For machine safety in the manufacturing industry, compliance is only the beginning. To truly safeguard workers and ensure operational integrity, organisations must understand and apply the intent behind machine safety standards and understanding the technical text can be key to this.
The AS/NZS 4024 series of standards offers a comprehensive framework, and when the European standards are also considered there is a vast quantity of information. Within this expansive library of documents lie the “hidden nuggets” — requirements around risk assessment, machine guarding, and functional safety that are not well publicised yet are very valuable for the effective risk management of machinery.
This article explores valuable but often-missed elements in machine risk assessment, such as inherently safe forces, and reaching under/through openings, rotating shafts (AS 4024.3410 / EN 415-10), and emerging robotic standards. We’ll also connect these insights to functional safety—namely, achieving the appropriate Performance Level (PL) as per AS/NZS 4024.1503 / ISO 13849-1. Understanding these areas empowers decision-makers and designers to understand with more certainty the risks present so the right safeguards can be installed and residual risks better understood by the PCBU’s.
Inherently Safe Forces – The Hidden Limits in AS 4024.3410
It’s easy to assume that low energy movements of machinery is safe. However, what is low? AS 4024.3410 clarifies this by defining quantitative limits for force, energy, and pressure during human-machine interaction. If these thresholds are exceeded—even at low speeds—the result can be significant injury. However, the corollary to this is if you keep forces to below these levels the hazard is inherently safe and you can consider no guarding at all! Consider a reject arm on a packing line removing underweight product. If a suitably small cylinder is used, a tunnel guard to safeguard any associated crush hazards may not be required.
It’s important that your Hazard ID and Risk Assessment is systematic and thorough to identify this hazard but investigate the forces so you can be informed in what level of safeguarding is required. While AS 4024.3410 is related to packaging equipment the values are universal and you should consider applying them to risk assessments on other types of equipment.
Slow doesn’t always mean safe. Machinery designers must incorporate hazard identification and risk assessment methods that account for force limits early in the lifecycle.
Speed of movement & Avoidance – When is something ‘slow enough’
Another easily overlooked factor is speed of movement. A hazard can become inherently safe if it is slow enough and the ‘possibility of avoidance’ is one factor that makes up the inherent risks associated with a hazard before any safeguards are wrapped around that hazard. ISO 13849 requires a risk assessor to determine this possibility of avoidance in determining the required Performance Level (PLr). But at what speed does an individual have sufficient time to avoid the hazard? In short – it depends. Various international standards have stated that 250 mm/s is suitably slow that you may be able to argue a hazard can be avoided. This is also referenced in AS 4024.3301 related to robots. However, what about for a shear hazard around a guillotine or a press? 250 mm/s is very fast when the moving parts are only 30mm apart. These two differing situations highlight the importance of applying sound risk assessment knowledge and practice when evaluating the safety of your plant and machinery. EN 17449 provides specific information of what the speed of movement should be on a press to be able apply the “Possible to avoid” determination in your risk assessment. Subject to the operational and risk based factors you could consider applying this to other machines.
Reach-Under Guards & Rotating Shafts – Tackling the ‘less risky’ hazards
In other cases it may not be about hazards being made inherently safe, rather – the residual risks may be suitably low that – in certain circumstances that you can demonstrate or justify when further controls may, or may not, be necessary. Take packaging machinery in a food manufacturing plant. AS/NZS 4024.1801 contains some information around reaching through and over openings, yet it is unclear how you might apply these dimensions to reaching under a guard. At what point does the likelihood (and to a certain degree the risk) of someone lying on the floor, sliding up to the edge of the machine and reaching up to hazard become low enough you don’t need further guarding? If you applied AS/NZS 4024.1801 you might think about extending guarding to within 20mm of the floor – which could create food hygiene issues and unintended safety risks if the requirement to clean or maintain a hygienic environment is compromised. The answer to the questions around this specific scenario can be found in AS/NZS 4024.3410 – Safety of packaging machines – General Requirements. The dimensions it gives are all related to human anthropometrics e.g. finger tip to elbow length so they have a degree of universality to them that can be at least considered – again good risk assessment is key – in other non packaging machinery scenarios.
The specificity of thes3000 series AS/NZS 4024 standards can be very helpful. But what happens when a specific requirement of one of these standards has a requirement that is very difficult to meet. AS/NZS 4024.3610 – Safety of machinery – Part 3610: Conveyors – General requirements – states that rotating shaft ends should be covered/guarded. Bearing caps may routinely fall off or custom guards may need fabrication that, in certain environments can introduce other issues – food hygiene issues. Also – if a rotating shaft is smooth and barely extends past the bearing housing – how much risk is there? Where these issues become significant and applying this specific control is potentially not ‘reasonably practicable’ – AS/NZS 4024.3410 comes to the rescue again. In the context of packaging machinery it states that rotating shafts do not need guarding if they are smooth and they only project a very short distance past the bearing housing. There is some inference that the residual risk can be acceptably low. With sound risk assessment in your specific scenario you may be able to argue the residual risk is low enough to not have to fit the problematic covers/guard.
Functional Safety Design – Risk Assess with greater certainty and avoid over-engineering
Some hazards on machinery will require a functional safety solution e.g. light curtains or interlocked guards to adequately minimise the risks associated with that risk. AS/NZS 4024.1503:2014 – Safety-related parts of control systems – General principles for design requires that you determine the integrity/Performance Level (PLr) for that safety function. This considers “Severity” (S1/S2), “Frequency of Exposure” (F1/F2) and “Possibility of Avoidance” (P1/P2). The standard provides some relatively broad descriptions on how to select parameters. Because of this, assessors may err on the side of caution and utilise the more conservative factors. The consequence of that is you may end up over specifying and engineering your safety circuit design – Category 3/PLd safety function can be significantly more expensive to implement than a PLc safety function where Category 1 may be acceptable. ISO 13849-1:2023 – goes into more detail with greater levels of guidance and information around selecting S, F, P values. For instance, P can now be determined on a 5-factor table, meaning you can specify with greater certainty and have a PLr defined that more closely matches the risks concerned.
Conclusions
Leveraging a framework of standards can significantly enhance the quality and credibility of your risk assessments. By drawing on the wealth of guidance embedded across various standards, you can identify controls that are not only effective and justifiable but also practical and cost-efficient. This underscores the importance of ensuring your risk assessors—and any external consultants or contractors—have access to a comprehensive and current library of standards. When used correctly, these resources become powerful tools in shaping sound, defensible risk assessments. Ultimately, robust risk assessment remains the fundamental step towards effective safeguarding, and applying standards thoughtfully is key to getting it right.