Feature Industrial compliance Standard stops danger in time
An analysis of the operation of a machine will identify movements which constitute elements of a hazard. These are the elements which could simply be expressed as constituting ‘clear and present danger’ to the operator. In the face of this danger to personnel there is no room for complacency says Sick safety specialist, Seb Strutt
Right: A reach over safety distance calculation is new to the standard
espite having one of the most comprehensive safety regimes in the world due to successive machinery safety legislation and associated technical standards in the EU, Strutt believes we can’t sit back and assume all is right.
D Safeguard positioning
The introduction of BS EN ISO 13855:2010 ‘Safety of machinery - positioning of safeguards with respect to the approach speeds of parts of the human body’, highlighted how machinery operators might put their safety at risk, without knowing it. Thus, it is vital a protective measure can react in time. Incorrect positioning of the safety device is one of the most common reasons for compliance fail- ure. Sick has observed this on count- less occasions during initial safety inspections, yet the provisions and implementation are simple and compliance can easily be achieved. The standard BS EN ISO 13855:2010 is an excellent step forward, and fills an important gap in the previous standard. What must be accurately measured, by a competent person, is the distance from the hazard point to the safety device and its orientation relative to the hazard. However, the precision required for complex safe distance calculations and the need for accuracy in estimating the safe stop time of the hazardous movement, is vital to achieving compliance.
Compliance with confidence Manufacturer derived safety distance calculation tools and stop time mea- surement services can remove the uncertainty from the required measure- ments, and establish the exact distances
26
needed for compliance. By taking advantage of these, or using measure- ment services, the engineer gains peace of mind and reduces the risk of acci- dent. Identifying the minimum safe dis- tance measurement is critical. This is why Sick offers a stop time calculation service prior to and following installa- tion of new safety measures.
Positioning preventive devices BS EN ISO 13855 applies to safety light curtains as well as other preventative measures such as pressure sensitive mats and two hand control systems. The standard is intended to ensure accessible hazards with mechanical movement are protected by an electro- sensitive protective device (ESPE). This device can detect an approach to the hazard and initiate a stop command which brings the mechanical motion to a safe condition.
Distance calculations
A good example is a typical hand-fed machine press. In the event that work is misplaced, a common operator response is to try and grab the item
A typical set up with a vertical light curtain, where the safety distance is shown as S
Sick UK
01727 831121
www.sick.com Enter 329
during the down stroke of the press. The operator’s hand speed could easily reach two metres a second. If the pro- tective light curtain is positioned too close to the press a hand could reach the hazardous zone before the press can react to the curtain’s stop command – the consequences could be devastating. For a vertical light curtain, the safety distance (safety reach through or Srt) is calculated from the speed of approach (K) multiplied by total response time of the machine (T) plus a constant (C) dependent on the specification of the light curtain, Srt = (K*T) + C. With a full body access detection multiple beam light guard (typically three or four beams), the equation becomes, Srt = (K * T) + 850mm. When using multi- ple beams, the minimum safety dis- tance should be greater than 850mm to accommodate the arm length when reaching through the light beam grid.
Hazardous reaching over The completely new element of the 2010 standards tackled the problem of operatives reaching over light cur- tains. The height of the hazard from ground level, when reaching from a standing position, is a major deciding factor in the height of the top beam of the light curtain.
The reach over safety distance (Sro) is calculated by adding a specially mea- sured constant (Cro) into the equation, Sro = (K*T) + Cro - (see diagram top). Cro is derived from the table above. Areas of the table marked ‘0’ show where the hazard cannot be accessed by overreaching. This means a hazard height of 800mm, with the upper edge of the light curtain detection zone at 1,600mm, cannot be accessed by overreaching. If the standard Srt safety distance is also calculated for the set- up, the resultant safety distance adopted should be whichever is greater – Srt or Sro. The results can be attached to the machine under scrutiny, as an immediate guide to its safe operation and safety status.
SEPTEMBER 2012 Factory Equipment
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56