Do You Know These Tech Terms: Soft Lock and Dead Zone?

This article originated in the July/August 2021 issue of Safe Ride News.

An article in the last issue of SRN focused on how to read an owner’s manual to learn whether a CR feature is a lock-off or not. In response to reader comments and questions, as well as recent recalls, this article builds on that coverage to look at related issues: the concepts of soft locking and dead zones.

Some CPSTs use these terms as shorthand for particular aspects of using seat belts to install CRs. While the terms have become fairly mainstream in CPS jargon, they are confusing to many CPSTs and are entirely unfamiliar to caregivers.
To be clear, SRN does not intend to imply that CPSTs should use these terms nor suggest that technical terms like these be used when educating caregivers. However, based on the feedback in response to the lock-off article, it seems appropriate to clarify the concepts behind these terms.

“Soft” Locking and CRs With Lock-Offs

When a CR is installed using a lap-shoulder belt with a switchable retractor and a lock-off feature is properly engaged, CR instructions do not say that the belt must be switched to ALR (locked) mode. (As explained in the last issue’s article, instructions that do say the belt must be switched are a tip-off that the feature is not actually a lock-off.) However, some people wonder if it’s okay to switch a belt to ALR mode anyway, even though a lock-off is used. They may feel two locking methods are better than one or, perhaps, that locking the belt would reduce the risk of a child having access to the belt and becoming entangled.

It is not inherently dangerous to do this. Per FMVSS 213, CRs are tested using belts that are a fixed length (anchored directly to the test sled device, rather than spooled into a retractor), so they must perform properly using the equivalent of a locked belt to meet the standard. However, it is nonetheless important to always follow CR instructions, and this includes getting permission from the manufacturer to switch the belt if instructions do not say to do so.

Indeed, manufacturers may have valid reasons to recommend against switching a belt to locked mode. For instance, Britax strongly discourages switching the belt when used to install its convertible CRs that have ClickTight (the company’s belt-tensioning feature that also functions as a lock-off) because, when uninstalling the CR, there is a potential for the belt hardware to become stuck within the CR belt path as it retracts. Since a belt in ALR mode can’t be lengthened until fully retracted, dislodging the hardware of a switched belt from the ClickTight’s belt path can be very challenging.

Still, many other manufacturers do allow users to switch the seat belt when a lock-off is in use. Note, however, that such permission seems to be given with more of a shrug than eager encouragement, since doing so is not considered necessary. One usually must ask customer service to get this permission; owner’s manuals typically do not muddy the waters with this unnecessary complexity. Permission can also sometimes be found on approved manufacturer sites. For instance, Chicco gives permission in its installation videos. But, in a review of several CR websites, SRN did not find this to be a common point discussed on installation FAQ webpages.

Getting back to the term “soft lock,” this lingo describes the technique to use when switching a seat belt in situations when the CR is already properly installed using a lock-off. After the CR has been properly installed using the lock-off, switch the belt to ALR mode, and allow it to gently respool without tensioning the belt. Do not make an effort to manually feed more webbing into the spool, as would typically be necessary when a belt in ALR mode is the primary means to hold the CR tightly (no lock-off). Overtensioning the belt when a lock-off is in use could potentially create problems, such as causing the CR to tilt sideways or damaging the lock-off mechanism.

While calling this technique a “soft” lock is shorthand that allows CPSTs to differentiate this method from the typical method (in which the belt is switched and tensioned as much as possible), both techniques result in a locked retractor. Therefore, some people may prefer to describe this method (“lock but don’t tension”) without using the term “soft lock.” The “soft” descriptor is simply a way to indicate the untensioned state that is appropriate when a lock-off is also in use.

A related question is whether a CR user may bypass a lock-off and instead use a seat belt’s ALR mode to hold the belt webbing. Again, the answer varies by CR model and needs to come directly from the CR manufacturer.

Whenever in doubt, remember: If the instructions do not require switching the belt, the CR performs properly with only the lock-off(s) in use. Although manufacturers may permit variations under certain circumstances, they generally prefer their CRs to be used following the instructions that appear in the manual. Veer from these instructions only when truly necessary and when the manufacturer has granted explicit permission.

Watch Out for the “Dead Zone”

A skill technician candidates learn during certification training is how to determine whether a retractor is a switchable or ELR-only type. The “dead zone” is introduced during this part of the training because a lack of awareness of this condition can lead to a misidentified belt type. As CPSTs are taught, when a seat belt is in ALR mode, it stays locked until a certain amount of webbing is retracted; after reaching this point (triggered by a notch in the retractor that engineers call the switch point), the segment of unretracted webbing constitutes a dead zone, in which the belt functions in ELR mode. While the proportion of overall webbing that must retract to arrive at the dead zone can vary from belt to belt, the dead zone shouldn’t be reached until most of the webbing has been retracted.

To prevent the dead zone from causing a student to misidentify a retractor when checking for lockability, the student is taught to pull all the webbing out of the retractor spool and then allow only a few inches of webbing to retract back in before stopping and pulling the webbing back outward. This technique ensures that not enough webbing is retracted to cause the belt system to reset.

If a switchable belt is used properly to install a CR, enough webbing will be routed through the CR’s belt path that the belt shouldn’t enter the dead zone, even when all slack is fed into the retractor for a tight installation.

That’s assuming that the belt is not defective. As noted elsewhere on this page, a wide range of new car models are currently under recall because they may have a switch point that resets the belt to ELR mode too soon (that is, with too much unretracted webbing outside the retractor). This means that their dead zone is too long to be reliable for all CR installations. Read the articles on this page for more details on this widespread recall.

It is also important to consider dead zones when buckling an unused seat belt and switching it to ALR mode as an entanglement-prevention technique. If this precaution is recommended, always ensure that the system will not reset to ELR mode. A buckled belt in the dead zone presents exactly the hazard this technique is intended to avoid. Feed as much slack into the retractor as possible (rather than soft lock); otherwise, vehicle motion could further tighten the belt and possibly cause it to reach the dead zone.