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Preventing injuries on horizontal ladders and track rides

Preventing injuries on horizontal ladders and track rides
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  Abstract Objectives . This study examined the type of injury, fallheights and measures of impact attenuation of surfaces onwhich children fell from horizontal ladders and track rides.  Method  . All injured children who presented to two children’shospitals and received medical attention following a fall froma horizontal ladder or track ride in a public school or park during 1996–1997 were interviewed and the playground visited.  Results . The number of children who fell from horizontalladders and track rides and presented to hospitals with injurywas 118. Of those children, 105 were injured when they hitthe ground and data were available on 102 of those play-ground undersurfaces. Fractures to the arm or wrist were themost common injury.The median height fallen by children was 1930mm, 73%of injuries were from falls greater than 1800mm. In 41% of sites, the surface was deficient in impact absorbing proper-ties for the height of the equipment.Fractures were no more likely on loose surfaces than other surfaces, such as rubber matting (p = 0.556) but more preva-lent on compliant than non-compliant surfaces. Relative tofalls occurring on noncompliant surfaces, the odds of a frac-ture occurring on a compliant surface was 2.67 (95% CI0.88–8.14). Conclusions . Modification of the height of horizontal laddersand track rides to 1800mm is preferable to removal of such equipment. The prevalence of fractures on compliant surfaces suggests that the threshold of 200g or 1000 head injury criteria (HIC) needs to be revisited, or additional test criteria added to take account of change in momentumthat is not presently accounted for with either g-max on HICcalculations. Keywords: Children; playground equipment; horizontalladders and track rides; critical fall height; impact testing. Introduction Climbing equipment has been implicated in greater numbersof injured children between 5–9 years of age than any other type of playground equipment. 1,2 More recently, Mott et al. 3 have identified horizontal ladders as the climbing equipmentmost likely to produce an injury and recommended their removal. In 1999 Sibert et al. reported a reduction ininjury, following replacement of horizontal ladders withother equipment and increasing the depth of bark under equipment. 4 Chalmers, 5 Mott, 3 Briss, 6 and Mowat 7 have identified height of equipment, type and depth of surface, as key factorsin risk of injury to children from playground falls. In order to compare the effectiveness of different surfaces, an objec-tive measure is required. Standards in USA and Australia rec-ommend impact attenuation testing as evidence of surfaceattenuation properties. The properties of the surface deter-mine the height of equipment suitable for that surface. Testrequirements differ between countries and limited guidelinesare given for field testing. 8,9 We report the extent of injury, the heights of the equip-ment and the performance, measured by impact test equip-ment, of the surfaces impacted by the child. Based on theresults of our study, we recommend preventive options. Received 26 August 2003; In final form 15 December 2003. Correspondence : A/Professor Jim Nixon, Department of Paediatrics and Child Health, Royal Children’s Hospital, Herston, 4029, Australia.Tel.: + 617 3365 5322, E-mail: Preventing injuries on horizontal ladders and track rides James W. Nixon 1,5 , Caroline H.C. Acton 1 , Belinda A. Wallis 1 , Diana Battistutta 2 , Clare Perry 3 and David B.M. Eager  41 Department of Paediatrics and Child Health, University of Queensland, Australia, 2 School of Public Health, Queensland University of Technology, Australia, 3 Ipswich Hospital, Ipswich, UK, 4 Mechatronics and Intelligent Systems, Faculty of Engineering, University of Technology, Sydney, Australia, 5 Visiting Fellow National Injury Prevention Center, Centers for Disease Control and Prevention Atlanta, USA Injury Control and Safety Promotion2004, Vol. 11, No. 4, pp. 219–224DOI: 10.1080/156609704/233/289733© 2004 Taylor & Francis Ltd.  220J.W. Nixon et al. Method The study was conducted between 1 January 1996 and 31December 1997 inclusive. Children were included in thestudy if they fell, were pushed or jumped from a horizontalladder or track ride (fixed track flying fox) in a public park or public school in the city of Brisbane and attended either of the two public children’s hospitals.Horizontal ladders and track rides are specificallydesigned to exercise the upper body and both require similar  physical skills. For this reason both types of equipment have been included in this study. The majority of injuries on both pieces of equipment are from arm fractures. 3 Questionnaireswere completed in the emergency department by consenting parents or carers. Site visits were made and data were col-lected at the playground. Type of equipment, location withinthe playground (where there was more than one of that equip-ment), type of surface fallen to, height of equipment, descrip-tion of the circumstances of the incident and the mechanismof injury were recorded. Medical records provided details of the injury and the weight of the child as recorded on pre-sentation to hospital. Z-scores, comparing children in thissample to American normalized data 10 were calculated for weight for age of the children. Normal data of weight for agefor Australian children are not available. We have used, con-ventionally, the 85th percentile of weight for age to definelarge children. 11 A visit was made to the playgrounds in public parks and  public schools, where possible within 4 days of the injury.Heights of equipment were measured and details of the typeand depth of under-surfacing material were recorded. Heightwas measured from the surface under the equipment to therungs of the horizontal ladder and, in the case of track rides,from the surface under the equipment to the glide handle held  by the child during the ride. It was clear from interviews withchildren that some fell from holding the rungs while some had been climbing on top of the horizontal ladder.Attempts to determine the height were abandoned because of discrepancies between interview data and measurements atthe site. The majority of falls were not witnessed and corrob-oration was not possible. In those cases where the event waswitnessed, parents tended to overestimate the distance fallen.The impact attenuation measure for equipment undersur-faces was determined using a commercially available testing unit with an accelerometer mounted in a 5.4kg (12lb) hemi-spherical headform attached to a handheld com- puter from Playground Clearing House, USA. Four peoplewere trained in the use of the testing equipment using Play-ground Clearing House material and the Australian standard for testing surfaces. 9 Each site was visited by two of thetrained people.The measure of g-max and HIC values was determined from four drops, at each of four locations at the corners of a500mm square, on the fall zone beneath the equipment. Thereliability and validity of the results of similar testing have been questioned following recent laboratory based tests. 12 However, impact attenuation remains the recommended method in USA, Canada and Australia through the respec-tive standards associations. 7,8,13 Testing in this study wasundertaken in field conditions where variation in test samplescould be expected to be greater than in laboratory conditions.Impact testing was undertaken to determine if a fall from the height of the horizontal ladder or track ride would generate a value greater than 200g or 1000HIC. This thresh-old indicates the impact-absorption qualities of the surface.A nexus should exist between the height of the play equip-ment and the ability of the surface beneath the equipment toreduce and dissipate the impact energy of a fall from thatheight. The impact attenuation measure of the surface should determine the height of equipment placed over that surfaceor, conversely, if equipment is already in place, the fall heightfor the particular equipment should determine the mechani-cal properties and/or depth of the surface.Measurements were taken at heights less than, the sameand greater than the equipment height, where the gantryheight of 2400mm allowed. If a measurement of greater than 200g or greater than 1000HIC was achieved in any one of the 16 drops below the equipment height, the surfacewas considered to be non-compliant. 8 The surface wasdeemed to comply if the threshold values specified inAS/NZS4422:1996 could not be achieved at heights abovethe equipment height or the maximum test height possiblefrom the gantry. 9 Calibration was undertaken before and after testing in accordance with the measurement equipment supplier’s guideline.Head injury or concussion was defined as any loss of con-sciousness or lack of memory of the event, determined bythe attending emergency department physician and recorded in the medical record.Fall height was measured vertically from the top of thehorizontal ladder of the monkey bar, or the glide handle of the track ride, to the playground surface beneath. Depth of loose fill undersurfacing material was measured in mm, after removing the imported loose material with a spade until thenatural sub-grade was exposed.Data were entered on an Excel spreadsheet and tables gen-erated using SAS. 14 Calculation of injury and hospitalizationrates due to horizontal ladders and track rides were based onthe Brisbane population aged 0 to 14 years in the censusyear. 15 Regular visits to the emergency departments, computer-ized registrations, enrolment at registration and cross-checking against injuries were undertaken to ensure full casefinding in the public hospital sector. Our best estimate is that90% of all children injured on play equipment in Brisbaneand requiring hospital treatment were ascertained. Data onthe distribution of surface types were obtained from obser-vations in playgrounds in 16 parks and 16 schools randomlyselected from the city of Brisbane. 16 Approval to undertake this study was obtained from theRoyal Children’s Hospital Ethics Committee and the Mater Children’s Hospital Ethics Committee.  Preventing injuries on horizontal ladders and track rides221 Results Following injury on horizontal ladders and track rides, 118children attended emergency departments; 96 were injured on horizontal ladders and 22 on track rides. Together theseconstituted 48% of the 247 children injured on all play equip-ment in parks and schools in the same period.Fractures accounted for 69% and 68% of injuries on hor-izontal ladders and track rides respectively. More girls than boys were injured on horizontal ladders (57%) and more boysthan girls were injured on track rides (82%). Upper extrem-ity injuries (wrists, forearms, elbows) accounted for 79% of all injuries requiring medical attention (82% horizontalladders and 64% of track rides).Twenty children received more than one injury at the timeof the incident. None of the children in this study suffered concussion. Eighty-one children (69%) fractured bones and ten of these children each had two fractures. The mostcommon fracture among the 81 children who fractured boneswas to the wrist (48%) followed by the forearm (35%), elbow(7%) and upper arm (5%). Twelve children received injuriesto the face. Facial injuries included nasal fractures, dislodged teeth, lacerations, cuts, bruises and abrasions.Thirty-four (29%) of 118 children injured on horizontalladders and track rides were above the 85th percentile for weight for age.Eleven children’s injuries resulted from contact with theequipment. Seven of these children had injuries to the face,including one with a fractured nose, another with dislodged teeth and one sustained a forearm fracture. One child wasinjured in contact with another child while on the equipment.Data on contact were unavailable for one child. Children injured following contact with the ground (n = 105) Of the 118 children, 105 (89%) were injured as a result of impact with the ground. Of these children, 5% received facialinjuries, while 64% of those whose injuries followed contactwith equipment had injuries to the face. Surfaces onto which children fell when they hit theground (n = 102) The median height of the equipment was 1930mm with aminimum of 1500mm and a maximum of 2400mm; 73% of injuries were from falls greater than 1800mm. Almost 79%had some form of surface other than natural dirt or grassunder the equipment.Table 1 shows fractures and other injuries on each of four different surfacetypes, including grass or dirt, sand, bark and manufactured rubber surfaces. Surface types present under the equipment included bark 47 (46.2%), sand 14 (13.8%),rubber matting 19 (18.5%). Dirt or grass was the surfaceunder 22 (21.5%) of equipment.We considered whether equipment was installed on anappropriately safe surface for equipment of that height. Mea-sured data on impact attenuation were available for 102 of the 105 sites (Table 1) where injury had occurred due tocontact with the ground. Fifty-nine (57.8%) sites were found to be compliant (adequate in impact absorbing properties for the height of the equipment). Sufficient impact attenuation properties for the height of the equipment was found in 41%of dirt and grass surfaces, 50% of sand surfaces, 87% of bark surfaces and 16% of rubber-matting surfaces.Although large odds ratios were suggestive of an associa-tion between surface type and prevalence of fractures, statis-tically there was little support for an association between prevalence of and surface type (p = 0.556). However, for completeness, compared to dirt and grass, the relative oddsof fracture was 2.43-fold (95% CI 0.50–11.63) higher for sand, 2.17 (0.61–7.67) higher for bark and 1.92 (0.50–7.35)higher for rubber matting. Fractures were more prevalent oncomplying surfaces than non-complying surfaces. Adjusted for surface type and relative to non-compliant surfaces, theodds of a fracture on a compliant surface was 2.67 (95% CI0.88–8.14). On 61 of the play sites where sand or bark (loosematerial) was used for impact attenuation, the mean depth of the sand was 123mm (5–300mm range) and bark was 86mm(5–280mm range). The minimum depth of rubber mattingwas 20mm and the maximum 40mm. Table 1. Injury type, surface type and measured compliance of surface for 102 childreninjured on horizontal ladders and track rides in the city of Brisbane.Surface TypeFractureOther InjuryTotalDirt and grass Compliant  639 (8.8%)  Non Compliant  7613 (12.7%)Sand  Compliant  617 (6.9%)  Non Compliant  527 (6.9%)Bark  Compliant  36541 (40.3%)  Non Compliant  336 (5.9%)Rubber matting Compliant  213 (2.9%)  Non Compliant  11516 (15.6%)Total7626102 (100.0%)  222J.W. Nixon et al.Table 2 shows the distribution of the surfaces under hor-izontal ladders from an observation study in parks and publicschool playgrounds across the city of Brisbane. Childrenwere more likely to be injured on a rubber-matting surfaceand less likely to be injured on sand.Table 3 shows the numbers of children who fell on com- pliant and non-compliant surfaces from different heights. Of the injured children, 81% fell greater than 1800mm. A heightof 1800mm would allow a 9-year-old on the 97th percentilefor height with extended arms to clear the ground. Themedian equipment height was 1930mm and the modal equip-ment height 2000mm.The proportion of compliant surfaces decreased with theincreasing height of equipment (p = 0.001); 95% of equip-ment between 1500 and 1799mm was compliant, 56% of equipment between 1800 and 1999mm was compliant, compared to 43% of equipment of 2000mm or more beingcompliant. Discussion Unlike most other injury scenarios more girls than boys wereinjured on horizontal ladders. However, more boys than girlswere injured on track rides. The range of equipment heightswas from 1500mm to 2400mm. We used the height of thehorizontal ladder as the height from which the child fell, asthere were difficulties in obtaining an accurate measurementof the true distance fallen. Some children fell from a posi-tion standing on top of the monkey bar, while others fellwhilst brachiating or swinging from bar to bar. The highest piece of upper body equipment recorded was 2400mm. Inthis study, 81% of children were injured on horizontal laddersand track rides greater than 1800mm, with the modal fallheight being 2000mm.The heights of most horizontal ladders and track ridesmeasured were considered to be greater than necessary for effective use. Chalmers et al. have suggested a safe heightfor playground equipment of 1500mm, and 1600mm for climbing frames 5 however, these heights are not practicalwhen applied to horizontal ladders and track rides. A child of 9 years (the eldest of the group most at risk) on the 95th percentile is approximately 1700mm with an extended upper arm. 17 To enable a child to effectively use a horizontal ladder,we suggest 1800mm as an effective height.Of 118 injured children, 29% were considered to be largechildren (that is, above the 85th percentile of weight for age).Although these children were over-represented in falls fromthe horizontal ladders or track rides, they were no more likelyto fracture bones and the pattern of injury was no differentfrom their smaller peers (data not shown).All of the loose materials tested in the laboratory byBullen and Jambunathan 18 gave a safe fall height of greater than 3000mm at 200mm depth even in a wet, compacted condition. Mack et al., 12 after testing five different materialsin laboratory conditions, found better results on compressed rather than uncompressed loose surfaces. They indicated thatfor loose-fill materials, impact testing could produce unreli-able results under some circumstances. In this study, intesting done in field conditions, we found that in 41% of cases, where children fell to the ground, the measured surfacewas inadequate for the height of the equipment installed. Itshould be noted that 83% of children who fell to a play-ground surface that complied technically with the g-max and HIC threshold measures sustained a fracture.The Australian, US and Canadian standards have been produced specifically to prevent serious head injury. No chil-dren in this study suffered head injury from falling fromupper body equipment. As 58% of the surfaces complied for impact attenuation properties, the lack of head injuries may be associated with the manner in which children fell fromthis single style of equipment rather than the surface itself.Studies from Mott 3 and Laforest 19 suggest that the currentrecommendations of 300mm bark loose fill depth or 200g/1000HIC have reduced head injury but are inadequate to prevent limb fractures. They should be reviewed as further data become available on biomechanics, surface attenuation properties and fall heights. 20  Neither the 200g nor the 1000HIC criteria that are called up in all the major undersurfacing test methods 7,8,13,21 takeaccount of the impact force associated with bounce. We con-sider change in momentum may also contribute to fractureswhere 200g or 1000HIC is not achieved on playground undersurfacing. Table 2. The number of children injured on particular surfaces and the proportion of different surfaces from our sample of playgroundsin Brisbane parks and public schools.Surfaces in BrisbaneTotal Injured onSurface TypeSample (%)Each SurfaceDirt and grass2222 (21.7%)Sand3014 (13.7%)Bark4847 (46%)Rubber matting  < 119 (18.6%)Total100102 Table 3.  Number of injured children on equipment of variousheights and whether the surface fallen to was compliant at < 200gor < 1000 head injury criteria.EquipmentCompliantNon-CompliantHeightSurfaceSurfaceTotal < 1500mm0001500–  < 1800mm18 (94.7%)1(5.3%)19 (100%)1800–  < 2000mm22 (56.4%)17 (43.6%)39 (100%) > 2000mm19 (43.2%)25 (56.8%)44 (100%)Total5943102  Preventing injuries on horizontal ladders and track rides223Although horizontal ladders and track rides produce moreinjuries than any other piece of equipment, 3 they are the most popular in the playground. We have found in observationsthat horizontal ladders were used 2.6 times and 7.8 timesmore often than other climbing equipment, in schools and  parks respectively. 16 Of all the surfaces under horizontalladders, a greater proportion than expected were injured onrubber matting and a lesser proportion of injuries occurred on sand regardless of whether those surfaces complied withimpact testing. Limitations Accuracy of fall height was difficult to determine. Childrenfell from standing on the equipment or hanging from theequipment by their arms. We have assumed that fall heightwas equal to the equipment height. As it was not possible todetermine the fall height accurately for every child, this mayhave affected the surface compliance results for those chil-dren who fell from the top of the equipment. Further, the useof the accelerometer testing in field conditions using themethod described in the Australian standard proved difficult.Had the Australian standard been followed absolutely, 50%of the data would have been discarded. The method used inthis study for the selection and analysis of drop data was amodification of the Australian and US standards. Case selec-tion was limited to children attending public hospitals, whichwe estimate to be 90% of all children injured. Conclusions Horizontal ladders and track rides are associated with themajority of bony fractures occurring from playground equip-ment. We argue that modification of the height of this popular equipment to 1800mm is only one possible solution to the problem. In our view modification is preferable to removalof such equipment. The finding that so many fracturesoccurred on surfaces complying with HIC and g-max mea-sures suggests that while the thresholds for compliancereduce head injury they are too high to reduce long bone fractures. Implications for prevention •Biggest potential gains in preventing playground fallinjuries are from focus on horizontal ladders and track rides and the surfaces under them.•It is recommended that 1800mm is a compromise heightfor horizontal ladders and track rides. Horizontal ladder and track ride equipment height needs to be greater than1500mm to allow effective use and less than 2000mm toreduce injury.•Findings about surface materials tested in the field, whenassociated with the fracture injuries occurring, suggest thethreshold of 1000HIC and 200g-max needs to be recon-sidered, or additional test criteria added to take account of change in momentum associated with bounce, not presently accounted for with either the g-max or HIC calculation.•Detailed data on fall height and biomechanics of injuryassociated with falls from this type of equipment is needed. Acknowledgements This research is a project of Injury Prevention and ControlAustralia Ltd. supported by grants from South East Queens-land Regional Organization of Councils (SEQROC), Education Queensland and the NHMRC. We acknowledgethe cooperation of The Queensland Injury Surveillance Unit, Brisbane City Council and the Emergency Departmentsof the Royal Children’s Hospital and the Mater Children’sHospital. References 1Lillis KA, Jaffe DM. Playground injuries in children.  Pediatr  Emerg Care . 1997;13(2):149–153.2Briss PA, Sacks JJ, Addiss DG, Kresnow M, O’Neil JA. Nationwide study of the risk of injury associated with daycare center attendance.  Pediatrics . 1994;93(3):364–368.3Mott A, Rolfe K, James R, Evans R, Kemp A, Dunstan F, etal. Safety of surfaces and equipment for children in play-grounds.  Lancet  . 1997;349(9069):1874–1876.4Sibert J, Mott A, Rolfe K, James R, Evans R, Kemp A, et al.Preventing injuries in public playgrounds through partner-ship between health services and local authority: communityintervention study.  BMJ  . 1999;18(12 June):1595.5Chalmers DJ, Marshall SW, Langley JD, Evans MJ, BruntonCR, Kelly AM, Pickering AF. Height and surfacing as risk factors for injury in falls from playground equipment: Acase-control study.  Inj Prev . New Zealand. 1996;2:98–104.6Briss PA, Sacks JJ, Addiss DG, Kresnow MJ, O’Neil J.Injuries from falls on playgrounds. Effects of day care center regulation and enforcement.  Arch Pediatr Adolesc Med  .1995;149(8):906–911.7Mowatt DL, Wang F, Pickett W, Brison RJ. A case-controlstudy of risk factors for playground injuries among childrenin Kingston and area.  Inj Prev . 1998;4(1):39–43.8American Society for Testing Materials.  ASTM F1292–99.Standard Specification for Impact Attenuation of SurfaceSystems Under and Around Playground Equipment  . ASTMInternational, West Conshohocken, PA, 1995.9Standards Australia.  AS/NZS 4422:1996 Playground Sur- facing – Specification, Requirements and Test Method  . Standards Australia: Sydney, 1996.10Centers for Disease Control. Anthro Software for calculat-ing Pediatric Anthropometry. 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