Calculation wizards

Basic principles of safety distances according to EN ISO 13855:2024

Electro-sensitive protective devices such as safety light curtains and safety laser scanners are used to detect a person approaching a danger zone. A correct safety distance between the protective device and the danger zone is crucial here, e.g. to stop a dangerous movement in good time before the person completes it.

The required safety distance is calculated according to EN ISO 13855:2024 using the following formula:

S = K × T + D_DS + Z

S – Safety distance between protective device and hazard area [mm]

K – Approach speed

• Movement of a person: 2000 mm/s (for S > 500 mm)
• Hand and arm movement: 1600 mm/s (for S ≤ 500 mm) 

D_DS – Operating range [mm]; depending on the protective device’s detection capacity and mounting situation. In the orthogonal approach, D_DS is further differentiated as

• D_DO: Reaching over the protective field
• D_DT: Reaching through the protective field
• D_DU: Reaching under a protective field

Basic principles of minimum distances according to EN ISO 13855:2010

Electro-sensitive protective devices such as safety light curtains and safety laser scanners are used to detect a person approaching a danger zone. A correct safety distance between the protective device and the danger zone is crucial here, e.g. to stop a dangerous movement in good time before the person completes it.

The minimum distance is calculated in accordance with EN ISO 13855:2010 as

S_RT [mm] = K [mm/ms] * T [ms] + C_RT [mm]

S_RT – minimum distance between the protective field and point of operation
K – approach speed: access by upper limbs: 2.0 mm/ms / entry: 1.6 mm/ms
T – stop time of the safety function after entry of the relevant part of the body into the protective field [ms]
C_RT – constant additional distance depending on the detection capability of the protective device [mm]

The minimum distance of electro-sensitive protective devices therefore consists of a constant (C) and a dynamic (K x T) component. As even an electro-sensitive protective device can be circumvented by reaching over, the necessary height of the protective field must be determined from a table, like with guards. The necessary distance to the point of operation therefore corresponds to the larger of the two values.

• S_RT (reach-through), calculated based on approach through the protective field
• S_RO (reach-over), with C_RO from the height of the top edge of the protective field and the height of the point of operation

The total stop time T can only be determined with sufficient accuracy by means of measurement. Special stopping time measuring devices are used for this purpose. Measurement of the stopping time is a service offered by Leuze. According to legal requirements, a safety inspection which also includes the stopping time measurement may be performed only by competent persons.

EN ISO 13857 safety distance overview

The following table is used for determining the necessary height of a fixed guard for high-risk applications according to EN ISO13857.

Given: Height of danger zone (a) Horizontal safety distance to danger zone (c) To be determined: The required height of the protective construction (b) Look for the line with the specification of the danger zone height in the left column. In this line, look for the column with the specification for horizontal safety distance to danger zone. The required height of the protective construction is up top in the column head. In case of interim values, the higher value of the protective construction must be used.

Obstacles with a height under 1000 mm are not included since they do not satisfactorily limit the movement.

Obstacles under 1400 mm should not be used without additional safety-related measures, since these obstacles are too easy to climb over.

EN ISO 13854 crushing hazards overview

EN ISO 13854 specifies – depending on the part of a person's body concerned – minimum distances between two moving machine parts or one moving and one fixed machine part which are not considered to pose a significant crushing risk. If these distances can be maintained during design of a machine, then no further protective measures are necessary here with respect to crushing risks, and openings of this size can be considered as inherently safe.

Required minimum distances for access with:

If for design reasons these distances cannot be observed, additional technical measures such as guards and electro-sensitive protective devices must be used to prevent access or to ensure prompt shutdown of the hazardous movements. They fulfill their protective function only if they are mounted at a minimum distance away from the point of operation to be guarded.

If guards are used in accordance with EN ISO 13857, the following aspects must be taken into consideration when determining the fixed value for the safety distance:

• Opening sizes and penetration depths – safety distance depending on the part of the body concerned as given in a table
• Reach-over – height of the protective device depending on the distance and height of the point of operation as given in a table
• Crawl-under – gap below guards ≤ 180 mm