4.2 Safety distances to prevent access by upper limbs

EN ISO 13857 and Safety distances to prevent access by upper limbs

Last edit: 03/03/2023

In this chapter the safety distances to protect upper limbs are detailed

Reaching upwards

The figure shows the case that will be analyzed:

1. Hazard zone

2. Reference plane 

h. Height of hazard zone

The new version of the standard defines the Reference Plane as 
as the level above which people normally stand during the use of the machine or from which they have access to the Hazard Zone.

As explained in the introduction, in order to define the height (h), it is necessary to evaluate the risk associated with the hazard zone.


The height of hazard zone will vary according to the level of the risk. In particular:

•    Low risk – h = 2500 mm (or higher)
•    High risk – h = 2700 mm (or higher)

Reaching over protective structure

Consider the figure nearby, being:

a. Height of the nearest point to the Hazard Zone
b. Height of protective structure
c. Horizontal safety distance to Hazard Zone 
1. Hazard zone (nearest point)

The Standard gives two tables from which obtain the distances, one in case of low risk and the other in case of high risk. Tables are shown below.

Table 1 – Reaching over protective structure (Low risk)

Table 2 – Reaching over protective structure (High risk)

Reaching around

Table 3 shows examples of fundamental movements for persons of 14 years and above (approximately 1,4 m height and above). Safety distances shorter than 850 mm (see Table 4) may be used when the obstacle limiting the movement is at least 300 mm long.

Table 3 – Reaching around

Reaching through regular openings

About the reaching of hazards through openings, the Standard distinguishes between persons of at least 14 years old and persons of at least 3 years old (for public places). Clearly, in the second case, smaller dimensions of the limbs are taken into account.

According to the dimensions of the opening and its shape, the Standard defines at which distance the hazard shall be, in order to forbid its reaching by means of fingers, hands or arms. In case of children, this distance is higher. The tables are shown below.

Table 4 – Reaching through regular openings (14 years old or above)

Table 5 – Reaching through regular openings (3 years old or above)

Just to do an example, consider Table 4 and assume there is a square opening with the side included between 12 and 20 mm. Thus, a finger could completely pass through such an opening. In this case, the hazard zone shall be at least 120 mm far from the opening.

In cases where e it is more than 120 mm or 100 mm in the case of children, the standard requires to consider what is written for the contact reaching over the protective structure.

Reaching through irregular openings

In the case of irregular openings, the following steps shall be carried out in the order given. 
a)    Determine:
•    the diameter of the smallest round opening,  
•    the side of the smallest square opening, and 
•    the width of the narrowest slot opening into which the irregular opening can be completely inserted 
b)    Select the corresponding three distances according to either Table 4 or Table 5. 
c)    The shortest safety distance of the three values selected in b) may be used.