Protective devices with 3D safety zones on machinery: review of access by crawling

Project No. IFA 5125


completed 01/2014


Electro-sensitive protective equipment (ESPE) detects the position of a person and thus ensures that an adequate safety clearance is maintained to danger zones on machinery. ESPE with three-dimensional safety zones, for example modern camera systems with optical depth measurement, is used for example to safeguard collaborative industrial robots. The principle of these systems requires a minimum clearance to be observed to perimeter surfaces such as walls or floors, in order for false positives caused by measurement error to be excluded. EN ISO 13855 "Safety of machinery – Positioning of safeguards with respect to the approach speeds of parts of the human body" specifies a minimum height of the lower beam of 30 cm above the ground for ESPE with a two-dimensional safety zone, such as light curtains and light barriers, in order to prevent undetected crawling beneath the safety zone. No special normative provisions exist at present for three-dimensional safety zones. Since, in this case, a person must crawl beneath a two-dimensional plane rather than a single light beam, it was to be determined whether the minimum height of three-dimensional safety zones above the ground could be increased, for example to 40 or 50 cm. Amendment of the standard could facilitate the introduction of ESPE with three-dimensional safety zones to the market. This equipment would enable danger zones on machinery to be monitored that before now could not be adequately safeguarded.


Undetected crawling beneath two-dimensional planes was studied systematically with a random sample of 43 test subjects. EN ISO 13855 assumes that persons in an industrial environment are at least 14 years of age. The study was therefore performed with two classes of schoolchildren. The children's relevant body dimensions were also measured, and their fitness levels determined by means of a questionnaire. Pilot studies were performed with ten members of the IFA's staff in order to optimize the test arrangement. A laser scanner was selected for monitoring and logging violations of the safety zone. The studies were performed at mechanically variable heights of between 20 and 50 cm. The dimension of the safety zone below which test subjects were to crawl was switched between 20 cm and 2 m in order to examine different crawling techniques. Test subjects crawled adjacent to each other in groups of three. Each test subject received personal visual and acoustic feedback of their violations of the safety zone. The crawling speed was recorded simultaneously. A second test setup studied passing of a safety zone to the side along a wall. Suitably modified tests were performed for this purpose with the ten IFA staff members.


The selected test arrangement enabled the study task to be performed systematically. The horizontal measurement error was ±15 mm. The children's body dimensions were within the normal statistical range. The children were motivated; a discernible contributory factor in this respect was the competitive aspect. Almost all test subjects were able to crawl undetected beneath a safety zone at a height of 30 cm. The majority of the children and some of the adults also managed to pass a zone at a height of 25 cm. A safety zone with a height of 20 cm was passed undetected by only a single child test subject. The estimated maximum crawl speed is 0.4 m/s. Physical stature had an effect upon the crawl performance and speed. Fitness had an effect more upon the speed. The clearances between the fixed perimeter and the invisible envelope of the safety field that could be passed undetected in the tests of passing to the side exhibited similar values to those in the crawl tests. The speed for passing to the side was however estimated as being higher, with a maximum of 0.6 m/s.

The results of the study do not therefore justify an increase in the required minimum height above the ground of three-dimensional safety zones to a value higher than the present value of 30 cm.

The results of the study were published on an information sheet (PDF, 470 KB) issued by the Woodworking and metalworking expert committee, and are to be introduced into the relevant standardization work (such as that for DIN EN ISO 13855).

Last Update:

24 Apr 2014


Financed by:
  • Deutsche Gesetzliche Unfallversicherung e. V. (DGUV)
Research institution(s):
  • Institut für Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung (IFA)
  • Berufsgenossenschaft Holz und Metall (BGHM)
  • Prüf- und Zertifizierungsstelle Hebezeuge, Sicherheitskomponenten und Maschinen

-cross sectoral-

Type of hazard:

mechanical hazards


machine safety, man-machine interface, technical protective measures (exposure reduction/ protective devices)

Description, key words:

crawling zone, access beneath or to rear of safety zones, safety distances, electro-sensitive protective equipment (ESPE), non-contact, protective devices, machines, danger zones, detection zone, safety zone, camera system, work zone, approach, position, velocity, resolution, usability, ergonomics, manipulation, robots, laser scanners, circumventing, access