/ by Gianni Chiari /

This month Gianni Chiari examines the delicate concept of ‘residual risk’.

Part 4 (Read Part 1, Part 2, Part 3)

In the previous articles we discussed the most important aspects of the activity known as “risk assessment”, which has become the cornerstone of the safety management strategy. I will now continue on the same topic, using as I have done so far simple and informal language, convinced that the priority is to help everyone understand the concept (even those who do not have specific technical experience).

The aspect I want to examine here is residual risk. As always, technical standards help us understand what this involves. Let’s start from the definition reported in EN ISO 12100:2010 Safety of machinery — General principles for design — Risk assessment and risk reduction, which reads as follows:

Residual Risk: risk remaining after protective measures have been implemented.

There is a lot of discussion about residual risks and the level of acceptability. In an advanced society, and one that is in many ways more sensitive, or should I say more ‘litigious’ than in the past, the level of acceptability of residual risk and possible damage has dropped significantly. Nowadays we tend to sue and claim damages for minor matters; I do not wish to judge whether this is good or bad, however the fact is that residual risk must be considered very carefully.

Do you remember from my December article, the figure above which also refers to Note 2 in the definition I just mentioned above?

Basically, this figure states that the designer must adopt the measures in a certain order, namely:

1. Inherently safe design measures
2. Complementary protective measures
3. Information for use.

If possible, first the danger should be eliminated: for example, an external transmission chain where a person’s hand could get caught, causing a serious injury. The designer thus decides to replace it with a reduction drive. At this point, the danger of a hand getting caught in the chain no longer exists; it has been eliminated. FIRST STEP: ONCE HAVING REMOVED THE DANGER, THE RISK NO LONGER EXISTS. 

However suppose it is not possible to eliminate the transmission chain, for several reasons. In this case, a protective measure can be adopted, a so-called ‘guard’. That is, a ‘box’ is installed that encloses the pinions and the chain in order to prevent a hand from accessing it and getting caught and injured. SECOND STEP: COMPLEMENTARY PROTECTIVE MEASURE.

Now the designer only has the last possible option: operating instructions. In the user and maintenance manual, a warning will be added that behind the guard (the box) there are moving mechanical parts, with the risk of body parts being caught in and crushed by the transmission chain. A good and conscientious designer will also affix to the guard a pictogram stating “Moving parts – do not carry out maintenance while the machine is operating or without having first completed the procedure to prepare for maintenance.” THIRD STEP: INFORMATION FOR USE. 

The designer will also warn users of the residual risk of operations during maintenance and commissioning without the guard fitting: risk of entrapment, cuts and other often irreversible injuries. Once this has been done, nothing else is possible.

At this point, it is up to the operator to complete risk reduction through:

• Workplace organization (procedures, supervision, authorizations)
• Supply and use of additional protections
• Use of personal protective equipment
• Training

All of these safety measures help reduce or mitigate residual risk, which however still remains in part, yet at the lowest possible level. It will never be zero (there is no such thing as zero risk) but it will be at an acceptable level.

Maintenance personnel have learned that the designer’s ‘recommendations’ contained in the operating instructions reduce the few remaining residual risks to an acceptable level. It should be reiterated that the work of the designer goes just so far point in the risk reduction and mitigation strategy, doing everything possible; the user must complete the next step.

This combined strategy allows risk to be limited to an at least acceptable level, and if an accident does occur, there should not be irreversible/irreparable damage.

The question now is: how does this approach apply to rides? How acceptable is a residual risk? Based on personal experience, I would say very little. Today, as I said, people file suits for almost nothing. At the same time, guests do not make the slightest effort to improve their own safety by taking appropriate action. Over 80% of accidents on rides are due to incorrect behaviour by riders and the public.

There is a lot to be said about the attention that park visitors pay to the safety warning signs placed near rides. As already mentioned, there is no such thing as zero risk, we need to make sure that nothing happens, and if in spite of everything something does happen, the damage must be limited.

At international level we are working hard on the aspects of rider and public behaviour, as we would like to reduce the already low number of accidents even further. In a near future this could mean increasing the level of restraints (such as belts and safety bars) even on rides where these were not required in the past.

I conclude this article on the residual risk by citing a warning from the American ASTM standard on the responsibilities of guests:

Patron Responsibility

1. There are inherent risks in the participation in or on any amusement ride, device, or attraction. Patrons of an amusement ride, device, or attraction, by participation, accept the risks inherent in such participation of which the ordinary prudent person is or should be aware. Patrons have a duty to exercise good judgment and act in a responsible manner while using the amusement ride, device, or attraction and to obey all oral or written warnings, or both, prior to or during participation, or both.

2. Patrons have a duty to not participate in or on any amusement ride, device, or attraction when under the influence of drugs or alcohol.

3. Patrons have a duty to properly use all ride or device safety equipment provided.

If everyone plays their part, the final result will certainly be positive, as this is the sum of several correct choices and actions.

Taken from Games&Parks Industry February 2019, page 80

Gianni Chiari /  Member of CEN/TC 152, ASTM F 24, ISO/TC254 Technical Committees and “Una Giostra per Tutti” project manager.  info@technicalservices.it