Is there a weight limit on standard car seats?

Question

Is there an advisable weight limit for an adult, using a standard car seat. If a person was over that weight, what would be the likely consequences in a collision?

Answer 1

Its not the seat, but the air bag and seatbelt thats the factor for weight in an accident.

The seat has no limit (although it may wear out or break with excessive weight)

But the Air bag and Seatbelt (including pre-tensioner) has a limit to the weight it can take.

Do you have a car in mind? We will need all the info to give you a definite answer - MAKE, MODEL, YEAR etc.....

Its a Physics question - conservation of momentum - the heavier you are, the more momentum you will carry forward. The belt will act more on your body and the same goes for the airbag.

The heavier you are, the greater the forces acting (and hence more bodily damage).

Answer 2

For small- and large-stature adults, airbags may do more harm than good, new research indicates.

A look at 11 years of crash data involving 65,000 front-seat passengers found that while airbags are "modestly" protective for people of medium stature (5 feet 3 inches to 5 feet 11 inches), they appear to increase the risk of injury to people smaller than 4 feet 11 inches and taller than 6 feet 3 inches.

Dr. Craig Newgard of Oregon Health and Science University in Portland reported the findings yesterday at the Society for Academic Emergency Medicine meeting in Chicago.

Among 52,552 drivers and 14,732 front-seat passengers involved in motor vehicle crashes over the 11-year study period, 2.5 percent of drivers and 2.6 percent of passengers were seriously injured.

The data suggest, Newgard said, that "both small-stature and large-stature occupants look to be at increased risk of injury from the airbag rather than having a benefit."

Body weight was not a contributing factor to injury rates. This is a potentially important observation, given that many "smart" airbags use body weight to determine how the airbag deploys.

Answer 3

All seat structures and belt systems for modern passenger cars are tested to specific regulations.

They are tested at 30mph using dummies weighing around 105kg.  This tests the integrity of both the safety belt system and the seat/vehicle body structure.  These tests must be passed for the vehicle to be sold.

In addition to this the seat and belt system are tested independently in both static and dynamic tests.  they are subjected to high loads over a long period of time as well as being aged before testing to simulate older vehicles.

Modern vehicles are usually tested with both 5%ile (around 4'11" & 55kg) and 50%ile (around 5'8" & 85kg) occupants in frontal impacts.  As of yet there are no legislations for larger occupants, although it has been suggested by the head of EuroNCAP as being implemented in the future.

In a collision a heavy person would have more inertia so would experience higher forces on their body, however in modern vehicles the seatbelt system and airbag are designed to operate together to help protect the occupant.

If the occupant is not wearing a seatbelt the airbag will have to do more work and may not prevent injuries to the same extent as if the occupant was wearing a seatbelt. So the weight of the occupant is not as significant in an impact when compared to whether or not they are wearing a seatbelt.

Modern seatbelts are normally made from woven nylon so they stretch, even after the pretensioners fire.  This is designed to reduce the risk of injuring the occupant by restraining them.  Most modern belt systems also use a load limiting system to further reduce the risk of injury caused by the belt system.

UCANTCME's reference to the studies made in America raises an interesting point though.  Considering that there are many states where it is not a legal requirement to wear a seatbelt, and the fact that airbag technology has been developing rapidly over the period of time mentioned, it may not actually be a valid study of system performance.  Including the fact that there is no mention of how the serious injuries occured (lower leg injuries caused by vehicle deformation are often far more serious than injuries inflicted by airbags) makes this data questionable in my opinion.

The sensors that use body weight to "sense" occupants are no longer used in modern vehicles.  They have been replaced by sensors that check seat position (fore/aft in the vehicle). They are used to protect smaller occupants from being injured by the airbag by only firing 70% of the airbag's possible detonation charge.  The remaining 30% is fired 100ms after the first charge so the vehicle is safe for rescue workers to work on.  This time interval is designed to allow the occupant to rebound from the bag so the second detonation causes no damage.

However, all airbag systems rely on the occupant being seated correctly in the vehicle.  If the occupant is too close to the airbag when it detonates (approx 30cm or 12") then they are likely to be injured by the deployment on the bag.

As people who are heavier are also often larger physically this can produce a higher risk of personal injury for a larger/heavier person depending on how close they are to the airbag when it detonates.

Answer 4

I agree. The seat is rated for something like 350lbs. The seat belt and airbag system can only take so much, and weight doesn't have much to do with that, speed does. The simple formula is double the weight, double the amount of energy to stop you, double the speed, 4 times the amount of energy to stop you.