437-007-0660 Intermediate Support Trees (1) Intermediate support trees must be rigged so: (a) Horizontal carriage clearance at the base of the intermediate support tree(s) is sufficient for the turn of logs to pass the support tree(s). (b) The jackline is a single piece of line that provides strength equal to a line 1/8-inch larger than the tong or skidding line. (Figures 7-17, 7-19 and 7-20.) Extensions may be attached to the anchor end of the jack-line. (2) Vertical support trees must be firmly rooted. (3) The base of all leaning tree supports must be prevented from moving by: (a) Retaining 20 percent of the stump diameter in holding wood; or (b) Other suitable rigging arrangements. (4) Single tree intermediate supports must be guyed as follows: (a) For skylines 1-inch and smaller use the rigging configuration in Figure 7-17: (A) No guylines are required when at the point of rigging attachment the tree does not move more than its diameter in the direction of load as shown in Figure 7-18. (B) If the tree moves more than one diameter at the point of rigging attachment, then a guyline of the size called for in 437-007-0650(4) must be rigged to oppose the yarding forces. Figure 7-18 — Tail and Intermediate Support Tree Stability [Figure not included. See ED. NOTE.] (b) For all skylines larger than 1-inch and for skylines rigged as in Figure 7-17. (A) Two guylines are needed of the sizes called for in 437-007-0650(4)(c). (B) The guylines must be rigged according to 437-007-0655(4) if the tree is not stable according to Figure 7-18. (c) For all leaning tree intermediate supports using the rigging configuration of Figure 7-19, a minimum of three guylines must be used. (A) Two guylines of the sizes called for in 437-007-0650(4)(c) must be rigged according to Appendix 7-I, Figure 7-42. (B) A snap guyline of at least 3/8-inch diameter must be placed opposite the two load-bearing guylines. Figure 7-19 — Intermediate Support Tree — Leaning [Figure not included. See ED. NOTE.] (5) Double tree supports must be rigged (see Figure 7-20) so the: (a) Angle of the block to the center of the support line: (A) Is 10 degrees in any direction when skylines 1 1/8-inch and smaller are used; or (B) Has deflection in the direction of the jack which does not exceed 10 degrees when skylines larger than 1 1/8-inch are used. (b) Loaded support trees do not displace more than 2 feet at the point of rigging attachment. (c) Minimum and maximum heights of the jack relative to the height of the block is as shown below for double tree intermediate support systems. Figure 7-20 — Intermediate Support — Double Tree [Figure not included. See ED. NOTE.] (6) Double tree supports must be guyed as follows: (a) For skyline sizes equivalent to 1 1/8-inch improved plow steel (IPS) and less, no guys are required; (b) For skyline sizes equivalent to those larger than 1 1/8-inch IPS as shown in Appendix 7-I, Figure 7-39. [ED. NOTE: Figures and Appendices referenced are available from the agency.] Statutory/Other Authority: ORS 654.025(2) & 656.726(4) Statutes/Other Implemented: ORS 654.001 - 654.295 History: OSHA 2-2005, f. 5-27-05, cert. ef. 6-1-05 OSHA 3-2004, f. & cert. ef. 6-7-04 OSHA 5-2003, f. 6-2-03, cert. ef. 12-1-03