1 00:00:00,000 --> 00:00:01,840 Before we get started I want to let you know that   2 00:00:01,840 --> 00:00:05,360 I will not be setting any of the alarms off in this video. 3 00:00:06,080 --> 00:00:08,492 When you last went shopping for smoke detectors, 4 00:00:08,799 --> 00:00:13,971 did you notice that there were two different detection technologies available to put your dollars towards? 5 00:00:13,971 --> 00:00:17,966 Let me tell ya, even though I shop for smoke alarms every other Wednesday 6 00:00:17,966 --> 00:00:19,296 it hadn’t occurred to me. 7 00:00:20,141 --> 00:00:23,138 That’s a lie, this is just a silly setup. 8 00:00:23,138 --> 00:00:26,499 In fact I only rarely go shopping for smoke detectors, 9 00:00:26,499 --> 00:00:29,905 but the last time I did was to replace one of mine because 10 00:00:29,905 --> 00:00:32,000 SOMEbody had installed the wrong type! 11 00:00:32,800 --> 00:00:34,537 The wrong type? 12 00:00:34,537 --> 00:00:37,172 There’s a wrong type of smoke detector? 13 00:00:38,017 --> 00:00:41,363 Well… suboptimal might be a better word. 14 00:00:41,363 --> 00:00:45,725 See, the detector outside my  bedroom is in a hallway that leads to the kitchen. 15 00:00:45,725 --> 00:00:50,011 And it’s right next to a return vent for the  building’s HVAC system. 16 00:00:50,011 --> 00:00:56,919 That’s not ideal from the start but it’s hardwired and interconnected to the other alarms here so moving it isn’t an option. 17 00:00:56,919 --> 00:01:02,321 Anyway, being almost in the kitchen and having  kitchen air pulled near to it, 18 00:01:02,321 --> 00:01:06,419 I was getting nuisance alarms every time I made toast. 19 00:01:06,419 --> 00:01:07,982 And I am not exaggerating. 20 00:01:07,982 --> 00:01:08,791 Every. 21 00:01:08,791 --> 00:01:09,710 Single. 22 00:01:09,710 --> 00:01:10,210 Time. 23 00:01:10,560 --> 00:01:13,831 And often when I dared to simply use the oven! 24 00:01:13,831 --> 00:01:16,606 Didn’t even matter if I had put something in it yet. 25 00:01:16,606 --> 00:01:17,975 What was going on? 26 00:01:17,975 --> 00:01:19,791 Well, that smoke alarm 27 00:01:19,791 --> 00:01:21,392 (which is now right here) 28 00:01:21,392 --> 00:01:26,555 used the good old fashioned ionization chamber for its smoke  detection abilities. 29 00:01:26,555 --> 00:01:28,496 It’s slightly radioactive! 30 00:01:29,120 --> 00:01:32,160 Now that’s a tried and true method for detecting smoke, 31 00:01:32,160 --> 00:01:35,622 in fact in some cases it works a little too well, 32 00:01:35,622 --> 00:01:42,088 uh but these days it’s revealing its weaknesses and according to some these should be considered obsolete. 33 00:01:42,088 --> 00:01:48,000 I replaced it with a photoelectric smoke detector and  not only have the nuisance alarms completely stopped 34 00:01:48,000 --> 00:01:52,988 but I will probably have more advanced warning of a fire should one happen. 35 00:01:52,988 --> 00:01:55,847 At least, depending on the fire. 36 00:01:56,160 --> 00:01:58,327 Ah! A nuanced discussion! 37 00:01:58,327 --> 00:02:01,071 Those go great with the internet. 38 00:02:01,071 --> 00:02:06,407 Let me start out by saying that regardless of what smoke alarms you might have in your home 39 00:02:06,407 --> 00:02:12,119 the most important thing is that you have them and that you know they are functional. 40 00:02:12,119 --> 00:02:15,469 If you can’t remember the last time you checked your smoke alarms, 41 00:02:15,469 --> 00:02:17,155 do it right now. 42 00:02:17,155 --> 00:02:20,900 Seriously, pause the video, make sure you have them, 43 00:02:20,900 --> 00:02:26,072 and if you’re able to test them without setting  off a central monitoring system, do it. 44 00:02:26,072 --> 00:02:32,857 Most every fire-related tragedy we hear about these days  stems from a home without working smoke alarms, 45 00:02:32,857 --> 00:02:37,636 meaning those tragedies were almost certainly preventable, and all too easily. 46 00:02:37,636 --> 00:02:40,372 You should have a smoke alarm in every bedroom, 47 00:02:40,372 --> 00:02:44,492 in locations immediately outside of sleeping areas such as hallways, 48 00:02:44,492 --> 00:02:49,252 and in addition to that there should be  at least one on every level of your home. 49 00:02:49,252 --> 00:02:54,000 Consult your local fire authority for more specific  recommendations and requirements in your area. 50 00:02:54,800 --> 00:02:57,006 Let’s start with a bit of history. 51 00:02:57,006 --> 00:02:59,780 Smoke detectors are a fairly recent invention 52 00:02:59,780 --> 00:03:04,240 and the household smoke alarm didn’t hit meaningful mass production until the 1970’s. 53 00:03:04,800 --> 00:03:09,132 We needed to clear two hurdles before the smoke  alarm would be commonplace: 54 00:03:09,132 --> 00:03:14,179 First, a reliable and relatively cheap smoke sensor needed to be devised. 55 00:03:14,179 --> 00:03:19,701 And secondly, we’d need to figure out how to make some cheap and mass-producible electronics 56 00:03:19,701 --> 00:03:24,319 which could monitor that sensor and sound an alarm if smoke was detected. 57 00:03:24,319 --> 00:03:30,984 As it happens, the principle on which these first smoke sensors operate was discovered by accident in the 1930’s 58 00:03:30,984 --> 00:03:33,527 by Swiss physicist Walter Jaeger. 59 00:03:33,527 --> 00:03:39,695 He was trying to invent something which could detect  poison gas, which didn’t work. 60 00:03:39,695 --> 00:03:45,758 But his device did react to the smoke particles coming from his lit frustration cigarette. 61 00:03:45,758 --> 00:03:47,440 Or so goes the story. 62 00:03:48,080 --> 00:03:53,591 The sensor used in the first commercial smoke alarms — and plenty that are still produced today — 63 00:03:53,591 --> 00:03:57,781 operates on the same principle as Jaeger’s experimental device. 64 00:03:57,781 --> 00:04:01,031 It is made of a pair of electrodes that span an air gap, 65 00:04:01,031 --> 00:04:07,188 and sitting below a hole in one of the electrodes is a teensy little bit of americium-241 66 00:04:07,188 --> 00:04:10,480 which emits alpha particles by way of being, ya know, 67 00:04:10,480 --> 00:04:11,970 radioactive. 68 00:04:11,970 --> 00:04:15,583 As the americium decays and flings out those particles, 69 00:04:15,583 --> 00:04:19,748 they collide with the nitrogen and oxygen  atoms that make up the bulk of air 70 00:04:19,748 --> 00:04:22,687 and knock loose some of their electrons. 71 00:04:22,687 --> 00:04:26,810 This results in some charged gas molecules between the two plates. 72 00:04:26,810 --> 00:04:33,177 And with the help of a power source to maintain a voltage potential between the plates, often a 9-volt battery, 73 00:04:33,177 --> 00:04:37,105 those now charged molecules become attracted to the electrodes, 74 00:04:37,105 --> 00:04:41,918 and the end result once they move towards them is a lil’ bit of current flow. 75 00:04:41,918 --> 00:04:46,310 And I do mean a lil’ bit, about 100 picoamps. 76 00:04:46,720 --> 00:04:51,120 However, when something’s burning and  releasing smoke particles into the air,   77 00:04:51,680 --> 00:04:54,907 once those smoke particles get between the two electrodes, 78 00:04:54,907 --> 00:05:00,238 they start absorbing or blocking the alpha particles coming from the americium. 79 00:05:00,238 --> 00:05:04,240 That prevents the ionization of the nitrogen and oxygen molecules, 80 00:05:04,240 --> 00:05:07,547 which stops the flow of current between the plates. 81 00:05:07,547 --> 00:05:13,746 A relatively simple electronic circuit can monitor for current flow and sound an alarm if it stops, 82 00:05:13,746 --> 00:05:18,014 and with the development of the MOSFET and its cheapening in the 1970’s, 83 00:05:18,014 --> 00:05:23,840 suddenly we had everything we needed to produce an inexpensive, automatic device for warning of the presence of smoke. 84 00:05:24,720 --> 00:05:31,576 Now, if you’re anything like me, you might think  that resorting to radioactive isotopes seems... 85 00:05:31,576 --> 00:05:33,278 a bit much. 86 00:05:33,278 --> 00:05:37,327 It’s not dangerous or anything,  alpha particles are easily stopped - 87 00:05:37,327 --> 00:05:41,156 the radiation can’t even get through the plastic shell of the alarm. 88 00:05:41,156 --> 00:05:44,800 But, it still feels like a rather… 89 00:05:44,800 --> 00:05:46,638 exotic technique. 90 00:05:46,638 --> 00:05:50,677 After all, we can see smoke particles with our eyes. 91 00:05:50,677 --> 00:05:52,926 And our eyes work because of light. 92 00:05:52,926 --> 00:05:56,686 And since we can see smoke using our light-sensing eyes, 93 00:05:56,686 --> 00:06:01,336 there’s probably a way to use a light sensor to detect smoke. 94 00:06:01,336 --> 00:06:02,537 Indeed there is. 95 00:06:02,537 --> 00:06:10,053 All the way back in 1972, Donald F. Steele and Robert B. Enemark devised an optical smoke detector, 96 00:06:10,053 --> 00:06:15,610 which worked using essentially the same principle  as modern-day photoelectric smoke detectors. 97 00:06:16,000 --> 00:06:21,840 Their idea was to put a light source and two  light sensing photocells in a detection chamber   98 00:06:21,840 --> 00:06:26,800 which would allow air to freely move through  it, but which contained a series of light traps   99 00:06:26,800 --> 00:06:29,597 to prevent ambient light from getting in. 100 00:06:29,597 --> 00:06:36,161 FYI, photocells weren’t by any means a new thing at this point - this wasn’t groundbreaking tech, 101 00:06:36,161 --> 00:06:37,833 just a clever idea. 102 00:06:37,833 --> 00:06:43,144 Anyway, the sensors were arranged so that only one of them could “see” the light source. 103 00:06:43,144 --> 00:06:49,363 The second sensor had no line of sight to the light source, with a series of light-blocking vanes in the way. 104 00:06:49,363 --> 00:06:51,992 When smoke particles entered the chamber, though, 105 00:06:51,992 --> 00:06:57,877 light from the light source would reflect off those particles in every which way and become scattered. 106 00:06:57,877 --> 00:07:00,901 Think of it like a laser beam in a smoky room. 107 00:07:00,901 --> 00:07:04,633 The second sensor could now “see” the light coming from the light source, 108 00:07:04,633 --> 00:07:07,840 thus smoke was detected, and an alarm is sounded. 109 00:07:08,560 --> 00:07:15,659 These early photoelectric alarms used two sensors  as a means of testing the functionality of the light source. 110 00:07:15,659 --> 00:07:21,593 If no light was detected in the first sensor,  this would indicate that the light source had failed. 111 00:07:21,593 --> 00:07:26,128 Which was pretty likely as the early designs used incandescent lamps. 112 00:07:26,128 --> 00:07:27,120 And no, 113 00:07:27,120 --> 00:07:33,549 they were not battery-powered, which is likely a reason  the ionization sensor was preferred for so long.   114 00:07:34,000 --> 00:07:39,027 These days, though, a much simpler and way less  power-hungry arrangement 115 00:07:39,027 --> 00:07:43,546 of infrared LED and single photodetector is used. 116 00:07:43,546 --> 00:07:48,656 The photodetector is positioned in the detection chamber so that it can’t see the LED, 117 00:07:48,656 --> 00:07:52,635 and every few seconds the detector will put out a little  blip of light. 118 00:07:52,635 --> 00:07:59,416 It may also blip a visible LED on the exterior to give indication that it’s powered on and functional. 119 00:07:59,416 --> 00:08:04,541 If it can't see the blip in the photodetector, then the air must be clean. 120 00:08:04,541 --> 00:08:11,840 If, however, the chamber has smoke in it, the smoke particles will scatter the light and some will be picked up by the photodetector. 121 00:08:12,480 --> 00:08:15,231 That usually won’t trigger an alarm right away, though. 122 00:08:15,231 --> 00:08:22,080 Modern designs are often programmed upon first detection to begin an additional and more frequent series of blips 123 00:08:22,080 --> 00:08:24,269 to guard against false alarms. 124 00:08:24,269 --> 00:08:27,840 If, for instance, a piece of dust happened to float into the chamber, 125 00:08:28,400 --> 00:08:31,891 well you wouldn’t want the alarm to go off just for that.   126 00:08:31,891 --> 00:08:39,054 So it will perform a routine where it checks a  few more times in rapid succession for scattered light. 127 00:08:39,054 --> 00:08:46,517 It may also be looking for an increasing signal amplitude and thus thicker smoke over time before committing to an alarm condition, 128 00:08:46,517 --> 00:08:49,050 though that’s speculation on my part. 129 00:08:49,050 --> 00:08:53,908 In any case, if it keeps seeing light hit the photocell after  a pre-programmed test period, 130 00:08:53,908 --> 00:08:55,767 it will sound the alarm. 131 00:08:56,160 --> 00:09:02,000 So, we have two commonly-produced and easily  obtainable smoke detection technologies at hand:   132 00:09:02,560 --> 00:09:08,000 one using commodity LEDs, photodetectors,  a bit of electronics and some plastic,   133 00:09:08,000 --> 00:09:12,961 and the other using some  plastic, a bit of electronics, a couple of metal plates, and 134 00:09:12,961 --> 00:09:16,167 an exotic synthetic radioisotope of americium. 135 00:09:18,000 --> 00:09:20,212 Why are we still making this second kin- 136 00:09:20,212 --> 00:09:21,252 [exasperation noises] 137 00:09:21,252 --> 00:09:24,868 That’s a good question, but before I move on to the pros and cons here, 138 00:09:24,868 --> 00:09:30,455 I want to share that the principle of optical smoke detection is as flexible as it is simple. 139 00:09:30,455 --> 00:09:33,720 While spot-sensing smoke alarms work as I’ve described, 140 00:09:33,720 --> 00:09:40,550 another option is to shine a beam of light across a large distance and measure its received intensity. 141 00:09:40,550 --> 00:09:45,963 You can modulate that beam in some way to allow a sensor to pick up a signal through ambient light, 142 00:09:45,963 --> 00:09:51,920 and a sudden dropout of that modulated signal or  simple intensity loss can indicate smoke. 143 00:09:52,880 --> 00:09:57,339 These are often used in buildings with large open spaces like atria, 144 00:09:57,339 --> 00:10:03,128 and in such buildings you might have seen a funny-looking device at one end of a ceiling pointing across the building 145 00:10:03,128 --> 00:10:06,661 to another one on the other end, or perhaps a retroreflector. 146 00:10:06,661 --> 00:10:13,264 There’s a pretty good chance that was, in fact, a smoke sensor incorporated into the building’s fire alarm system. 147 00:10:13,520 --> 00:10:16,617 Alright, with two very different detection methods, 148 00:10:16,617 --> 00:10:22,541 it’s probably no surprise that the two technologies respond  differently to different kinds of smoke.   149 00:10:23,120 --> 00:10:28,158 This may in part explain why ionization alarms are still on the market - 150 00:10:28,158 --> 00:10:32,831 remember how this one was sensing smoke whenever I made toast? 151 00:10:32,831 --> 00:10:36,365 Toastmaking is really just slightly burning bread, 152 00:10:36,365 --> 00:10:43,482 and even though I don’t like my toast all that dark, little  whisps of smoke are produced as the surface of the bread gets singed. 153 00:10:43,482 --> 00:10:47,237 These smoke particles are really, really small though. 154 00:10:47,237 --> 00:10:50,292 So small that they can barely be seen. 155 00:10:50,292 --> 00:10:56,429 However, those particles are very good at absorbing the alpha particles emitted from the americium, 156 00:10:56,429 --> 00:11:01,741 and so not a lot of that kind of smoke is needed to set off one of these alarms. 157 00:11:02,000 --> 00:11:05,296 These very small, often invisible smoke particles 158 00:11:05,296 --> 00:11:08,731 are commonly emitted from things that are actively on fire. 159 00:11:08,731 --> 00:11:15,256 And this makes the ionization alarm technology particularly sensitive to the flaming stage of a fire. 160 00:11:15,256 --> 00:11:21,607 In fact, even apparently clean-burning flames can set them off - that may have been why just using the oven 161 00:11:21,607 --> 00:11:23,600 was prone to causing an alarm in my case. 162 00:11:24,320 --> 00:11:27,017 Car exhaust can also trigger these alarms, 163 00:11:27,017 --> 00:11:30,925 which is why smoke alarms are rarely recommended in garages. 164 00:11:30,925 --> 00:11:34,842 This has been a particularly puzzling  thing to me as, ya know, 165 00:11:34,842 --> 00:11:42,141 cars catch on fire sometimes and I would think a smoke alarm in the place where you keep your car is a decent idea. 166 00:11:42,141 --> 00:11:49,754 Anyway, while ionization alarms are really good — arguably too good — at detecting fine smoke particles, 167 00:11:49,754 --> 00:11:55,218 they are absolutely crap at detecting large smoke particles. 168 00:11:55,218 --> 00:12:01,963 If a room is slowly filling up with visible smoke, an ionization alarm may very well do nothing. 169 00:12:02,936 --> 00:12:07,741 You might think, "oh, so what? You said it’s good at detecting smoke from a flaming fire, 170 00:12:07,741 --> 00:12:11,440 and so long as it’s gonna wake me when a fire’s  actually happening what does it matter?" 171 00:12:12,400 --> 00:12:16,566 Well, most fires don’t just suddenly happen. 172 00:12:16,566 --> 00:12:18,018 They start slowly. 173 00:12:18,018 --> 00:12:21,351 And in the initial smoldering stages of a fire, 174 00:12:21,351 --> 00:12:25,222 the smoke particles tend to be the large, visible kind. 175 00:12:25,222 --> 00:12:31,716 If all you have in your home are ionization alarms, they may not react at all to that situation. 176 00:12:32,485 --> 00:12:33,841 And that’s bad! 177 00:12:34,080 --> 00:12:38,449 Studies comparing ionization and photoelectric  smoke sensing technologies 178 00:12:38,449 --> 00:12:42,229 have routinely shown that in the smoldering stage of a fire, 179 00:12:42,229 --> 00:12:48,022 photoelectric alarms respond much more quickly than their ionization counterparts. 180 00:12:48,022 --> 00:12:52,825 Some experiments have shown photoelectric alarms responding to the early stages of fire 181 00:12:52,825 --> 00:12:56,727 more than an hour before an ionization alarm does. 182 00:12:57,120 --> 00:13:00,486 Early warning of such fires is obviously valuable, 183 00:13:00,486 --> 00:13:07,558 and may give occupants time to find the source of the smoke and prevent  a destructive flaming fire altogether. 184 00:13:07,920 --> 00:13:11,920 And let’s not forget that smoke itself is very dangerous, 185 00:13:11,920 --> 00:13:15,760 with many fire-related fatalities happening due to smoke inhalation.   186 00:13:16,640 --> 00:13:21,036 In an Australian 60 minutes program which aired  back in 2014, 187 00:13:21,036 --> 00:13:25,919 a photoelectric alarm was activated about seven minutes into a simulated fire, 188 00:13:25,919 --> 00:13:33,343 meanwhile three ionization alarms didn’t respond at all to the very smoky test environment. 189 00:13:33,343 --> 00:13:35,108 Which is astounding! 190 00:13:35,108 --> 00:13:42,467 A smoke alarm which doesn’t react to a smoldering fire and a smoke-filled room isn’t a very useful smoke alarm. 191 00:13:43,120 --> 00:13:46,123 Some jurisdictions have reacted to this new knowledge 192 00:13:46,123 --> 00:13:52,837 by mandating photoelectric alarm technology and discouraging the use of ionization detectors. 193 00:13:52,837 --> 00:13:55,898 However, not all of them have. 194 00:13:55,898 --> 00:14:00,068 Ionization alarms still have that one narrow advantage; 195 00:14:00,068 --> 00:14:03,436 they do react more quickly to a flaming fire, 196 00:14:03,436 --> 00:14:07,849 and a photoelectric alarm needs  large-ish particles which can be seen, 197 00:14:07,849 --> 00:14:11,981 so fires which develop suddenly may not trigger them right away. 198 00:14:11,981 --> 00:14:14,157 Because of this situational difference, 199 00:14:14,160 --> 00:14:17,998 here in the US neither the The National Fire Prevention Association 200 00:14:17,998 --> 00:14:23,956 nor the United States Fire Administration take a firm position on the two technologies. 201 00:14:23,956 --> 00:14:29,034 They recognize the pros and cons but say that, since all fires are different, 202 00:14:29,034 --> 00:14:32,080 making a recommendation either way doesn’t make sense. 203 00:14:32,960 --> 00:14:35,112 And I sorta get that. 204 00:14:35,112 --> 00:14:38,160 If an ionization alarm is better in some fires, 205 00:14:38,800 --> 00:14:41,339 well then maybe it’s good to have them. 206 00:14:41,339 --> 00:14:46,955 But there are several problems with fixating on that situational speed benefit. 207 00:14:46,955 --> 00:14:54,715 The first is that fires which are suddenly flaming without having any smoldering action aren’t exactly common. 208 00:14:54,715 --> 00:15:01,200 It’s not like they never happen, one possible case might be if a cat knocks over a lit candle onto a tablecloth,   209 00:15:01,200 --> 00:15:06,321 but especially when people are sleeping, I don't think it's that common for a flaming fire 210 00:15:06,321 --> 00:15:07,928 to come out of nowhere. 211 00:15:07,928 --> 00:15:11,277 I spent some time looking for statistics and came up empty. 212 00:15:11,277 --> 00:15:14,720 If you know of a good source of  information regarding this please share it below. 213 00:15:15,440 --> 00:15:18,345 The second and perhaps most important issue here 214 00:15:18,345 --> 00:15:25,601 is that while ionization alarms are generally faster at detecting a flaming fire than their photoelectric counterparts… 215 00:15:26,472 --> 00:15:29,682 it’s a matter of seconds, and not minutes. 216 00:15:29,682 --> 00:15:35,360 When a house fire’s going on  it's not gonna be a nice clean burning fire for long at all, 217 00:15:35,360 --> 00:15:40,974 and smoke thick enough to trigger a  photoelectric alarm will accumulate pretty quickly. 218 00:15:40,974 --> 00:15:45,770 Surely there have been cases  in which the seconds mattered for survivability, 219 00:15:45,770 --> 00:15:53,840 but of course the counterargument is that a photoelectric alarm may have given you an hour’s advanced warning in a different situation. 220 00:15:53,840 --> 00:15:57,331 Now I can hear you asking; why not both? 221 00:15:57,331 --> 00:16:02,614 Smoke alarms are pretty cheap, so why not have both detection technologies? 222 00:16:02,614 --> 00:16:06,266 Well,  the smoke alarm manufacturers are way ahead of you 223 00:16:06,266 --> 00:16:09,441 offering dual-sensing alarms. 224 00:16:09,441 --> 00:16:11,712 There’s a problem with these, though. 225 00:16:12,000 --> 00:16:17,212 They aren’t exactly clear on how those sensors get used. 226 00:16:17,212 --> 00:16:23,432 The packaging of this one implies that it would sound the alarm if either sensor detects smoke, 227 00:16:23,432 --> 00:16:25,200 but the included user guide 228 00:16:25,760 --> 00:16:28,696 doesn’t clarify whether this is in fact the case. 229 00:16:28,696 --> 00:16:33,332 It simply says the alarm sounds when combustion products are detected. 230 00:16:33,332 --> 00:16:40,951 Some alarms like this may not go off unless both sensors agree that there is smoke - and in that case, 231 00:16:40,951 --> 00:16:47,624 you’re not actually getting any benefit at all as it will always be the slowest response between the two technologies. 232 00:16:47,624 --> 00:16:54,788 And the reason why they might be programmed this way has to do with the final major issue with ionization alarms; 233 00:16:54,788 --> 00:16:56,320 false alarms. 234 00:16:56,320 --> 00:17:01,853 A smoke alarm which goes off when it shouldn’t  is a nuisance that most of us have dealt with at some point. 235 00:17:01,853 --> 00:17:08,061 And ionization alarms, thanks to their hyper-sensitivity towards certain kinds of invisible smoke particles, 236 00:17:08,061 --> 00:17:12,400 are particularly prone to false triggers - especially when placed near kitchens. 237 00:17:13,280 --> 00:17:17,982 False alarms aren’t just annoying, though,  they are actually dangerous. 238 00:17:17,982 --> 00:17:24,598 That's because one of the most common ways people address a smoke detector which keeps detecting erroneous smoke 239 00:17:24,598 --> 00:17:27,833 is to take it down or otherwise disable it. 240 00:17:27,833 --> 00:17:32,800 And a disabled smoke alarm is exactly as effective as an imaginary one. 241 00:17:33,600 --> 00:17:38,210 Photoelectric smoke sensing is much less prone to false alarms. 242 00:17:38,210 --> 00:17:44,768 They’re not impervious to the problem - as a matter of fact I had one myself which developed a newfound sensitivity 243 00:17:44,768 --> 00:17:49,998 a few years after I first put it up and started going off  whenever I used the dryer. 244 00:17:49,998 --> 00:17:57,285 However in that case it was an electric dryer which vented directly into the hallway right where the alarm was 245 00:17:57,285 --> 00:18:03,087 so it wasn’t an ideal situation from the start. I think moisture probably killed it somehow. 246 00:18:03,087 --> 00:18:09,040 Anyway, as a more relevant example, since replacing this  alarm near the kitchen with a photoelectric unit, 247 00:18:09,040 --> 00:18:11,862 I haven’t had a single nuisance alarm. 248 00:18:11,862 --> 00:18:14,378 And that was well over a year ago at this point. 249 00:18:14,720 --> 00:18:16,785 So where does this leave us? 250 00:18:16,785 --> 00:18:18,400 The answer seems kinda murky. 251 00:18:19,040 --> 00:18:26,080 Ionization smoke alarms work very well in specific  circumstances, but hardly work at all in others.   252 00:18:26,080 --> 00:18:31,040 They’re also more prone to false alarms which  may make occupants more likely to disable them.   253 00:18:32,000 --> 00:18:37,920 Photoelectric alarms outperform them in smoldering  fires and are less prone to false alarms,   254 00:18:37,920 --> 00:18:42,268 but they aren’t quite as good at alerting you to fires-in-progress. 255 00:18:43,421 --> 00:18:45,159 So what should you do? 256 00:18:45,159 --> 00:18:48,582 Personally, I don’t think ionization smoke alarms 257 00:18:48,582 --> 00:18:54,832 present enough of a performance difference in active fires  to justify their continued use at all.   258 00:18:55,280 --> 00:19:03,131 Since 2008, the International Association of Fire Fighters has recommended against the use of ionization alarms, 259 00:19:03,131 --> 00:19:09,242 and as I’ve already said, some authorities have taken action and mandated the use of photoelectric alarms. 260 00:19:09,242 --> 00:19:15,612 In fact, an ever-increasing number of authorities across the globe, including some US states. 261 00:19:15,612 --> 00:19:22,193 But ionization alarms are still routinely sold in other places, including my home of Illinois. 262 00:19:22,193 --> 00:19:27,311 And unless you know what the differences between the two technologies are, 263 00:19:27,311 --> 00:19:30,235 you probably haven’t paid any attention to this. 264 00:19:30,235 --> 00:19:33,925 Making matters worse is that many alarms  that are out there in the wild 265 00:19:33,925 --> 00:19:37,164 don’t make it clear what technology they use. 266 00:19:37,164 --> 00:19:43,154 If you take a look at the ones on your ceilings or walls, there may be no indication at all! 267 00:19:43,154 --> 00:19:49,974 These brand new alarms, which are photoelectric, don’t say that anywhere except the box! 268 00:19:49,974 --> 00:19:56,630 This brand-name ionization alarm does say it’s ionization on the back, so that’s good I guess. 269 00:19:56,630 --> 00:19:59,904 The combo alarm also says it’s both. 270 00:19:59,904 --> 00:20:03,920 To tell what you have, take it off  the wall and see if there’s a label somewhere. 271 00:20:04,480 --> 00:20:09,360 Hopefully there is but if there isn’t, well  if you can see the insides of the alarm the   272 00:20:09,360 --> 00:20:16,283 ionization chamber is a pretty recognizable thing; usually it's some sort of cylinder and will have a radiation label on it, 273 00:20:16,283 --> 00:20:19,737 but it’s not always possible to get at the insides. 274 00:20:19,737 --> 00:20:20,982 [voiceover] Two quick things; 275 00:20:20,982 --> 00:20:26,240 I was apparently wrong about  there being a radiation label on the sensor body itself, 276 00:20:26,240 --> 00:20:31,927 and, speaking of the sensor body, the ionization  chamber didn’t quite look like what I expected it to 277 00:20:31,927 --> 00:20:35,120 since apparently the outer shell  forms one of the electrodes these days. 278 00:20:35,680 --> 00:20:41,221 Such are the perils of writing a script and  shooting the talky bits before actually taking the things apart. 279 00:20:41,221 --> 00:20:44,765 However, at least here in the US, if it’s an ionization alarm 280 00:20:44,765 --> 00:20:49,612 there’s probably gonna text regarding the fact that there’s americium-241 in there, 281 00:20:49,612 --> 00:20:52,537 with permission from the Nuclear Regulatory Commission. 282 00:20:52,537 --> 00:20:57,961 I don’t know what labels you might find in other countries, but if you see a warning about radioactive material, 283 00:20:57,961 --> 00:20:59,280 that’s an ionization alarm. 284 00:20:59,920 --> 00:21:07,227 Now, there is still the fact that ionization alarms may still be faster at alerting you to a sudden, flaming fire. 285 00:21:07,918 --> 00:21:15,337 It just doesn’t look to me and many other like this potential benefit outweighs the various downsides of the technology. 286 00:21:15,337 --> 00:21:20,408 However if you think it’s valuable to have an ionization alarm just in case, 287 00:21:20,408 --> 00:21:27,040 my recommendation would be to purchase a separate alarm and make sure to place it far away from your kitchen to prevent nuisance alarms.   288 00:21:27,760 --> 00:21:35,278 I personally wouldn’t trust one of these combo alarms because  it's just too unclear how the sensors actually get used in the logic - 289 00:21:35,278 --> 00:21:40,081 and two separate alarms are usually cheaper than one of these, anyway. 290 00:21:40,081 --> 00:21:47,520 For what it’s worth, I didn’t replace one of the ionization alarms here because it’s far enough from the kitchen to not be affected by cooking   291 00:21:47,520 --> 00:21:52,268 and having photoelectric alarms elsewhere makes me feel plenty safe. 292 00:21:52,268 --> 00:21:58,356 But when it’s no longer functional, I will probably go with a  photoelectric alarm to replace it. 293 00:21:58,356 --> 00:22:04,240 I don’t know if I would go so far as to call the ionization  chamber an obsolete form of smoke detection,   294 00:22:04,240 --> 00:22:06,553 but it’s definitely flawed. 295 00:22:06,553 --> 00:22:09,600 The more people that are aware of its weaknesses, the better. 296 00:22:10,496 --> 00:22:16,124 Before I go, you’ve probably seen recommendations  to replace smoke alarms every 10 years. 297 00:22:16,124 --> 00:22:23,533 In fact, these days smoke alarms with single-use  lithium cells which are designed to last 10 years are pretty common - 298 00:22:23,533 --> 00:22:27,963 and in some places, those are the only battery-operated kind available. 299 00:22:27,963 --> 00:22:32,342 Now, the recommendation has nothing to do with the americium. 300 00:22:32,342 --> 00:22:39,839 The half life of americium-241 is over 400 years,  so the sensor could easily outlive you. 301 00:22:39,839 --> 00:22:44,560 Instead the recommendation is to guard against  aging electronics causing unit failure. 302 00:22:45,520 --> 00:22:52,181 I’m sorta on the fence about this, because 10  years is a pretty dismal life expectancy. 303 00:22:52,181 --> 00:22:58,221 But on the other hand, these are cheap  and cheaply made so maybe it’s fair. 304 00:22:58,560 --> 00:23:06,195 What I wish were far more common was  actually testing your smoke alarms with a canned smoke product. 305 00:23:06,195 --> 00:23:11,094 Commercial fire alarm systems get  their smoke sensors actually tested this way. 306 00:23:11,401 --> 00:23:16,492 You might have seen someone going around with a little  spray can of magic smoke and puffing it into the sensors 307 00:23:16,492 --> 00:23:20,830 while radioing someone else at the  control panel who's looking for a response. 308 00:23:21,840 --> 00:23:25,977 It seems to me like cans of that stuff ought  to be available for the home 309 00:23:25,977 --> 00:23:28,531 and that we should be recommending using it. 310 00:23:28,531 --> 00:23:31,622 I mean, I’m sure you can find the stuff online somewhere 311 00:23:31,622 --> 00:23:36,598 but it has always seemed odd to me that we don’t recommend that strategy for the home. 312 00:23:37,280 --> 00:23:41,462 Seems to me like actually proving operation  of the sensor bit 313 00:23:41,462 --> 00:23:45,040 is more valuable than hitting a button and making sure it starts beeping. 314 00:23:46,064 --> 00:23:48,978 But what do I know, I just make YouTube videos. 315 00:23:49,925 --> 00:23:52,464 ♫ alarmingly smooth jazz ♫ 316 00:23:54,615 --> 00:23:57,666 Let me tell you, eve - well, that’s uh… 317 00:23:57,666 --> 00:23:58,702 [clears throat] 318 00:23:59,112 --> 00:24:02,116 I wrote it as “let me tell you” but I wanted to say it as “let me tell ya” 319 00:24:02,116 --> 00:24:04,696 and it’s those little details that’ll trip ya up. 320 00:24:04,696 --> 00:24:09,722 Well, that smoke alarm [clunk] which is now… yeah. 321 00:24:09,722 --> 00:24:11,960 Consult your local file ath…. 322 00:24:14,080 --> 00:24:16,033 File authority! 323 00:24:16,033 --> 00:24:17,142 Consult your local 324 00:24:17,142 --> 00:24:21,867 fileafloridaeyhamorffhhaffifceuuuigigrechoirmeninyourarea 325 00:24:21,867 --> 00:24:27,474 That knocks loose some of their electrons, resulting in some gas charged mole … frark! 326 00:24:27,474 --> 00:24:30,627 When those smark… smark porticles? 327 00:24:31,440 --> 00:24:35,806 That may have been why just using the oven was  prone to causing this alarm. 328 00:24:35,806 --> 00:24:37,194 To alarm. 329 00:24:37,194 --> 00:24:38,430 Shoot. 330 00:24:40,735 --> 00:24:45,093 You didn't actually pause the video and check your alarms, did you? 331 00:24:45,093 --> 00:24:48,900 Well, here I am again tell you to do it. 332 00:24:48,900 --> 00:24:52,264 The video's over now, you don't have any more excuses. 333 00:24:52,264 --> 00:24:53,906 DO IT.