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I manichini da crash test hanno salvato diverse migliaia di vite!

I manichini da crash test sono delle riproduzioni in scala di esseri umani, con il giusto peso e le articolazioni per simulare il comportamento di un corpo umano, e dotato di strumentazioni per registrare il maggior numero di dati possibili sulle variabili di un incidente, come la velocità d'urto, le forze di schiacciamento, di piegamento, o di torsione del corpo e la decelerazione al momento della collisione. Anche al giorno d'oggi essi restano indispensabili nello sviluppo di nuovi modelli per ogni tipo di veicoli, da una berlina a un caccia.

[modifica] La necessità dei test

Il 31 agosto 1869, Mary Ward fu la prima vittima registrata di un incidente automobilistico, a Parsonstown in Irlanda. ^[1] Alcuni anni più tardi, il 13 settembre 1899, Henry Bliss "passò alla storia" come la prima vittima di un incidente automobilistico nel nordamerica, dopo che fu investito mentre scendeva da un tram a New York. Da quel giorno, oltre 20 milioni di persone in tutto il mondo hanno perso la vita a causa di incidenti automobilistici.

Il bisogno di un mezzo per analizzare e attenuare gli effetti degli incidenti stradali sul corpo umano si sviluppò rapidamente subito dopo la commercializzazione dell'automobile (intorno al 1890) e quando l'auto diventò significativa nella vita quotidiana, verso il 1930, il numero di morti per incidente stava raggiungendo una quota preoccupante. I tassi di mortalità superarono i 15,6 incidenti ogni 100 milioni di miglia per veicolo e continuavano a crescere; i progettisti di veicoli interpretarono questi dati come una chiara indicazione della necessità di fare delle ricerche per rendere più sicuri i loro prodotti.

Nel 1930, l'interno di un'auto non era un luogo sicuro neanche in caso di collisione a velocità ridotta. I cruscotti erano costituiti da metallo rigido, il piantone dello sterzo non era pieghevole e ovunque vi erano pomelli, pulsanti e leve sporgenti. Non si conoscevano le cinture di sicurezza e in un impatto frontale gli occupanti venivano scagliati contro il parabrezza, lasciando poche speranze di evitare gravi ferite o di morire. La struttura stessa del veicolo era rigida, e le forze d'urto erano trasmesse direttamente agli occupanti del veicolo. Negli anni '50 i fabbricanti di automobili dichiararono pubblicamente che non si poteva rendere meno dannosi gli incidenti, poiché le forze in uno scontro erano troppo grandi e il corpo umano troppo fragile.

[modifica] Test sui cadaveri

La Wayne State University di Detroit fu la prima a iniziare un intenso lavoro di raccolta di dati riguardo agli effetti sul corpo umano degli scontri a velocità elevata. Sul finire degli anni '30 non vi erano però risultati affidabili sulle risposte del corpo umano sottoposto ad estreme sollecitazioni fisiche, e non vi erano nemmeno strumenti adatti a misurare tali risposte. La biomeccanica era un campo della scienza ancora allo stadio iniziale. Era quindi necessario utilizzare diversi soggetti per costruire i primi set di dati.

I primi soggetti per i test furono dei cadaveri umani. Essi erano usati per ottenere informazioni fondamentali circa la capacità del corpo umano di resistere alle forze di schiacciamento e di strappo che si verificavano solitamente in incidenti ad alte velocità. Per finalità simili, si facevano cadere dei cuscinetti a sfera di acciaio sul cranio, oppure si lanciavano i corpi giù nei pozzi degli ascensori inutilizzati contro lastre di acciaio. Inoltre cadaveri con rudimentali accelerometri venivano legati all'interno delle automobli e sottoposti a collisioni frontali e a rollover.

In un articolo del 1995 pubblicato sul Journal of Trauma, dal titolo "Humanitarian Benefits of Cadaver Research on Injury Prevention" (Beneficî umanitari della ricerca con i cadaveri sulla prevenzione degli infortuni), Albert King dichiara chiaramente il numero di vite umane salvate grazie alla ricerca sui cadaveri. I calcoli di King indicano che grazie ai cambiamenti dei progetti attuati fino al 1987, la ricerca sui cadaveri ha salvato 8500 vite all'anno. Evidenzia inoltre che per ogni cadavere usato ogni anno 61 persone si sono salvate per aver indossato la cintura di sicurezza, 147 grazie all'air bag, e 68 sono sopravvissuti all'impatto con il parabrezza.^[2]

Ad ogni modo lavorare con i cadaveri presentava tanti problemi quanti ne risolveva. Non c'erao solo le questioni morali ed etiche relative al lavoro con i morti, ma anche i problemi di ricerca. La maggior parte dei cadaveri disponibili erano adulti anziani e di razza caucasica, che erano morti per cause non violente; essi non rappresentavano una parte omogenea delle vittime per incidente. Le vittime per incidente però non potevano essere utilizzate poiché ogni dato raccolto con gli esperimenti poteva essere compromesso dalle precedenti ferite del cadavere. Dal momento che poi nemmeno due cadaveri sono identici, e siccome ogni singola parte di un cadavere poteva essere usata una sola volta, era particolarmente difficile ottenere affidabili dati di confronto. Inoltre nel caso dei cadaveri di bambini, non solo essi erano difficili da ottenere, ma sia l'opinione pubblica che la legge rendevano il loro uso impraticabile. Infine, man mano che i crash test andavano intensificandosi, i cadaveri adatti diventavano sempre più scarsi. Di conseguenza i dati biometrici erano limitati al "maschio anziano bianco".

[modifica] Test sui volontari

Alcuni ricercatori si incaricarono di fare da manichini per i crash test. Il colonnello USAF John Paul Stapp si lanciò a più di 1010 km/h (630 mph) su una slitta a razzo (rocket sled) e si è fermò in meno di 1 secondo. ^[3] Lawrence Patrick, un professore della Wayne State University ora in pensione, si sottopose a circa 400 corse sulla slitta a razzo con lo scopo di verificare gli effetti di una rapida decelerazione sul corpo umano. Lui e i suoi studenti si fecero schiantare sul petto con un pendolo di metallo, si fecero urtare sul viso da un martello pneumatico rotante ed infine schizzare con vetri frantumati per simulare l'implosione di un finestrino. ^[4] Nell'ammettere che questo gli procurava "un piccolo dolore", Patrick affermò che la ricerca condotta da lui e dai suoi studenti poneva le basi per lo sviluppo di modelli matematici con cui la ricerca futura avrebbe potuto confrontarsi. Ma benché i dati derivanti dai test sui viventi fossero attendibili, le cavie umane non potevano di certo sopportare prove che superassero un determinato grado di stress fisico. Per raccogliere informazioni sulle cause e sulla prevenzione degli infortuni c'era bisogno di un altro tipo di soggetto.

[modifica] Animal testing

By the mid-1950s, the bulk of the information cadaver testing could provide had been harvested. It was also necessary to collect data on accident survivability, research for which cadavers were woefully inadequate. In concert with the shortage of cadavers, this need forced researchers to seek other models. A description by Mary Roach of the Eighth Stapp Car Crash and Field Demonstration Conference shows the direction in which research had begun to move. "We saw chimpanzees riding rocket sleds, a bear on an impact swing...We observed a pig, anesthetized and placed in a sitting position on the swing in the harness, crashed into a deep-dish steering wheel at about 10 mph."^[5]

One important research objective which could not be achieved with either cadavers or live humans was a means of reducing the injuries caused by impalement on the steering column. By 1964, over a million fatalities resulting from steering wheel impact had been recorded, a significant percentage of all fatalities; the introduction by General Motors in the early 1960s of the collapsible steering column cut the risk of steering-wheel death by fifty percent. The most commonly used animal subjects in cabin-collision studies were pigs, primarily because their internal structure is similar to a human's. Pigs can also be placed in a vehicle in a good approximation of a seated human.

The ability to sit upright was an important requirement for test animals in order that another common fatal injury among human victims, decapitation, could be studied. As well, it was important for researchers to be able to determine to what extent cabin design needed to be modified to ensure optimal survival circumstances. For instance, a dashboard with too little padding or padding which was too stiff or too soft would not significantly reduce head injury over a dash with no padding at all. While knobs, levers, and buttons are essential in the operation of a vehicle, which design modifications would best ensure that these elements did not tear or puncture victims in a crash? Rear-view mirror impact is a significant occurrence in a frontal collision; how should a mirror be built so that it is both rigid enough to perform its task and yet of low injury risk if struck?

While work with cadavers had aroused some opposition, primarily from religious institutions, it was grudgingly accepted because the dead, being dead, felt no pain, and the indignity of their situations was directly related to easing the pain of the living. Animal research, on the other hand, aroused much greater passion. Animal rights groups such as the ASPCA were vehement in their protest, and while researchers such as Patrick supported animal testing because of its ability to produce reliable, applicable data, there was nonetheless a strong ethical unease about this process.

Although animal test data were still more easily obtained than cadaver data, the fact that animals were not people and the difficulty of employing adequate internal instrumentation limited their usefulness. Animal testing is no longer practiced by any of the major automobile makers; General Motors discontinued live testing in 1993 and other manufacturers followed suit shortly thereafter.

[modifica] Dummy evolution

Sierra Sam tested ejection seats.

The information gleaned from cadaver research and animal studies had already been put to some use in the construction of human simulacra as early as 1949, when "Sierra Sam" was created by Samuel W. Alderson at his Alderson Research Labs (ARL) and Sierra Engineering Co. to test aircraft ejection seats and pilot restraint harnesses. This testing involved the use of high acceleration to 1000 km/h (600 mph) rocket sleds, beyond the capability of human volunteers to tolerate. In the early 1950s, Alderson and Grumman produced a dummy which was used to conduct crash tests in both motor vehicles and aircraft.

The mass production of dummies afforded their use in many more applications.

Alderson went on to produce what it called the VIP-50 series, built specifically for General Motors and Ford, but which was also adopted by the National Bureau of Standards. Sierra followed up with a competitor dummy, a model it called "Sierra Stan," but GM, who had taken over the impetus in developing a reliable and durable dummy, found neither model satisfied its needs. GM engineers decided to combine the best features of the VIP series and Sierra Stan, and so in 1971 Hybrid I was born. Hybrid I was what is known as a "50th percentile male" dummy. That is to say, it modeled an average male in height, mass, and proportion. The original "Sierra Sam" was a 95th percentile male dummy (heavier and taller than 95% of human males). In cooperation with the Society of Automotive Engineers (SAE), GM shared this design, and a subsequent 5th percentile female dummy, with its competitors.

Since then, considerable work has gone into creating more and more sophisticated dummies. Hybrid II was introduced in 1972, with improved shoulder, spine, and knee responses, and more rigorous documentation. Hybrid II became the first dummy to comply with the American Federal Motor Vehicle Safety Standard (FMVSS) for testing of automotive lap and shoulder belts. In 1973, a 50th percentile male dummy was released, and the National Highway Transportation Safety Administration (NHTSA) NHTSA undertook an agreement with General Motors to produce a model exceeding Hybrid II's performance in a number of specific areas.

Though a great improvement over cadavers for standardized testing purposes, Hybrid I and Hybrid II were still very crude, and their use was limited to developing and testing seat belt designs. A dummy was needed which would allow researchers to explore injury-reduction strategies. It was this need that pushed GM researchers to develop the current Hybrid line, the Hybrid III family of crash test dummies.

[modifica] Hybrid III family

The original 50th percentile male Hybrid III's family expanded to include a 95th percentile male, 5th percentile female, and three-year-old and six-year-old child dummies.

Hybrid III, the 50th percentile male dummy which made its first appearance in 1976, is the familiar crash test dummy, and he is now a family man. If he could stand upright, he would be 168 cm (5'6") tall and would have a mass of 77 kg (170 lb). He occupies the driver's seat in all the Insurance Institute for Highway Safety (IIHS) [1] 65 km/h (40 mph) offset frontal crash tests. He is joined by a "big brother", the 95th percentile Hybrid III, at 188 cm (6 ft 2 in) and 100 kg (223 lb). Ms. Hybrid III is a 5th percentile female dummy, at a diminutive 152 cm (5 ft) tall and 50 kg (110 lb).^[6] The two Hybrid III child dummies represent a 21 kg (47 lb) six year old and a 15 kg (33 lb) three year old. The child models are very recent additions to the crash test dummy family; because so little hard data are available on the effects of accidents on children, and such data are very difficult to obtain, these models are based in large part on estimates and approximations.

[modifica] Test process

Every Hybrid III undergoes calibration prior to a crash test. Its head is removed and is dropped from 40 centimetres to test calibrate the head instrumentation. Then the head and neck are reattached, set in motion, and stopped abruptly to check for proper neck flexure. Hybrids wear chamois leather skin; the knees are struck with a metal probe to check for proper puncture. Finally, the head and neck are attached to the body, which is attached to a test platform and struck violently in the chest by a heavy pendulum to ensure that the ribs bend and flex as they should.

When the dummy has been determined to be ready for testing, it is dressed entirely in yellow, marking paint is applied to the head and knees, and calibration marks are fastened to the side of the head to aid researchers when slow-motion films are reviewed later. The dummy is then placed inside the test vehicle. Forty-four data channels located in all parts of the Hybrid III, from the head to the ankle, record between 30 000 and 35 000 data items in a typical 100 - 150 millisecond crash. Recorded in a temporary data repository in the dummy's chest, these data are downloaded to computer once the test is complete.

Because the Hybrid is a standardized data collection device, any part of a particular Hybrid type is interchangeable with any other. Not only can one dummy be tested several times, but if a part should fail, it can be replaced with a new part. A fully-instrumented dummy is worth about €150 000.^[7]

[modifica] Hybrid's successors

Hybrid IIIs are designed to research the effects of frontal impacts, and are less valuable in assessing the effects of other sorts of impacts, such as side impacts, rear impacts, or rollovers. After head-on collisions, the most common severe injury accident is the side impact.

The SID (Side Impact Dummy) family of test dummies has been designed to measure rib, spine, and internal organ effects in side collisions. It also assesses spine and rib deceleration and compression of the chest cavity. SID is the US government testing standard, EuroSID is used in Europe to ensure compliance with safety standards, and SID II(s) represents a 5th percentile female. BioSID is a more sophisticated version of SID and EuroSID, but is not used in a regulatory capacity.

BioRID is a dummy designed to assess the effects of a rear impact. Its primary purpose is to research Whiplash, and to aid designers in developing effective head and neck restraints. BioRID is more sophisticated in its spinal construction than Hybrid; 24 vertebra simulators allow BioRID to assume a much more natural seating posture, and to demonstrate the neck movement and configuration seen in rear-end collisions.

THOR offers sophisticated instrumentation for assessing frontal-impacts.

CRABI is a child dummy used to evaluate the effectiveness of child restraint devices including seat belts and air bags. There are three models of the CRABI, representing 18-month, 12-month, and 6-month old children.

THOR is an advanced 50th percentile male dummy. The successor of Hybrid III, THOR has a more humanlike spine and pelvis, and its face contains a number of sensors which allow analysis of facial impacts to an accuracy currently unobtainable with other dummies. THOR's range of sensors is also greater in quantity and sensitivity than those of Hybrid III.

Further development is needed on dummies which can address the concern that, even though fewer lives are lost, there are still a hundred seriously injured passengers for every death, and crippling injuries to the legs and feet represent a great percentage of resultant physical impairments.

[modifica] Future of the dummy

Crash test dummies have provided invaluable data on how human bodies react in crashes and have contributed greatly to improved vehicle design. While they have saved millions of lives, like cadavers and animals, they have reached a point of reduced data return.

The largest problem with acquiring data from cadavers, other than their availability, was that an essential element of standardized testing, repeatability, was impossible. No matter how many elements from a previous test could be reused, the cadaver had to be different each time. While modern test dummies have overcome this problem, testers still face essentially the same problem when it comes to testing the vehicle. A vehicle can be crashed only once; no matter how carefully the test is done, it cannot be repeated exactly.

A second problem with dummies is that they are only approximately human. Forty-four data channels on a Hybrid III is not even a remote representation of the number of data channels in a living person. The mimicking of internal organs is crude at best, a fact that means that even though cadavers and animals are no longer the primary sources of accident data, they must still be employed in the study of soft tissue injury.

The future of crash testing has begun at the same place it all started: Wayne State University. King H. Yang is one of Wayne State's researchers involved in creating detailed computer models of human systems. Currently, computers are neither fast enough nor programmers skilled enough to create full-body simulations, but injury analysis of individual body systems is producing reliable and encouraging results.

The advantage of the computer is that it is unbound by physical law. A virtual vehicle crashed once can be uncrashed and then crashed again in a slightly different manner. A virtual back broken can be unbroken, the seatbelt configuration changed, and the back re-broken. When every variable is controllable and every event is repeatable, the need for physical experimentation is greatly reduced.

At the beginning of the 21st century, legal certification of new car models is still required to be done using physical dummies in physical vehicles. However, the future is almost certainly one where neither skin and bone, or plastic and steel will determine the shape of vehicles to come. The next generation of crash test dummies will perform their tasks entirely on a computer screen.

[modifica] See also

• Car accident
• Car safety
• Crash test
• Safety car
• Seat belt legislation
• Samuel W. Alderson
• Harold Mertz
• Crash test dummies in popular culture

[modifica] Footnotes

[modifica] References

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