Drop Zones vs Tool Tethering - Is tool tethering necessary when we use exclusion or drop zones?

If you’re in the in the process of researching tool tethering options for your at-heights projects you’ve no doubt asked yourself, or been asked by your team, ‘is tool tethering necessary when we use drop zones?’. This is a great question and one that is often raised when we are meeting with on-site crews and demonstrating the GRIPPS range. The short answer is, in a perfect world, no. If a drop zone could be set-up in such a way that any risk of injury or damage was eliminated there would be little need for additional control measures.  The reality is that objects dropped from height almost instantly become projectiles containing enormous amounts of dynamic energy, that is out of control and dangerously unpredictable, particularly if the object ricochets during its fall. 

Drop zones and exclusion zones are an essential component of most dropped object prevention policies however it’s important to recognise the 5 key limitations below: 

1 – Objects don’t fall straight down  

The single biggest challenge with establishing any effective drop zone is the fact that objects don’t fall straight down. Even without deflecting, air movement and object momentum can cause items to stray significantly from their anticipated fall path. To manage this, the recommendation for drops zones are as follows: 

• As a rule of thumb when the working at heights the Drop Zone radius should be between 25% and 50% of the working height.   

This obviously provides a lot of scope for human judgment and site variables, however practically it is often not possible and is also often not adequate. We have been involved in incidents where the final landing place of dropped objects, particularly in windy conditions with lighter items such as phones and small tools, is up to 75% of the actual drop height. 

2 – Deflections  

Deflection of falling items is where the lethal and unpredictable nature of dropped objects is highlighted the most. A recent study conducted by Dean Pratt at the University of Central Qld recorded every drop incident that occurred across a range of projects over a two-year period. The findings in terms of distance items were projected away out the initial fall points are as below: 

Distance out from Drop Point % of Dropped Objects 

 While 88% of dropped objects were recorded as landing with-in 20m out from the initial drop point, all the remaining 12% of incidents are almost guaranteed to be outside of a standard drop zone. It’s worth noting that these incidents are also almost invariably dropped from the greater heights, resulting in…! 

Greater drop height = Greater danger = less effective drop zone!  

3 – Management 

The most effective drop zone becomes ineffective as soon as it is either purposefully or inadvertently ignored. Drop zones require constant monitoring and management for as long as they are being relied on. This policing does obviously involve considerable expense, particularly for long-term height works projects. 

4 – Message to the workforce 

Drop zones, by definition, are a secondary control measure. They are put in place to hopefully minimise the damage that will be cased by an object that is falling and is totally out of control. While secondary control measures are necessary, if they are being relied on with no other control measure, what message does this communicate to the workforce? Reliance on secondary measures alone for personal height safety is unthinkable, we can’t imagine a height worker removing their harness and relying solely on a catch net for safety. If we do only have secondary measures in place for dropped object prevention, does this send a negative message to the workforce about out committal to their safety? 

5 – Luck 

As demonstrated in the study on dropped objects and deflections, approx. 12% of dropped objects are going to fall outside of a drop-zones due to space limitations. This does raise the question as to what we’re relying on for avoiding these incidents causing, damage, injury or even fatality? The answer is LUCK! Once an object has been dropped and happens to deflect outside the drop zone, the only safety measure we have left to rely on is luck. Unfortunately, as we all know too well, luck does run out and there are countless incidents, injuries and even fatalities that have been incurred by objects that have fallen outside of drop zones. 

In summary drop zones are an essential component of a dropped object prevention strategy however, it is critical that other more effective measures are implemented to effectively eliminate the critical risk of dropped objects and to save workers lives.