Using only one ascender? - Petzl Netherlands

Using only one ascender?

One ascender is not trustworthy; it is recommended to use two ascenders together and/or to use a backup belay system.


  • Carefully read the Instructions for Use used in this technical advice before consulting the advice itself. You must have already read and understood the information in the Instructions for Use to be able to understand this supplementary information.
  • Mastering these techniques requires specific training. Work with a professional to confirm your ability to perform these techniques safely and independently before attempting them unsupervised.
  • We provide examples of techniques related to your activity. There may be others that we do not describe here.

1. One ascender is not trustworthy

Trusting the belay to a single ascender in motion on the rope is risky.

There is a risk of the ascender coming off the rope:

Accidental opening of the safety catch is possible while ascending.

There is a risk of the ascender slipping on the rope:

Excessive mud or ice on the rope, holding the cam open due to poor hand positioning, foreign objects interfering with the cam (branches, pack straps or clothing), worn teeth...

There is risk of disconnecting the ascender's lanyard, if the carabiner opens (rubbing).


Breaking strength is not an issue when a single ascender is used by one person.

All of the certification tests, and Petzl's internal tests, are done on a single ascender.


When an ascender is weighted on a rope, it is nearly impossible to cause it to disengage or slip. It's when the ascender is unweighted and/or moving on the rope that there is a risk of slippage or separation from the rope.

2. Differences between a chest ascender and an ascender on a lanyard

Differences between a chest ascender and an ascender on a lanyard

Chest ascender

The chest ascender is connected directly to the harness without extension. Its stable position allows for good rope glide.

The user takes care to avoid creating a loop of slack when progressing, thus maintaining a low potential fall length.

Chest ascender

Ascender on a lanyard (or progression ascender)

A lanyard offers more freedom of movement to the user, who can mistakenly find themselves above their ascender or with a slack lanyard. This creates potential for a fall. As with the chest ascender, one must also monitor the tension in the rope between the ascender and the anchor. Any loop of slack is dangerous.

Ascender on a lanyard


The ascender standards partially cover the risk of falling on a slack lanyard.

The EN 12841 type B standard (ascenders for work): fall test on a dynamic lanyard, ascender on a semi-static rope at 1 m from the anchor. Test with the mass engraved on the ascender (140 kg for ASCENSION, BASIC, CROLL on compatible rope diameters greater than 10mm).

EN 567 standard (ascenders for sport): no fall test.

Petzl's internal testing complement the requirements of the standards by being based on realistic usage scenarios.

These tests ensure that the ascenders do not tear the rope in the most unfavorable conditions (fall of the length of the lanyard, 1 m from the anchor, 80 kg dummy, ropes of compatible diameters).

3. Different modes of ascender use

Rope ascent

The user is hanging on a progression rope.

The recommended rope ascent system includes a chest ascender (CROLL) and an ascender on a lanyard (BASIC, ASCENSION).

As a single ascender is not trustworthy, it is recommended to use two ascenders, both attached to the harness.

Rope ascent

Progression along a fixed rope

The user is on their feet, using one or more ascenders for self-belay and as an aid to progression.

The user has their hands free to slide the ascenders along the safety rope, while always keeping it taut.

If there is a low probability of a fall, using one ascender is possible; the rope must always stay taut between the ascender and the anchor.

Progression along a fixed rope

Self-belayed climbing

The user is focused on climbing, belayed by ascenders that follow their progression. The user does not have their hands free to manage ascender position and rope tension.

A fall is likely in this technical climbing situation, so it is recommended to use two ascenders attached to the harness.

This particular ascender use situation is detailed here:

Self-belayed climbing