Hébertisme and Security

A Steel Cable Attached to a Tree

Aerial obstacle courses (moving from tree to tree) rely on a safety approach known as "redundant" or "passive," designed to eliminate the risk of human error (specifically, accidental detachment).

Here is a detailed look at how these various safety pillars work:

1. Smart carabiners (interconnected belay systems)

The greatest danger when working at heights is a participant detaching both carabiners simultaneously while moving between platforms. Smart carabiners (such as those from brands like Clic-it or Bornack) permanently resolve this issue through an interconnected locking mechanism.

•             The mechanical principle:

The two carabiners are linked to each other via an internal metal cable (sheath) or a cam system.

•             How it works:

When carabiner A is opened to be moved, the mechanism automatically locks carabiner B, making it physically impossible to open. Carabiner A must be closed and locked onto the next safety line before the mechanism releases the gate on carabiner B.

•             Result:

The user remains continuously connected to the safety line by at least one anchor point.

2. Continuous Lifelines (CLL)

Unlike smart carabiners, which require the user to manipulate connectors at every tree, the continuous lifeline offers 100% passive safety.

•             Equipment:

The participant is equipped with a single connector—either a slotted hook or a roller trolley (a specialized pulley).

•             Principle:

The connector is threaded onto the steel cable at the very start of the course (on the ground) and cannot be removed until the very end.

•             Navigating obstacles:

To pass anchor points at trees or junctions, the cable runs through metal plates or profiled components known as lifeline guides (e.g., the Vertigo or Kanope systems). The connector’s slot is precision-engineered to slide through these components without ever detaching from the cable.

3. Steel cable strength

The cables used in adventure courses are generally made of galvanized or stainless steel, of aircraft or lifting grade (often the 7×19 type—meaning 7 strands of 19 wires each—which offers an excellent balance between flexibility and strength).

                Standard diameter:

Generally between 9.5 mm (3/8 inch) and 12.7 mm (1/2 inch) for lifelines and zip lines.

                Breaking strength:

A standard 12 mm galvanized steel cable has a breaking load of approximately 80 to 100 kN (roughly 8,000 to 10,000 kg).

                Safety factor:

Standards (such as the European EN 15567 or ACCT standards in North America) mandate a high safety factor (often 4 to 5 for human loads). This means the system is designed to withstand forces far exceeding the maximum impact generated by a participant's fall (which rarely exceeds 6 kN, thanks to energy absorbers and the dynamics of the lanyards).

 

4. Inspecting the health of supporting trees

Trees are living structures that react to external stressors. The selection and monitoring of "pillar" trees rely on a rigorous science (arboriculture) to ensure they can withstand dynamic loads.

Visual assessment (VTA – Visual Tree Assessment)

A certified arborist inspects the tree from root to crown to detect:

•             Wood-decay fungi (which parasitize and rot the wood from the inside).

•             Cracks, cankers, or cavities in the trunk.

•             Dead branches or crown dieback, which are signs of a weakened root system.

Technical testing

If there is any doubt regarding the internal structural integrity of a trunk, advanced diagnostic tools are used:

•             Sonic tomograph:

Sensors are placed around the trunk, and sound waves are transmitted. The speed at which the sound travels allows for mapping the tree's interior and detecting rotten or hollow wood (sound travels more slowly through voids or soft wood).

•             Resistograph:

A fine needle penetrates the wood at a constant speed. The resistance encountered by the needle is measured. A sudden drop in resistance indicates a cavity or an area of ​​decay.

Protecting the tree from installations

To prevent cables from strangling the tree (which would cut off the flow of sap), adventure parks use wooden planks (protective slats) placed vertically between the cable and the bark. The cable encircles the tree by clamping onto these planks, distributing the pressure and protecting the cambium (the tree's growth layer). Additionally, these systems are periodically loosened to accommodate the tree's increase in diameter.