Laceration and Ejection Dangers of Automotive Glass, and the Weak Standards Involved. The Strain Fracture Test.

Abstract

Glazing types are historically described, with the laceration injuries and ejection deaths associated with present glazing. Sixty tempered glass windows manufactured at nominally four temper levels were tested for uncracked fracture fragment size and weight and length by the American and European standards, which fracture the glass without strain, and our preliminary strain fracture test, which produces longer uncracked fragments and heavier clusters of fragments. Our study relates the results by the three methods to the temper measurements using birefringence, with a discussion of alternate safer glazing and the inadequacy of present standards for reducing laceration and ejection dangers.

Automobile glazing in the United States is primarily the three ply (annealed glass/polyvinyl butyral or PVB plastic interlayer/annealed glass) laminated windshield, and tempered glass side, rear, and roof windows. The first windshields, about 1903 in the United States, and soon after the first glass windows, were of plate glass, which breaks into long, sharp, dangerous shards. Henry Ford introduced the laminated windshield, first developed in Europe, for the Model T in 1927, and soon after the windows were also with laminated glazing. The plastic interlayer holds together the pieces of glass when broken, greatly reducing the danger.

Tempered glass for automobiles was developed in Europe, and soon was considerably less expensive than laminated glazing. It was first introduced in the United States in a Chrysler model in 1936. Tempered glass side and rear windows were gradually introduced in other models and by other manufacturers, essentially replacing laminated side and rear windows by 1961, with contested arguments that tempered glass was better for side windows than laminated glazing [for example, Severy and Snowden, 1962].. In the United States, the windshield remained of laminated glass, with its ability to prevent the penetration into the occupant compartment of a heavy object that would shatter tempered glass. In today’s manufacture, molten glass floating on a hot bath of liquid tin, “float glass,” is drawn off on rollers then cooled slowly to become annealed glass. The glass is cut to the window size and any necessary holes are cut. The glass is reheated, given the needed curvature in a mold, then blasted on both sides by cool air, causing a shrinkage or compression of the surfaces. This makes tempered glass have a harder surface, resisting fracture when struck by a blunt object under loads that crack the annealed glass of windshield type laminated glazing. But when the tempered glass is fractured, it shatters, scattering the glass fragments and opening out the window. The laminated glazing may be cracked but the plastic interlayer holds the glass pieces together and keeps the window closed. It takes more than three times the kinetic energy of a blunt object to penetrate through a typical laminated glazing than to shatter and penetrate through tempered glass. Note also that a blow with a sharp object, such as an awl or prick punch, can shatter tempered glass with very little energy input.

Injuries involving glazing include primarily lacerations from broken glass and ejections through the glazing areas. It is this occupant ejection component of the glazing failure modes that is the most dangerous aspect of tempered glass. For averaged values in the period of 1988–1993 [Harper et al., 1995], about 30,000 people were killed each year in crashes of light vehicles (passenger cars, and light trucks and vans and sport utility vehicles). Of these, 10,900 were killed with whole body or partial ejection, 36% of those killed. Sixty one percent of those killed with ejection were killed in rollover crashes. Of those ejected, about 7500 were killed with ejection through glazing areas, with 5400 of these ejected through the front side windows. Passenger cars roll over in crashes less often than light trucks and vans and sport utility vehicles, with about 20 to 25% of occupants killed in all crashes in passenger cars killed with ejection, and about 40% of occupants killed in crashes in light trucks and vans and sport utility vehicles killed with ejection.

The earlier work of one of us [Clark and Sursi. 1984, 1985, 1989] indicated this need to reduce ejection by returning to laminated glazing, with experiments utilizing the two ply or glass-plastic laminated glazing, with its greater laceration reduction as well as ejection reduction qualities. Also, this and our earlier unpublished work included the development of the “T-edge” encapsulation of the front and rear edges of movable (side window) glazing in order to transfer window loads to the window frame. The T-edge is trapped in the front and rear channels of the window, allowing the glazing to go up and down but preventing the cracked glazing from pulling out of the channels, thus maintaining the ejection reduction quality through the strength of the stretching plastic layer or layers. Clark (1989) also suggested the use of an 18 kg (40 pound) spherical test object moving at 33 km/h (20 mph) perpendicular to the glazing planes to test the adequacy of the laminate strength, after finding that the maximum “effective mass” of a dummy collapsing against a window glazing approximates that of the 40 pound test weight, and that the preliminary commercial laminated glazing adequately framed could resist ejection at this test speed

In the recent twenty years, the percentages of occupant deaths that involve ejection have not changed very much although seat belt use has increased from 10% to 66% [Harper, 1995]. Although death with ejection is rare for those wearing belts, enough people - and most of us occasionally - don’t wear their belts, and some never do - and these drivers tend to be younger and drive faster and drive late at night with other young people and do not restrain their children. Until that high risk population also has reliable restraints, the percent of occupant deaths that involve ejection remains essentially independent of the percent of the population using their seat belts.

In Europe, three ply laminated side and rear window glazing is beginning to be used again, by some models of Audi, BMW, and Volvo cars, with benefits claimed for sound reduction and particularly theft reduction due to the difficulty of breaking through the plastic layer of the laminated glazing, but also ejection reduction. It is noted also that the growing use of side airbags can reduce side window ejection.

The experimental work of this paper deals with means to reduce the laceration potential of tempered glass, and particularly the significance of strain of the glass when broken in affecting the potential of the fragments for producing lacerations.

The motor vehicle industrial glazing standards, in the United States ANSI/SAE Z-26.1-1996 [American Standards Institute, 1996] and in the European Community 92/22/EEC [European Economic Community, 1992], in their fracture tests of tempered glass both fracture the glass with an abrupt impact of a sharp pointed prick punch or hammer while the glass is supported without strain. The American test requires that any fragment free of cracks shall weigh less than 4.25 grams. The European standard requires that a five centimeter square area of the contact blueprint of the fragments shall include at least 40 fragments, but less than 400. The industry view was that these tiny fragments, “dice like” with 90 degree not very sharp edges, would bounce off the skin without causing lacerations. Both standards exempt fragments near the impact points or near the edges of the glass.

When tempered glass is broken in a crash, most of the pieces have internal cracks, and these “clusters” of fragments [Severy, 1962] can lacerate, weighing much more than 4.25 grams, and with edge angles less than 90 degrees, and some with sharp points. Our work [Yudenfriend, 1996; Yudenfriend and Clark, 1997] has shown that when tempered glass is strained before it fractures, the fracture planes are less rectilinear. Clusters weighing 62 grams, some with fracture planes within the thickness but not penetrating to the surface, and flat spike-like pieces called splines over 150 mm long, can be produced. Green (1999), and Gulati (1997) report similar characteristics of fracture with strain. Since glazing is broken in vehicle crashes typically with some strain by frame deformation or body or object contact, not by a prick punch, our interest is to modify the fracture tests to better represent the fracture dynamics of road crashes. Road crashes do produce lacerations from glazing, with NHTSA reporting for 1996, in response to a letter request, that there were a (rounded off) estimated 215,000 lacerations from windshield contact, 18,700 lacerations from side and rear window contact, and 250,000 lacerations from flying glass.

When tempered glass is manufactured, the hot glass is abruptly cooled by blasts of air on both sides, causing a compression or increased density of the surface, further increased as the core cools. With this density gradient, tempered glass viewed on edge is birefringent, that is, the light electric vector oscillation parallel to the surface has a greater refractive index than the electric vector perpendicular to the surface. The greater the temper of the glass, or its abruptness of surface cooling in manufacture, the greater the birefringence. Hence the magnitude of temper can be measured by the magnitude of the birefringence.

When tempered glass is strained by increasing bending, the surface made more concave is put into greater compression and the surface made more convex has the compression reduced, until finally the glass fractures, initially on the side made more convex, with some flying glass fragments thrown from the strained glass at at least 60 km/h [Yudenfriend, 1997].

MATERIALS AND METHODS

Special arrangements were made with Glasstech, Perrysburg, Ohio, an automotive glass manufacturer, to obtain 60 3.5 mm thick clear automobile rear windows prior to tempering, and to control the subsequent heating, and the quenching air jets, so that four groups of windows with differing temper were produced. These 60 windows were then measured for surface compression on the inboard or concave surface by staff of Strainoptic Technologies, using the American Society for Standards and Materials (1994) ASTM Standard C-1279 method with the laser beam Grazing Angle Surface Polarimeter (GASP) [Redner, 1990, 1991]. Measurements were taken at the center of the glazing, at left and right points 19 cm from the corresponding edge, and on the vertical midline 10.5 cm from the bottom and 16.5 cm from the top edge. Surface compression for the five measurement points for each glass window were recorded, and averaged for the fifteen windows of each group..

The windows were then shipped to Automotive Glass Engineering, Kansas City, where transmission birefringence photographs of the windows between crossed polarizers were taken. The window for testing was mounted in front of a sheet polarizer in front of a light box. The window was photographed with an analyzer in the crossed position. These transmission birefringence photographs provide only a qualitative indication of the nonuniformities of glass density for a light beam traveling perpendicular to the glass surface. However, changes in appearance of the photographs provide an indication of changed conditions of the glass, and so can alert production staff to checking the tempering air jets and measuring the temper.

The window glass was nested in a second window glass, with a piece of high sensitivity blueprint paper between the two windows. The windows were then broken using a prick punch at the position specified in the standard. The largest piece without cracks was weighed, for pieces outside of the excluded areas. Likewise for the 92/22/EEC Directive Fragmentation Test, the prick punch was applied successively at one of each of the four points specified by the 92/22/EEC Directive, page 65, and contact blueprints were made within the specified times after impact.

Contact blueprints of the shattered windows are required by the European Community regulation. The blueprint paper was exposed after glass fracture to the light from 12 quartz halogen lamps. The number of fragments (pieces delineated with dark fracture lines) in any square area 5 centimeters on a side, outside of the excluded areas, was estimated, to see if any square had less than 40 fragments. Also, for the Z26.1-1996 test, for each window, the largest piece with no cracks after the window was shattered by the prick punch was weighed.

To develop a fracture test with additional strain of the glazing, a method similar to that of our earlier study [Yudenfriend, 1997] was utilized, but with the center contact being a prick punch point rather than a roller. The point was pressed hydraulically vertically down into the window on its concave side, moving at about 25 mm per second, until the window shattered. The window was mounted over blueprint paper on 76 mm thick foam rubber on a flat rigid surface. The point was hemispherical with a diameter of 0.2 +/− 0.05 mm, as in the other standards. The shattered pieces were caught on the blueprint paper surface. The longest and heaviest pieces free of cracks was measured or weighed. The number of fragments in a 5 cm square estimated to have the fewest fragments was noted as more or less than forty.

Note that each of the window samples was fractured by one of the three methods and evaluated by all three methods, although the EEC test was evaluated in most cases only at the pass/fail level..

RESULTS

The transmission birefringence photographs, of the windows viewed between crossed polarizers, showed light spots, marking the higher birefringence or temper where the air jets hit the glass. In this glazing production, the jets were not oscillated. These temper “peaks” were about 14 to 21 MPa above the temper of the areas not directly hit by the cooling air jets. This temper variation can lead to less uniform fracturing. Continuous production line monitoring of the tempered glazing birefringence could provide an early warning of developing tempering inadequacies.

Table 1 (NOTE: Tables 1 and 2 of this paper are in an addendum which will be provided electronically by contacting the first author at ccyclark@aol.com.) gives the GASP readings for these windows, after translation to megapascals of compression, in accordance with ASTM Test Method C1279 [ASTM, 1994]. The attained levels of temper for the different groups were not as distinctive as we had hoped, and the variation of temper at the different points of one window was greater than we had hoped. The Group #1 windows had a surface compression level that was substantially higher than the other groups. Groups #2, #3, and #4 surface compression levels are more nearly alike, although a trend was suggested, with #2 the lowest temper, and #3 expectedly borderline as to passing the Z-26 standard, and #4 samples possibly able to pass Z-26.

Table 2 (See Table 1 NOTE) shows the results of the fracture testing of the 60 windows, as evaluated by the three methods. The test columns are marked SAE for the Z-26 Fracture Test, EEC (with the number representing the point of fracture contact) for the EEC Fragmentation Test, and SFT for the strain fracture test. Window 1–14 and window 4-1 were broken before testing was completed. SC MIN is the minimum surface compression in megapascals measured at any of the five designated measurement points. Weight is in grams and length in millimeters, for the heaviest and longest fragments without internal cracks. F = failed; P = passed the test conditions of the three different standards.

With 60 windows there were nominally five windows at each of four temper levels and broken by the three fracture test methods, with slight differences. In Table 3, the measurements are combined for all four groups. The lengths and weights of the longest and heaviest uncracked fragment were analyzed, and the means and standard deviations presented for the three different test methods. The standard deviations are large, but the lengths of the largest strain fracture test fragments (“SFT”) are notably greater than the lengths of the fragments of the two unstrained fracture tests for these combined samples predominantly tempered below the usual production level.

Table 3.

presents the Basic Statistics of the Heaviest and Longest Uncracked Window Fragments by Test Method, with the Group Values Combined

	Mean	Standard	Number
Weightgrams		deviation	measured
SFT	12.539	12.707	18
EEC	11.476	10.807	17
SAE	10.807	10.319	23
Length millimeters
SFT	138.944	74.517	18
EEG	85.412	58.114	17
SAE	75.435	50.307	23

The level of temper of the windows is also important as to the length and weight of the fragments. Table 4 presents these data.

Table 4.

Basic Statistics (mean/standard deviation) of the Heaviest and Longest Uncracked Fragments, by Temper Group and Test Method

Temper:	Highest	Lowest	Moderate	Higher
	Group 1	Group 2	Group 3	Group 4
	Weight, grams
SFT	0.413/0.140	30.488/8.951	11.384/2.757	3.675/0.689
EEC	0.685/0.422	26.402/3.985	10.438/2.519	4.650/2.261
SAE	0.345/0.097	27.500/5.777	11.917/1.021	6.250/2.092
	Length, millimeters
SFT	41.500/17.540	222.0/12.962	172.800/33.937	90.250/12.997
EEC	19.250/12.285	153.4/34.638	91.250/33.009	60.750/27.837
SAE	16.000/2.608	147.0/31.686	85.500/24.793	65.167/10.108

Note that these tables are for fragments without cracks. The cluster fragments of tempered glass windows shattered in the vertical position, with many cracks but not all aligned or of full thickness, and so holding together after striking the collecting towels, are far heavier, or longer, or pointed with some fragments with edges of less than full thickness, and so quite sharp We believe a better measure of the strain effect would be provided by counts and measurements of these cluster fragments with cracks.

It can be observed from Table 4 that both the weights and lengths of the heaviest and longest uncracked fragments are in a qualitatively inverse relation to the level of temper, and that the lengths of the fragments (SFT) broken with slowly applied external strain stand out as notably greater than the lengths of fragments broken with the abruptly applied (prick punch) fractures.

All windows with minimum measured surface compression above 103 MPa (15,000 psi) which were broken according to the SAE protocol met the Z26.1 1996 standard criterion. Two windows with minimum surface compressions above 103 MPa, one broken with the SFT protocol with 109 MPa and one broken with the EEC protocol with 115 MPa, failed to meet the Z26.1 weight criterion.

Every window with a minimum surface compression above 117 MPa (17,000 psi) met the EEC criterion of more than 40 fragments in the least populated square of 5 cm on a side, observed on the contact blueprint, independent of the protocol used to break the windows. Only four windows with minimum surface compression values below 117 MPa met the criterion. None of the four was below 93 MPa (13,500 psi) at any measured point.

If 38 mm is taken as the maximum accepted uncracked fragment length for the initial strain fracture test criterion, all but one window in Group 1 (highest temper) would have passed. If the criterion were set at 50 mm, only three beyond those in Group 1, with these three all in Group 4 (next to the highest temper), would pass.

DISCUSSION

We have worked to develop a Strain Fracture Test that strains tempered glass to failure, and have observed that glass with a minimum surface compression at any of the five designated points of measurement of less than 103 MPa (about 15,000 psi) when strained to fracture produces significant numbers of sharp fragments, heavy sharp clusters, and long splines, with lesser effects of strain at higher temper. Further study is needed (1) to establish this dangerous level more precisely, (2) to quantify the sharpness and clustering effects, and (3) to establish the minimum temper anywhere on a glazing to provide a reasonable and practicable level of expected laceration injuries due to tempered glass shattered, generally under strained conditions, in road crashes. A reproducible way is needed to separate the clusters and fragments, and measure their sharpness and the forces holding the clusters of fragments together. We suggest the minimum temper should be at about 138 MPa (about 20,000 psi). Our measurements of road car windows suggest that many are below this level.

Further study is also needed of the means to strain the glazing before fracture. The strain level at fracture for the sharp point used in this work, even when slowly advanced, may be too dependent on local conditions commensurate with the dimensions of the point. Straining the full sized glazing mounted on a rigid frame with a more blunt object, possibly even a dummy headform slowly advanced, may give more consistent results.

Indications from our previous work are that some production motor vehicle tempered glass windows which pass Z-26.1-1996 have a low enough temper to produce dangerous fragments when strained in a road crash. We suggest consideration of replacement of the American and European automotive industrial fracture test by a strain fracture test after further development, carried out on full size windows. We suggest the use of continuous birefringence monitoring on tempered glass production lines, to insure the maintenance of sufficient and uniform tempering.

Looking beyond the affect of strain on the laceration potential of tempered glass, we note many studies of the measurement and consequences of laceration and ejection injuries, and the means to reduce these injuries. With regard to laceration, the major advance was the doubling of thickness of the PVB interlayer of laminated glazing in 1965 – 66, to 0.76 mm. This change to “High Penetration Resistant” (HPR) laminated glazing for the windshield was made by the automobile industry without regulation and just before the establishment of the National Highway Safety Bureau - now the National Highway Traffic Safety Administration (NHTSA). This has greatly reduced head penetration through the windshield with the consequent severe neck lacerations and fatalities. Patrick and Daniel (1964) review the developmental work. Making a thinner but tempered inner sheet of the laminated glazing was found to reduce lacerations in laboratory tests in the United States [Blizard and Howitt, 1970] and in Europe [Plumat, Van Laethem, and Baudin, 1971], but this approach was not used in United States windshield production. The method of partially tempering the glass sheets in laminated glazing was further developed by the Triplex Safety Glass Company, with reduced laceration demonstrated by the Triplex Laceration Index [Pickard, Brereton, and Hewson, 1973; Kay, Pickard, and Patrick, 1973]. Careless and Mackay (1983) discuss the relation of the skin simulants used in laceration testing to skin of cadavers of various ages and from different body parts. Jettner and Hiltner (1986) review laceration measurements and select a pass/fail criterion for these largely minor injuries. Partial tempering of the glass sheets of side window laminated glazing is now going into prototype production [Solutia, Inc., 2000].

Following the HPR advance, the next major significant advance for reducing lacerations has been the addition of a plastic layer or layers as the inboard layer of the windshield laminated glazing. This went into production, as the “Securiflex” windshield by Saint Gobain Vitrage in Europe, eliminating lacerations due to windshield cracking or head contact in simulated barrier crashes up to 65 km/h [Patrick and Chou, 1976], with further studies including road use [Jandeleit and Orain, 1977]. Saint Gobain Vitrage petitioned NHTSA to allow the use of Securiflex in the United States, and after study [Wakeley, 1983], Federal Motor Vehicle Safety Standard 205, Glazing Materials, was modified in 1986 to allow the use of “glass- plastic glazing” as any laminated glazing with a plastic layer on the inboard surface, and meeting specified tests, including allowing more haze development with abrasion than is allowed for a glass inboard surface. In this period also, General Motors, working with DuPont and LOF,. produced and marketed an “Anti-Lacerative Windshield” with a different plastic formulation. After three years of production, in a cost-cutting period, General Motors ceased production of this safety advance, reporting public concern for the greater ease of scratching this inboard plastic layer than for glass. Meanwhile, “two ply” glass plastic glazing, with one layer of glass and the plastic inboard layer, was developed by DuPont and LOF [Johnston, Herliczek, and Ash, 1974] and others, and tested for side window [see for example Clark, 1984, 1985, 1989] and windshield use.[Browne, 1993], but these have not been put into production. Miller and Sykes (1998) report on the progress to make a solid plastic (polycarbonate) side window able to meet suggested laceration and head impact and ejection performance criteria. It is expected that less easily scratched plastic surfaces will be developed, so that more complete laceration protection, as well as ejection protection, can be provided.

Ejection reduction is the far more serious problem for glazing than laceration reduction. Early studies [Huelke and Gukas, 1966] noted ejection as a major cause of road deaths, but this was attributed more to door opening than window ejection until improved door locks were developed. The Europeans tested glass impacts with a 10 kg “headform,” representing the weight of the head and partial weight of the upper body of a person leaning into a glazing impact. This headform gave some semblance of ejection testing. Unfortunately, the FMVSS 205 fracture tests, with a one foot square glazing sample, emphasized only the initial fracturing of the glazing sample. Widman (1965) noted the correlation of the penetration level of the European 10 kg headform falling on the 2 × 3 foot glazing to the penetration level of a five pound ball falling on a 1 × 1 foot glazing sample, and the Federal standard has still not been modified to test the possibility for ejection of body weight objects through tempered glass.

It is the plastic layer that provides the possibility for ejection reduction, of the interlayer of a three ply laminated glazing of the HPR windshield type or of the recent three ply laminated side windows, or of the inboard plastic layer of two ply glass-plastic glazing. Tempered glass alone when cracked shatters, and provides no further ejection protection. With the appropriate inboard plastic layer added to the tempered glass, Clark (1989) has demonstrated ejection prevention of a 40 pound (18 kg) headform moving at 20 mph (33 km/h) with one prototype glass-plastic side window formulation, using either a bonded in place window or a movable (up and down) side window using the suggested “T-edge” design. Clark estimates that T-edge two ply glass-plastic glazing would prevent the ejection through windows of essentially all pre-teen children and almost half of the adults currently ejecting. NHTSA staff more conservatively estimate that 500 to 1300 people would be saved each year if “advanced glazing,” with a plastic layer and side channel retention, were used in just the front side windows [Wilke et al., 1999].

Unfortunately, the weak Federal glazing standard has still not been modified to directly measure laceration or ejection capability, with required performance levels. Window ejection is affected by the mounting of the glazing in the channels (of a movable window}and in the frame, yet the Federal standard tests only a one foot square sample of the glazing alone. One concession was made in 1991: the two ply glass-plastic glazing may be clamped in the test frame before testing if the five pound ball will pass through the test frame. This glazing when cracked may collapse through the frame with the ball, clearly not a test of the penetration of the ball through the glazing itself. With the HPR laminated glazing, the cracks in the glass panes on the two sides of the glazing do not line up, so that the sample stops the ball and does not fall through the frame at the required performance level.

The tempering process with air jets for making tempered glass does not produce a uniform temper over the entire glazing surface. The one foot square glass sample for testing should have the same temper as the full glazing manufactured, yet there is no requirement for testing the temper levels. Hence any government test of a small sample provides no adequate indication of the full glazing performance. The European glazing standard requires testing of the full size glazing. Finally, our work indicates that strain of the glazing before fracture does change the fracture characteristics and hence the laceration potential of the glazing. We recommend the addition of a strain fracture test to the standards.

SUMMARY AND CONCLUSIONS

We have tested 58 automobile windows of four nominal levels of temper by the Fracture Tests of Z36.1-1996 and 92/22/EEC, and the proposed new strain fracture test. We suggest that the new test with strain provides glass fracture conditions closer to those of road crashes, and so if introduced, after further refinements, into the standards and regulations could lead to lower levels of laceration and other glass injuries in road crashes. For a 3.5 mm thick automobile rear window, preliminary indications are that a minimum surface compression or temper of about 138 MPa (20,000 psi) of a glazing (anywhere on the surface) when given the strain fracture test will provide a glazing that will meet the suggested criterion. Glass with a lower temper may fail this criterion, with longer and more dangerous splines and fragments.

Further study is needed for the distribution of the minimum surface compression of automotive tempered glass presently on the road. How much of the problem of flying glass injuries is due to motor vehicles having glazing with a minimum temper below 138 MPa? What percent of automotive tempered glass windows now on the road would not comply with FMVSS 205 Test 7 - if applied to the full glazing?

It is clear, however, that external strain of automobile tempered glass windows, as by frame deformation in a crash or by the strain fracture test, increases the length and hence the laceration and skin penetration danger of tempered glass fragments when the glass shatters, over the length of fragments without external strain. Hence the safety of such glass should be evaluated using a test involving external strain of the glass before fracture.

We have briefly noted some of the studies of the broader context of glazing safety work, including means to measure laceration and designs of glazing to reduce lacerations and ejection.

We acknowledge with thanks the work of the staffs of Glasstech and Strainoptic Technologies, and particularly of Henry Chamberlain and Michael Shields, of Automotive Glass Engineering, for the glazing production and the measurements of this study.

(Presenter: Carl Clark)

Ed Moffatt: Just a comment on the rollover that you showed. That was one of the Malibu rollover tests. It was not a gasket mounted windshield. Rather, it was a bonded windshield on that vehicle and the ejection of the dummy was through a tear in the laminate in the bonded windshield. The window remained attached through its periphery. So although I share with you the idea that laminated glass offers a lot of containment, that is in fact an example of a laminated glass windshield which tore through the laminate and allowed the dummy to be ejected.

C. Clark: You see at the end of that video the whole windshield coming out. There may have been some pieces around the edges, but I think if it was an attached bonded windshield that was bonded with butyl rubber and not polyurethane … you did those tests, did you, Ed?

E. Moffatt: You are wrong.

C. Clark: I’m wrong. Okay. You can get through windshields. That’s still true. That was a high speed crash.

M. Mackay: One point of historical correction in terms of the St. Gobain Securiflex. It was, in fact, shown not to be satisfactory in terms of everyday performance. The problems of scraping the inside polyurethane layer were substantial. There were lots of complaints, and I think it is a distortion to suggest that it was a satisfactory product in Europe.

Secondly, the issue of severity of soft tissue injuries – lacerations – from tempered glass. In our experience in the studies we’ve done over the years, although you may look at some of these clusters of glass, the actual accident data suggest that the lacerations that come from tempered glass are in the great majority of cases trivial. They may be in the short term somewhat unsightly, but it isn’t a major issue in terms of side window glazing. It used to be, of course, in the bad old days when we had tempered windshields, but the kinematics are quite different.

One final word of caution in that once you start putting in a structure that is going to contain an occupant, the issue of the actual loads on the head, particularly when you’re loading the brain in the coronal plane and generating angular accelerations, suggests that, firstly, the HIC in that context is not the best parameter, and that, secondly, one of the things you haven’t discussed, Carl, is in fact the specific brain injury risk from hitting a structure of whatever kind in the side impact condition.

C. Clark: I certainly accept that laceration is the minor part of the problem. It is ejection we need to reduce. I do feel we can go a long way to soften the interior of cars. Way back, I suggested what I called the airpads over every hard structure so that when you inflated the major airbag, you inflated everything up from the soft structures. But this is in the future and I certainly accept that you can get hurt on the inside. We need to do more about that.

Alan German: I believe the effectiveness of laminated glass in those NHTSA studies is very strongly dependent upon restraint usage. I wonder if society isn’t better off putting its money into seat belt promotion and enforcement campaigns rather than laminated glazing.

C. Clark: Were you aware of the point I made that the percent of people in the United States killed by ejection has not gone down as seat belt use has gone from a few percent to 70%. That is a very impressive point to think about, and indeed in other studies, the number of children that are unrestrained is a high percentage — about 25% of children are unrestrained — and I think there is a subpopulation — all of us who don’t use their belts all of the time — but are we just going to let these people die or can we do something about them as well.

Bob Sproat: I am interested to know whether you perceived an increased risk of entrapment in vehicles using laminated glass. I’m thinking in terms of the emergency services’ point of view, but also if all four doors of the car are jammed, whether the car be lying on its side or the car doors are jammed by collision, how easy it would be to get to the casualties inside, particularly if it was necessary to render immediate first aid such as clearing or maintaining an airway. It seems to me that if you have a situation where it’s very difficult to break windows to get inside to release an occupant or to render first aid, you’re putting lives at risk in this way.

C. Clark: There would be a problem. The EMS people can go through these kinds of laminated glass with a sharp knife, but indeed the people on the inside should have a way to get out and perhaps we should think about that. Buses have a way to open the plastic windows by pulling at a certain point and the windows pop out. Maybe we need to think of that.

Don Reinfurt: Just to end on a bit of levity. Alfred Hitchcock was known for appearing in his films. Were you the thief trying to break into the side of the car?

C. Clark: No. (audience laughter)

Figure 1.

shows a contact print of the fracture fragments of a high temper window - window 1–12, broken by the EEC method using EEC impact point 4. The center of the area shown is 76 cm from this impact point.

Figure 2.

shows a part of the contact photograph of the fragments of a window with low temper when fractured by a prick punch applied at the center. A 5 × 5 cm square is marked on the photograph. Any fragment which extends outside of the 5 cm square area is counted as only half a fragment. The count within this square is less than 40, indicating that this window would not pass 92/22/EEC.