Part 6: Building a Stronger Patient Compartment
Apr 29, 2026
This video was originally released in May 2017. Part 6 of 7: This video provides an overview of two crash test methods to make sure the roof is strong enough to handle a rollover, and the floor can support the patient cot. This series, Improving EMS Safety Through Ambulance Design & Testing, covers new crash test methods to improve worker and patient safety in an ambulance patient compartment. It was jointly funded by NIOSH and the Department of Homeland Security's Science and Technology Directorate. NIOSH (DHHS) Pub. No. 2017-143(6)
This video can also be viewed at
https://www.cdc.gov/wcms/video/low-res/niosh/2026/48064806BuildingaStrongerPatientCompartment.mp4
One of the key elements of vehicle crash safety is ensuring the integrity
of the patient compartment during a crash, allowing for a protected space.
In model year 2017, the National Highway Traffic Safety Administration is expanding the requirement
for roof crush to altered and modified vehicles under 10,000 pounds.
This change will include most van-style ambulances.
However, modular ambulances, which are more than 10,000 pounds,
fall outside this regulatory requirement.
To ensure modular-style ambulances are built to manage the impact load from a rollover event,
ambulance manufacturers, in conjunction with government partners, have developed SAE J3057.
In a companion effort, ambulance builders are also working to improve the subfloor strength
so they can be confident the floor substructure has sufficient strength
to manage the new higher loading needed to retain improved patient COT systems.
Their work has resulted in the development of a new test described in SAE J3102
to evaluate floor strength for van and modular ambulances.
This module provides you with the background information
to explain how these tests were developed and how a successful test benefits you and your patient.
SAE J3057 was developed to ensure a safe space
for patient compartment occupants is maintained while still allowing the doors
to be opened after a crash or rollover event.
In the early days of ambulance testing, an ambulance patient compartment was tested
in the same way as a school bus.
One and a half times the weight of the vehicle was applied to the roof
of the patient compartment, and while the roof was still under load, the door still had
to be opened with no permanent deformation.
In 2007, the ambulance manufacturers increased the load to two
and a half times the weight of the vehicle to the roof and to the side of the modular body.
While under load, the doors still have to be able to be opened.
As the industry continued to mature, the partners realized that during an actual rollover,
some damage would occur to the patient compartment, so the new test, SAE J3057,
requires that the patient compartment experience an impact prior to the 2.5 load being applied.
Because we can't roll every ambulance from every manufacturer,
we conducted three different styles of rollover test
and measured the accelerations and forces at impact.
We used this measured data as the basis for the impact loading used in the first phase
of the roof crush test described in SAE J3057.
Using the data from these tests, we developed a two-phase strength assessment
for the patient compartment.
In the first phase, the vehicle is impacted with 28,000 pounds of force
at the roof edge, just as would be seen if the vehicle rolled.
The second phase simulates the vehicle rolling over onto its roof.
To be conservative, a load that equals two and a half times the weight
of the vehicle is applied to the roof.
One way to do this is with a hydraulic press.
To pass this test, roof crush is measured to ensure there's still a survivable space.
After the roof crush, then the doors must be able to be opened so occupants can get out.
If the builder is able to meet this requirement,
the patient compartment passes the testing requirement for SAE J3057.
As part of the research to improve worker and patient safety,
testing was done on the patient cot, cot mount, and restraints.
During this testing, loads were measured under the test floor
so that ambulance builders have the information they need
to better design the subfloor structure.
To ensure all builders have a way to verify that their subfloor structure is strong enough
to manage loads from the new cot and cot mount systems, SAE J3102 was developed.
The SAE J3102 test method provides two different options for testing.
An ambulance builder can either complete a dynamic test where an impact pulse is applied
or the builder can complete static testing.
In a dynamic test, the builder can either use an actual cot with a test dummy
or could use a mass to represent the mount, cot, and patient weights.
Regardless of the loading method, real cot, or simulated weight,
the goal of this test is to ensure that the mass remains attached to the vehicle,
ensuring that the substructure has been able to manage and distribute the loading without failing.
To provide builders with another way to pass this test,
the team also created a static test option.
If a builder wants to install one of the heavier cot systems,
a load approaching 18,000 pounds needs to be applied
to the floor substructure through the load input device.
Regardless of the choice, static or dynamic, SAE J3102 requires the builder to test
in the front, side, and rear directions.
The goal of our work is to make sure EMS workers are as safe on the job as they would be getting
to the job in their own personal vehicle.
One of the ways we've done that is by improving modular body strength
and subfloor strength for both modular and van ambulances.
When purchasing your next ambulance,
we strongly suggest your ambulance purchase specification includes the requirements
of SAE J3057 for modular body integrity and SAE J3102 for subfloor strength.