Interpretation ID: 77-1.32
TYPE: INTERPRETATION-NHTSA
DATE: 02/25/77
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: Ward School Bus Mfg., Inc.
TITLE: FMVSS INTERPRETATION
TEXT: This responds to your December 7, 1976 and January 8, 1977, questions whether 53 described intersections of bus body components qualify as "body panel joints" subject to the requirements of Standard No. 221, School Bus Body Joint Strength. This also responds to your question whether the seating reference point in Standard No. 222, School Bus Passenger Seating and Crash Protection, can be located using nominal seat cushion deflection.
The terms which establish the applicability of the requirements of the standard to a particular section of a school bus body are defined in S4 of the standard. Read together, they establish the following test. If the edge of a surface component (made of homogeneous material) in a bus that encloses the bus' occupant space comes into contact or close proximity with any other body component, the requirements of S5 apply, unless the area in question is designed for ventilation or another functional purpose or is a door, window, or maintenance access panel. Applying this test to the 53 intersections of bus body components you describe, it appears that the areas corresponding to the following numbered paragraphs of your letter are bus body joints and therefore must meet the 60-percent joint strength requirements: 1 through 34, 36, 37, 39, 42, 44, 45, 46, 51. Additionally the joint described in your January 8, 1977, submission must comply with the standard.
The illustration accompanying paragraph 16 shows a second joint between a door post and exterior trim panel with the notation that this joint is "Not Required To Meet Std." The agency concludes that this joint also must meet the requirements of the standard, because it is a connection of a body component with a body panel that encloses occupant space.
The lower skirt section described in paragraph 35 is not a body panel that encloses occupant space, because it is located entirely below the level of the floor line and, therefore, is excluded from the standard's requirements.
In the control console area, the interior side panel described in paragraph 38 and the shoulder cap (wire cover) described in paragraph 43 are considered maintenance access panels, whose joining with the bus body is excluded from the requirements only if a wire is installed behind them.
The turn signal housings described in paragraph 40 and 41 are not considered to have a function in enclosing the occupant space and are therefore not considered body components for purposes of the requirements.
The front and rear headers described in paragraphs 47 and 48 are considered primarily structural and have only an incidental role in enclosing the occupant space and, therefore, are not considered "body panels" for purposes of the requirements.
The rubrail described in paragraph 49 is not considered to have a function in enclosing the occupant space and, therefore, is not considered a body component for purposes of the requirements. For purposes of testing the complex joints to which it is fastened, it should be modified as necessary to prevent it from affecting testing of the underlying joint.
Because the plywood described in paragraph 50 is attached to a floor panel and is only added to some buses for insulation purposes, it is not considered to have a function in enclosing the occupant space and is therefore not considered a body component for purposes of the requirements.
The NHTSA concludes that parts A, E, and F of paragraph 52 describe joints between maintenance access panels and the bus body. The heater ducts in parts B, C, and D are the type of ventilation space that is not subject to requirements for joint strength.
In response to your question concerning the effect of seat cushion deflection on the location of the seating reference point, the NHTSA has determined that the definition of seating reference point contemplates some deflection of seat cushions to simulate compression of padding material under the weight of a human torso and thigh. As noted in the preamble of the second proposal for a school bus seating standard (39 FR 27585, July 30, 1974), "It can be seen that the manufacturer's freedom to locate the point is sharply restricted by the definition which specifies that it actually simulate the position of the pivot center of the human torso and thigh, following SAE placement procedures." However, since the seating reference point is an approximation of the pivot center, the NHTSA permits the manufacturer to locate the point based upon nominal seat cushion deflection.
SINCERELY,
Ward SCHOOL BUS MFG., INC.
December 7, 1976
Frank Berndt Acting Chief Counsel NATIONAL HIGHWAY TRAFFIC SAFETY ADMIN.
Subject: Interpretation of FMVSS 221, School Bus Body Joint Strength
We have interpreted FMVSS 221 and are currently working on design changes which will enable us to meet this specification in the future. Since there is some latitude for interpretation in the specification, the purpose of this letter is to convey to you exactly our interpretation of FMVSS 221 as it relates to our body design and request that you review the interpretation.
We ask that you reply to each item as to the validity of our interpretation. This review is being requested in order to eliminate the possibility of erroneous designs due to incorrect interpretation of the standard.
We have chosen a format which we feel is concise and will minimize the paperwork involved. The subject joints are numbered consecutively with the first group being those which we have determined must meet FMVSS 221. It should be noted that there are a few compound joints in this group which contain areas which we feel are not required to meet the standard. These situations are noted on the drawings.
The second group is those joints which we have determined as not being required to meet FMVSS 221. Our reasons for the classification are included with this second group. Drawings and photographs have been used to illustrate each joint. The drawings are not necessarily to scale but were drawn in a manner designed to best illustrate the joint configuration. Individual joint drawings and photographs have been numbered to correspond with the joint descriptions contained herein.
If you need any additional descriptive information, please let us know.
We ask that the drawings and photographs be given confidential treatment.
It should be noted that it is our understanding that any components which are completely below the bus floor level or forward of the windshield are not required to meet the provisions of FMVSS 221.
BY OUR INTERPRETATION OF FMVSS 221, THE FOLLOWING JOINTS (NUMBERS 1-34) ARE REQUIRED TO MEET THE 60% JOINT STRENGTH STANDARD.
1. Front cap joint to upper front cowl.
2. Upper front cowl joint to lower front cowl.
3. Rear cap joint to header and rear outside panel.
4. Rear panel (interior and exterior) joints to emergency door frame.
5. Rear exterior panel joint to rear bottom frame.
6. Rear cap inside lining joint to header.
7. Rear inside lining joint to header.
8. Rear interior lining joint to frame bottom channel.
9. Rear emergency door drip trough joint to header and end cap.
10. Rear inside lining joint to bow.
11. Side skirt joint to floor.
12. Skirt section joints.
13. Center skirt section joint to wheel well.
14. Floor section joints.
15. Wheel well joint to floor.
16. Exterior trim panel (immediately adjacent entrance door) joint to bow and side sheet.
17. Interior trim panel (immediately adjacent entrance door) joints to entrance door frame and bow.
18. Interior side sheet joint to rear interior lining and rear frame corner post.
19. Interior sheet joint to exterior side panel and sill.
20. Interior sheet joint to skirt and back-up angle.
21. Interior side sheet overlap and joint to bow.
22. Interior top lining joint to bow.
23. Interior front header lining joint to header.
24. Interior front header lining joint to interior top sheet and bow.
25. Side window header joint to inside and outside lining.
26. Exterior front cap joint to top skin and bow.
27. Top skin joint to top skin and bow.
28. Exterior side sheet joint to skirt.
29. Rear sheet joint to aft edge of exterior side sheet and reinforcing channel.
30. Exterior rear sheet joint to bow.
31. Left front exterior panel---top section joint to bottom section.
32. Left hand exterior panel forward edge joint to front cowl and post.
33. Left front exterior panel to driver window sill.
34. Aft edge of left front exterior panel joint to side sheet and bow.
BY OUR INTERPRETATION OF FMVSS 221, THE FOLLOWING JOINTS (NUMBERS 35-52) ARE NOT REQUIRED TO MEET THE 60% JOINT STRENGTH STANDARD.
35. Lower center skirt section joint to upper center skirt section.
Reason: In view of the joint configuration, the lower section does not act to enclose occupant space. The joint between the upper center skirt section and the floor is required to meet the standard.
36. Exterior bow cover joint to sill, side sheet, and bow.
Reason: This is a small panel which is insignificant in enclosing occupant space. The vertical edges of this panel are also curved around the bow edges and do not present a flat edge.
37. Exterior trim panel at driver's window joint to "Z" bar and bow.
Reason: This is a small panel which is insignificant in enclosing occupant space. The vertical edges of this panel are also curved around the bow edges and do not present a flat edge.
38. Control console area interior side panel joint to front framework.
Reason: This is considered a maintenance access panel because the bus body wiring passes through it and the control console is installed against it.
39. Front cowl leg, left and right hand, joint to front framework and cowl.
Reason: These legs are structural members.
40. Rear turn signal housing joint to rear panel.
Reason: The turn signal housing is not considered a panel and it does not join the rear panel at a panel edge.
41. Front body mounted turn signal housing joint to front cowl.
Reason: The turn signal housing is not considered a panel and it does not join the cowl at a panel edge. Also, these turn signals are optional items which are not installed on every bus.
42. Inside lining joint to outside lining at rear visibility windows.
Reason: The grazing rubber for glass mounting is installed along this joint. The window area is excluded from the 60% requirement in Section S4 of Standard 221. Also this is not a panel edge but rather a hole in the panel. The edges of the panel are required to meet the standard.
43. Shoulder cap (wire cover) joint to interior side sheet and window sill.
Reason: In most cases, bus body wiring is routed inside this cap thus making it a maintenance access panel and excluding it from the joint strength standard. It is understood that in cases where there are no wires beneath the cap, the subject joints are required to meet the 60% joint strength requirement.
44. Exterior side sheet forward end cap joint to side sheet and doorway trim panel.
Reason: As seen in the photo, this is a small piece which provides the transition from the formed body fairing to the flat doorway area and plays no significant role in "enclosing occupant space."
45. Interior "brite-kote" aluminum panel joint to side sheet (no photo available).
Reason: This is an optional decorative item which is furnished on only a limited number of buses.
46. Interior bow cap joint to bow.
Reason: This panel must be removed in order to replace the window, thus it is considered a maintenance access panel.
47. Rear header joints to bow.
Reason: The rear header is a structural member with only a small amount of surface area exposed to the inside of the bus occupant space.
48. Front header joint to upper front cowl and posts.
Reason: The front header is a structural member with only a small amount of surface area exposed to the inside of the bus occupant space.
49. Rub rail joint to side panel.
Reason: These exterior rails do not serve to "enclose occupant space."
50. Plywood floor on standard metal floor.
Reason: This is an optional insulating material.
51. License plate inset panel joint to exterior rear sheet.
Reason: The license plate inset panel is welded into a hole which is cut in the rear body panel, thus the edge of the rear body panel is not included in the joint.
52. Several items located primarily in the forward section of the bus are designed for functional purposes and are thus excluded from the standard. These items include the following (see photographs):
A) Left hand control console;
B) Left hand heater;
C) Heater duct;
D) Right hand heater;
E) Instrument panel;
F) Transmission cover plate.
We believe that these categorized lists illustrate the fact that we have tried to objectively interpret FMVSS 221. Your review of those items and subsequent reply will serve to indicate the accuracy of our interpretation.
Your cooperation is appreciated.
Raymond Titsworth, Project Engineer