Confined Space Retrieval Winch Force

The free-hanging case is straightforward arithmetic and it is the easy half of the problem. AN ENTANGLED OR WEDGED ENTRANT IS A DIFFERENT NUMBER ENTIRELY. The force required can be several times body weight, and a system sized for the free-hanging case stalls at it -- which is the moment the retrieval was supposed to handle. Sizing to the free-hanging load alone produces equipment that works in the drill and not in the event. THE SYSTEM IS RATED AS A SYSTEM AND THE RATING IS ITS WEAKEST ELEMENT. Winch, line, davit or tripod, and anchorage: a winch rated well above the load, mounted on a tripod whose footing is inadequate, is a system rated by the footing. Reading the winch's nameplate as the system's capacity is how a rated-looking arrangement fails, and the anchorage is the element least often calculated because it is usually the structure that happened to be there. AND THE UPPER LIMIT IS MEDICAL RATHER THAN MECHANICAL, which is the part that makes this different from a rigging calculation. Pulling hard enough to free a wedged entrant can injure them badly. A retrieval that does not come freely is a signal to STOP and move to the entry rescue plan -- so that plan has to exist, with a trained and equipped team able to reach the space in time, even where retrieval equipment is provided. Retrieval is not always feasible: some space configurations do not permit it, and where they do not, an entry rescue capability is required rather than optional. THE REASON THE WHOLE ARRANGEMENT EXISTS is that most confined space fatalities include would-be rescuers, who entered without protection to help someone who had collapsed and were overcome by the same atmosphere. Non-entry retrieval is what breaks that pattern, and its details carry the outcome: the harness attachment above the entrant's centre of gravity so they come out vertically rather than jamming, the line kept taut so there is no slack, and the winch positioned so the pull is in line with the opening. This computes a force from entered weights and allowances. It does not size or select a retrieval system, winch, harness or anchorage, evaluate an anchorage's actual capacity or its attachment, determine whether non-entry retrieval is feasible for a given space, assess the atmosphere or any other hazard in the space, write an entry permit or a rescue plan, or evaluate rescue team capability and response time. 29 CFR 1910.146, ANSI Z117.1, the equipment manufacturer's ratings, and the entry supervisor govern.

retrieval force = (entrant + equipment weight) x (1 + friction allowance), with an entanglement factor applied separately; the system rating is the MINIMUM of the winch and the anchorage.

Confined space non-entry retrieval as 29 CFR 1910.146 and ANSI Z117.1 require it. The friction allowance (commonly about 15%) and any entanglement factor are ENTERED, because both depend on the space and the configuration.

One sum and one comparison against entered ratings.

Estimate. AHJ and licensed professional govern.

Field names used by the API: entrant_weight_lb, equipment_weight_lb, friction_pct, entanglement_factor, system_rating_lb, anchorage_rating_lb, suspended_lb, friction_lb, retrieval_lb, entangled_lb, system_margin_lb, anchorage_margin_lb, weakest_rating_lb

• Friction and entanglement are entered both depend on the space and configurationthe entry supervisor
• Rated as a system the weakest element governs, and the anchorage is least often calculatedthe equipment manufacturer's ratings
• Feasibility is not determined some configurations do not permit non-entry retrieval at all29 CFR 1910.146 and the rescue plan