable through each extension spring every few months.
- Confirm both ends are still anchored.
- Watch for fraying or rust.
- Never remove a containment cable.
If you have no containment cables
Treat it as a priority fix. Until then, keep people and cars clear of the springs’ path when the door is closed and moving, and do not hang anything near the springs. If a spring breaks, stop using the door 2.
Do not fit cables yourself
Threading a cable through an extension spring means working beside a loaded spring and its pulleys. DASMA says spring work must be done by a trained door systems technician 2.
Standards
Containment is part of the voluntary ANSI/DASMA 103 counterbalance standard’s focus on tensioned components 6 and appears in DASMA’s inspector checklist and pre-installation guidance 2 4. No federal law requires containment cables on existing doors, but inspectors routinely flag their absence.
Containment cable vs related parts
| Part | Job |
|---|---|
| Containment cable | Retains a broken extension spring 1 |
| Lift cable | Lifts the door |
| Extension spring | Stores the door’s weight by stretching |
| Torsion shaft | Contains torsion springs 2 |
| Broken cable device | Bottom fixture that stops a fall if a lift cable breaks 1 |
Myths about safety cables
Older homes
Older homes are the most likely to have extension springs without containment cables. Home inspectors using DASMA’s checklist flag it 2. Coastal homes should check cables for rust more often.
What to do
Check today. If cables are missing or damaged, book a technician to add them, or ask about converting to torsion springs. See extension springs.
Two minutes, door closed
Stand under each horizontal track and look through the spring. If you see daylight and no cable, call.
Questions about Safety Containment Cable
What is a garage door safety cable?
A steel cable threaded through an extension spring and anchored at both ends. DASMA calls it a containment cable; it retains the spring if it breaks.
Do I need safety cables on my garage door?
If your door has extension springs, yes. Torsion springs on a shaft are contained by the shaft and do not need them.
How do I know if my springs have safety cables?
With the door closed, look through each extension spring above the tracks. A thin cable should run the full length and be fixed at both ends.
What happens if an extension spring breaks without a safety cable?
Pieces can fly across the garage. Amarr warns they can go through windows or windshields.
Are safety cables the same as lift cables?
No. Lift cables carry the door; containment cables only retain a broken spring.
Can I install safety cables myself?
No. It means working beside loaded springs. DASMA says spring work must be done by a trained technician.
Do home inspectors check for safety cables?
Yes. DASMA’s home inspector checklist asks whether springs are restrained by a cable or shaft.
Should I add safety cables before installing an opener?
Yes. DASMA lists spring containment among the checks before an opener is installed.
Do torsion springs need containment?
They are contained by the shaft they are mounted on, per DASMA.
Is a containment cable the same as a broken cable device?
No. A containment cable retains a broken spring. A broken cable device is a bottom fixture that DASMA says is intended to keep the door from falling if a lift cable breaks.
Can converting to torsion springs replace containment cables?
Yes. Torsion springs on a shaft are contained by the shaft, so a conversion removes the need for containment cables. It needs room above the door and is a bigger job.
Can a containment cable wear out?
Yes. Check for rust and fraying, and that both ends stay anchored. A damaged cable may not hold a breaking spring.
Sources
- DASMA Technical Data Sheet #160, Sectional Garage Door Terminology, retrieved .
- DASMA Technical Data Sheet #167, Residential Sectional Garage Door and Electric Operator Checklist for Home Inspectors and Consumers, retrieved .
- DASMA Technical Data Sheet #190, Factors Affecting Spring Cycle Life, retrieved .
- DASMA Technical Data Sheet #369, Frequently Asked Questions Regarding Automated Residential Garage Door Systems, retrieved .
- Amarr, Your Complete Guide to Garage Door Springs (Feb 27, 2023), retrieved .
- DASMA, The New DASMA 103 (interview on the counterbalance standard, Door & Access Systems, Winter 1999), retrieved .
- DASMA, “10 Years Ago: Anti-Codegrabbing Technology Announced” (Door & Access Systems, Fall 2004), retrieved .
Expert review
Written by the HyreGarage Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions from DASMA TDS-160; inspection item from TDS-167; pre-installation check from TDS-369; hazard description from Amarr; standard from DASMA’s DASMA 103 article.
Suggest a correction. We fix errors and say what changed.