Can you hear me now?

[ckroll 101]

Can you hear me now?

The use of lights and sirens is a topic that surfaces with regularity, but we seem to let it drop at usage… do we or don’t we. Monty asked a great question in another thread: Can we outrun our sirens? At first blush, it sounds unlikely. We don’t go faster than the speed of sound. On exploration, I found the answer is surprising.

I followed up on his post, and searching ‘siren effective distance and emergency’ found the same source, “Lights and Siren: A review of emergency vehicle warning systems.” at www.naemd.org/articles/warningsystems1.htm that is worth reading.

10 to 15 mph is the recommended safe speed to enter an intersection.

Another, under the title “The Alarming Sounds of Silence” is also a good read.

It comes to the same conclusion.

The information is old, but the physics hasn’t changed. Sound pressure drops off as a square of distance from its source [as does light]. It is diminished [attenuated] as it passes through objects. The sound threshold is the range where a sound is audible up to where it inflicts pain. For this reason sirens are usually restricted to 118 dB at 30 feet. [to protect the user]. To be detectable, sound needs to be 8 to 12 dB above ambient noise which in an otherwise quiet car [70 dB] with windows rolled up is about 78 dB. A screaming child is 90 dB [ I know, we all thought it was more than that.], so close to 100 dB is needed for detection of a siren.

The math that falls out of this is that, best case, sirens will only be effective [inside a quiet, closed car] up to 30 to 50 meters [90 to 150 feet]. If it is a well insulated car or the kids in the back seat don’t like the movie, it will be less than that.

Assume a driver in a closed car with no distractions hears a siren when it is 150 feet away. Perception/Reaction time to unexpected events is roughly 1.5 seconds.

[ So if the vehicle with the siren is closing on a common point with another vehicle at a speed of 100 feet per second, then the vehicles collide at the moment the second driver reacts to the emergency. That is definitely outrunning the sirens.]

If one assumes that a total of 5 seconds is necessary to perceive [1.5 secs] and to execute [3.5 secs] a ‘see and avoid’ maneuver, then the maximum closing speed over 150 feet, [if the collision is to be avoided] can only average 30 feet per second. That’s 20 mph. Other braking distance models put the initial speed closer to 30 mph. Wow. Anything faster than that as a differential speed between a closed car and a siren may technically be outrunning the ability of sirens to inform the general public of our approach in time for them to take meaningful evasive action.

Assume any distractions, assume a little weather, assume there’s noise in the vehicle, assume an older driver, or one eating lunch, and all of a sudden a maximum entry speed into an intersection of 10 to 15 mph sounds reasonable, and a full stop sounds even better. Thanks, Monty, for bringing it up. Does anyone have any better numbers on the subject?

.

[Guest WolfEMT]

I'm sure the same premise applies to sirens as it does for headlights; for instance, if you're driving on a dark road and you're going too fast, it is possible to overdrive your headlights, so I'm sure that it's possible to overdrive the sonic waves produced by the siren box.

And, with newer cars comes increased technology in terms of sound deadening. You could be approaching a brand new, high-end car and the occupants, especially if they have the windows up and radio on, might not hear you.

[SRS131EMTFF 471]

Giving Cars the Silent Treatment - Car News

The Daily Auto Insider

Wednesday, March 28, 2007

March 2007

Car companies, including General Motors, Hyundai and Ford, are competing to minimize noise by using new materials, new manufacturing techniques and modifying exterior and interior design, The Wall Street Journal reported.

Among the silencing strategies: GM's Buick is using laminated-glass windows on a forthcoming model; Ford makes parts, such as dashboards and engine-oil pans, of a vibration-absorbing metal-plastic composite it calls “quiet steel;” and Hyundai is using electronically adjustable engine mounts and extra-thick, lightweight foam insulation on its new Veracruz sport-utility vehicle to minimize engine noise, the story said.

By making cars quieter, automakers hope to attract buyers who generally view a silent interior as a sign of high quality.

They haven't succeeded entirely, however. David Green, an automotive product analyst with J.D. Power & Associates, told the WSJ that the research company has seen a 36 percent decrease in wind-noise complaints since 2003 from drivers responding to its initial quality survey, which measures owner satisfaction 90 days after buying a car. In the same period, however, the decrease in wind-noise complaints was 7 percent in the company's longer-term vehicle dependability study, indicating that after three years of ownership wind noise is still present and problematic.

http://www.caranddriver.com/carnews/12733/...-treatment.html

[Guest]

Among the silencing strategies: GM's Buick is using laminated-glass windows on a forthcoming model; Ford makes parts, such as dashboards and engine-oil pans, of a vibration-absorbing metal-plastic composite it calls “quiet steel;” and Hyundai is using electronically adjustable engine mounts and extra-thick, lightweight foam insulation on its new Veracruz sport-utility vehicle to minimize engine noise, the story said.

Correct me if I am wrong, but doesn't that mean that our trusty window punches will no longer work on these windows?

[ny10570 745]

ckroll, great post. Thanks for the simple breakdown.

Several European auto-makers have used laminated glass in their cars over the past few years. It sucks for us. On the upside since they're not glued around all 4 sides like windshields they are easier to take out, it just requires a little more violence. Be careful.

Edited August 5, 2007 by ny10570

[Oswegowind 17]

I am guilty of being a car driver...However warning devices as intended do not always work properly or perfectly. I think that people have to take this into consideration when driving emergency vehicles, that just maybe the other persons do not see nor hear you. I mean we have all been there, especially in NYC when you hear the sirens coming but cannot place the direction cause the waves are bouncing off of buildings and you cannot see the reason for the sirens immediately. Where is it coming from? You look back and see nothing, front and see nothing and then all of a sudden here they come from a side street and you have a moment to react because visibility is so impaired by your surroundings. Hopefully if they have a red light they are stopping to make sure you are clear and not just taking for granted that you heard them and saw them when you really didn't. If I am in the path of a responding apparatus, I move over to the right a far as I can, even when they are coming in the opposite direction cause someone may not see them and they will have to swerve which if I didn't move they will hit me. However, if I am at an intersection and they go across, am I supposed to move out of their way if they are not traveling in the same direction as me? I mean N&S or E&W. I just think that everyone who drives an emergency vehicle should not ASSUME that the other drivers are going to do what they are supposed to do. Don't take it for granted (lol) that Mrs. Smith is looking both ways while going through an intersection in which she has the green light. Not worth it one bit. Just think of all the paperwork you will have to do, the questions you will have to answer day in and day out. It may have been a moment but it can be a lifetime's worth of bs that you have to deal with!

[wcr20 17]

I love this thread - the points made are all top notch. Thers's an old aying that no one ever lost money betting on the stupidity of others (or something like that) - and I think it applies here. Drive (always) like the other guy is going to do the worst thing possible at the worst moment possible, doesn't matter if you're operating a car, ambulance, fire apparatus, motor cycle, or a riding mover.

People drive with their Ipod in one ear, their phone in the other, a Big Mac in one hand... well, you get the point. Do not count on them hearing or seeing you, whether you have 1 or 4 sirens, and more lights than the ship in Close Encounters, or on them taking the correct action if they do happen to break out of their fog.

But, we've all hear all of this before, so I'll quit now....

[RescueKujo 130]

And, with newer cars comes increased technology in terms of sound deadening. You could be approaching a brand new, high-end car and the occupants, especially if they have the windows up and radio on, might not hear you.

I remember a Ford commercial expounding the virtues of the quietness of the F150. With the camera outside the truck, they're using a Federal Q and airhorns, then the camera is inside and you hear absolutely nothing. It made me wonder if any of the automaker's engineers had thought about the driver and passengers hearing emergency vehicles.

[Remember585 815]

It made me wonder if any of the automaker's engineers had thought about the driver and passengers hearing emergency vehicles.

They don't care about that. They are trying to market their products to people that want reduced road noise. It's not a fact that anyone should be proud of, but the plain and simple is this - WE HAVE TO LEARN HOW TO OPERATE OUR EMERGENCY VEHICLES AS IF EVERYONE IS DEAF, BLIND and possibly DUMB.

Always assume the worst. Pre-plan your response, size-up your road and traffic conditions, anticipate your turns, moves and obstacles and consider if using your warning devices is truly neccessary.

Relocating to another firehouse for a cover assignment - no need for warning devices.

Lift assist with no reported injuries - no need for warning devices.

ETC., ETC., ETC.

I know people are going to argue with me, but it's how I feel. Our FD has "Non-emergency" responses for CO Calls with no symptoms, elevator rescues, fluid spills, and a few other calls. Plus, many, almost most of our calls, a Chief or an IC will knock everyone down to the non-emergency response and/or return units that are not needed. One example is AFA's - we generally hold the Truck and Rescue and send the Engine non-emergency mode to investigate and handle paperwork.

And, to be honest, I don't see a significant amount of time saved or lost based on how we respond. If anyone can prove otherwise, let me know.

[Guest]

i read somewhere that electronic sirens cannot penetrate newer high end cars like a Lexus, BMW, Benz. BUT, mechanical sirens (the Q siren) CAN still penetrate these cars, even at a safe distance. i will try to find the article...the differences are in the sound waves themselves. electronic sirens are shot out of the speaker, going wild and at the mercy of wind. the mechanical siren is more effective because the sound waves travel faster and more controlled, due to the tight spinning pattern.

if you know guns, put it this way.

electric siren is like a shotgun , w/ a modified choke. the pellet pattern just sprays after a certain distance

the mechanical siren is more like a rifle or shotgun slug. the bullet or slug it doesn't spray. its just a spinning straight shot.

(hope that helped)

[ckroll 101]

i read somewhere that electronic sirens cannot penetrate newer high end cars like a Lexus, BMW, Benz. BUT, mechanical sirens (the Q siren) CAN still penetrate these cars, even at a safe distance. i will try to find the article...the differences are in the sound waves themselves. electronic sirens are shot out of the speaker, going wild and at the mercy of wind. the mechanical siren is more effective because the sound waves travel faster and more controlled, due to the tight spinning pattern.

if you know guns, put it this way.

electric siren is like a shotgun , w/ a modified choke. the pellet pattern just sprays after a certain distance

the mechanical siren is more like a rifle or shotgun slug. the bullet or slug it doesn't spray. its just a spinning straight shot.

(hope that helped)

I searched " mechanical electronic siren compare" and found your source at timberwolfsirens. It is written by the manufacturer of mechanical sirens and has a bias towards them. The physics is dumbed down to the point of being misleading. The speed of sound and attenuation are constants. Different frequencies will have different characteristics, as will speakers. Yes, a siren will sound different in a football field than it does in the canyons of Manhattan. That said, what matters is performance.

The points about bounce off hard surfaces and directionality are well taken. Not so much the comments about outrunning sirens, at least in practice. In a straight line coming at someone is how they measure these things. In that situation your lights will be doing more for you than the siren ever will. Sirens are there because sound gets around corners and light does not, but it does so at great loss. Performance at intersections is not measured or mentioned, in part because there are so many variables, the test wouldn't mean much.

All these devices are designed and measured for getting the person directly in front of you to turn around and get out of the way. They are NOT designed to protect your flanks from orthogonal crossfire.

Taking the gun analogy....If you only fire your gun straight ahead [sirens in a grille],-- whether it be rifle or shotgun-- you are still going to get smacked up the left side of your head by the dude with the base ball bat standing next to you.

So lets do some experiments. Can anyone out there get some measuring equipment and we can test how well sirens work around corners with closed cars????? Maybe we can come up with something that will improve intersection safety.

[Guest bibbles10504]

I wonder if the new siren Federal came out with... the Rumbler would effect these calculations??

http://www.fedsig.com/products/index.php?id=253

[E1E2TL3 0]

All these devices are designed and measured for getting the person directly in front of you to turn around and get out of the way. They are NOT designed to protect your flanks from orthogonal crossfire.

Taking the gun analogy....If you only fire your gun straight ahead [sirens in a grille],-- whether it be rifle or shotgun-- you are still going to get smacked up the left side of your head by the dude with the base ball bat standing next to you.

Gotta love the analogies. This is very true. And lets not forget about driveways and parking lots.

[Goose 188]

I give a gold star to everyone that pulls over for me before they see my pretty lights in their rearview. There has got to be a product out there that will help give an audible warning in a more spherical pattern, no?

[Guest partyrock]

In every vehicle all the audible warning devices are pointed straight ahead has anyone tried mounting them at a an angle to improve the ability of the sound to get around corners. Or maybe that wouldn't result in a significant difference.

[ex-commish 490]

They don't care about that. They are trying to market their products to people that want reduced road noise. It's not a fact that anyone should be proud of, but the plain and simple is this - WE HAVE TO LEARN HOW TO OPERATE OUR EMERGENCY VEHICLES AS IF EVERYONE IS DEAF, BLIND and possibly DUMB.

Always assume the worst. Pre-plan your response, size-up your road and traffic conditions, anticipate your turns, moves and obstacles and consider if using your warning devices is truly neccessary.

Relocating to another firehouse for a cover assignment - no need for warning devices.

Lift assist with no reported injuries - no need for warning devices.

ETC., ETC., ETC.

I know people are going to argue with me, but it's how I feel. Our FD has "Non-emergency" responses for CO Calls with no symptoms, elevator rescues, fluid spills, and a few other calls. Plus, many, almost most of our calls, a Chief or an IC will knock everyone down to the non-emergency response and/or return units that are not needed. One example is AFA's - we generally hold the Truck and Rescue and send the Engine non-emergency mode to investigate and handle paperwork.

And, to be honest, I don't see a significant amount of time saved or lost based on how we respond. If anyone can prove otherwise, let me know.

You must of been one of my EVOC students... ....I preach the very same thing when I conduct a class. Many of our calls do not warrant the lights and sirens especially relocating to another house for a standby. I even feel if you are called to the scene hours later is the noise necessary?

Remember..wether you are driving or directing traffic....the other drivers do not care about you !!!

[Union241 3]

I wonder if the new siren Federal came out with... the Rumbler would effect these calculations??

http://www.fedsig.com/products/index.php?id=253

It seems to me that the Rumbler is designed for approaching major intersections and isn't intended to be used as a regular warning device like an electric siren or a Q. With it's 10 second timer it seems to me that if one were to be using it, even to complement another siren, that one would still run into the same issue of out running it. The pulses are going to be stronger the closer you get to a car, but when you figure the amount of time that it would take a driver to notice the vibrating sensation from it and then the 1.5 seconds it takes for them to react to the approaching apparatus, you'd almost practiacally already be on top of the car and you're just experiencing the same issue as if you didn't have it at all. It does seem that it would be a good product to have when you're at a major intersection with multiple lanes in either direction where the apparatus is slowing down to 10-15 MPH and where it would have more of an impact with the increased time that the other drivers would have to notice it and even if another driver's view is blocked by another vehicle it would give them more of a warning that something is up and get them looking.

[Monty 35]

Thanks ckroll for running with this. Glad to see that I wasn't completely bonkers with my thinking. Interestingly this week I was on an interstate and coming the other way was an ambulance. I'm guessing our combined closing speed was approximately 150mph, I saw the lights first, and heard the siren for all of 2 seconds - maybe.

It seems there have been some attempts to find alternatives to the current lights and sirens, although I don't think they have been too successful. I remember reading somewhere about this topic - but of course can't find it now! I did find a couple of things: Emergency Warning Radio Transmitter - interesting little disclaimer at the bottom of this page. Basically it seems you can't legally buy this thing in the US! Here's another idea, but this is from 1996 - so obviously not a commercial success ...

Transmitter for Radar Detector .

On the sub-thread of when to respond (or not) with L&S, I agree that there's too much equipment responding L&S. However, in certain areas I don't see this changing any time soon. Without getting in to the whole home rule discussion, I see this needing to be supported from something like the County Chiefs - maybe writing standards in to mutal aid agreeements. Maybe setting standards for what 'Respond with Caution' means might be a start.

[ckroll 101]

Thanks ckroll for running with this. Glad to see that I wasn't completely bonkers with my thinking. Interestingly this week I was on an interstate and coming the other way was an ambulance. I'm guessing our combined closing speed was approximately 150mph, I saw the lights first, and heard the siren for all of 2 seconds - maybe.

It seems there have been some attempts to find alternatives to the current lights and sirens, although I don't think they have been too successful. I remember reading somewhere about this topic - but of course can't find it now! I did find a couple of things: Emergency Warning Radio Transmitter - interesting little disclaimer at the bottom of this page. Basically it seems you can't legally buy this thing in the US! Here's another idea, but this is from 1996 - so obviously not a commercial success ...

Transmitter for Radar Detector .

On the sub-thread of when to respond (or not) with L&S, I agree that there's too much equipment responding L&S. However, in certain areas I don't see this changing any time soon. Without getting in to the whole home rule discussion, I see this needing to be supported from something like the County Chiefs - maybe writing standards in to mutal aid agreeements. Maybe setting standards for what 'Respond with Caution' means might be a start.

You asked a good question. I also was out and about without my pager on today and, in a closed car with no radio thought I heard something. I was stopped at a red light and it was 5 seconds later the ambulance crossed. [At about 20, with the passenger watching for cross traffic. [Well done Putnam Valley.] 5 seconds at 20 mph is in line with the physics.

I think chasing the goal of defeating insulation as car makers continue to make it harder to crack the nut is not going to be a winning strategy. Given the remarkable advances in technology, On Star, GPS, EZ Pass, and avionics standard in IFR rated airplanes, I'm thinking that ES vehicles ought to transmit a signal that could be received by a unit mounted inside a car that sets off a light on the dashboard telling the driver to look up and look out there is an emergency vehicle closing in.

When the collision avoidance monitor lights up in the plane, small as it is, it really gets your attention. [ Glitch in the system, it occasionally 'self reads', pilot knows better but it scares the stuffing out of me. The little planes overlap and the screen turns orange, telling you that you have about 2 seconds to live...] No trees or buildings up there, but maybe the technology could be applied at reasonable cost. That still does not address the worst case of a poor driver not paying attention. I think focus ought to be on educating ES drivers to keep it safe, after all, we KNOW when there's going to be an ES vehicle running a red, the other guy doesn't.

I smell an invention.......