audible alarm waking effectiveness: low frequency alarm

Audible Alarm Waking Effectiveness: Low Frequency Alarm Sound Pressure Levels

JOSHUA DINABURG| SEPTEMBER 2019

2 | Copyright © 2019 Jensen Hughes. All rights reserved.

Research Foundation Literature Review and Gap Analysis

+ Low frequency alarms required for− Sleeping areas (fire alarm control panels)− Voice Notification Systems in Sleeping Areas− Mild to Severe hearing loss

+ Improved performance of Low frequency over high frequency alarms proven− Required SPL for devices remained unchanged− SPL at low frequency requires additional power− Research to justify a reduction in SPL for low frequency alarms

+ Sound Pressure Level SPL requirements for low frequency alarms have been questioned

Project Overview


Sound is an atmospheric pressure variation traveling as a wave

+ Humans can “hear” 20 – 20,000 Hz Tones− Hearing is a complex process− A-weighting scale to transform raw sound into human interpretation

+ Transport is complex− Reflection− Absorption− Interference− Modulation− Walls, floors, doors, corridors, carpets, composite barriers

Sound Pressure Levels


Relative Scale of Decibels

Sound Pressure

SPL(dB) = 10log10(sound pressure)²

(reference pressure)²= 20log10

sound pressurereference pressure

+ Based on minimum hearing threshold of humans – 0.00002 Pascals

+ Sound power is the square of the sound pressure

+ dB is related to sound power

+ A-weighting scale, correlated to human ear− Used for alarm signaling − Biased toward mid frequencies− May not be entirely accurate for perceived

“loudness” or for waking ability− Not based on loud tones (>60 dB)


Evolution of Codes and Standards Based on Research

+ Device Requirements− 85 dBA measured at a distance of 10 ft (UL 217 and UL 268)− Individual alarm system sounders can be 75 dBA at 10 ft (UL 464)

+ Installation Requirements− In residential occupancies, including one- and two-family dwellings− 75 dBA minimum at the pillow location (IBC, NFPA, International Requirements)− 15 dBA above ambient or 5 dBA above maximum ambient sound > 60 seconds (IBC, NFPA)

+ Sound Requirements− T-3 temporal pattern to ISO 8201 and ANSI S3.41− Low frequency 520 Hz square wave pattern in sleeping areas with fire alarm control panels, voice

notification systems in sleeping areas, and for hearing impaired for multiple and single station alarms

Current Requirements for Smoke Alarm SPL


1927 – Building Exits Code Call for a Distinctive Signal to be Standardized

EVOLUTION OF CODES AND STANDARDS

1927


1967 – NFPA 74 Standard for the Installation, Maintenance and Use of a Household Fire Warning System

• Alarm shall be audible in all bedrooms with the doors closed

• All Alarm Devices shall be rated not less than 85 decibels at 10 feet


1927 1967


1971 – Keefe et. al.

+ Tested 35 adult males+ 1000 Hz tones (dB = dBA)+ 50% waking effectiveness at 75

dBA+ Referenced in Numerous Future

Studies as basis for 75 dBA requirements

Early Research on Waking Effectiveness


1975 NFPA Convention – Major Discussion

+ Device Requirements – Standardization of Signals+ Proposals for frequency shifting signal, “slow whoop” or temporal signal (T3)+ Temporal variation won almost unanimously

− Logistics of replacing all existing alarm devices− Concerns about fixed tone and masking in unique ambient environments− Temporal tone could become recognizable with public education− Temporal tone could be implemented using an interrupter on any existing circuit

Standardization of Smoke Alarm Signal


1975 – NFPA 72G Includes T-3 Pattern description in the Appendix

Much debate about standard signal pattern and tone


1927 1967 1975


1976 – UL 217 – 85 dBA at 10 ft requirement

1979 – UL 268 – 85 dBA at 10 ft requirement

Based on NFPA 74 Requirements


1927 1967 1976 19791975


Direct Influence to Early Requirements in Codes and Standards+ 1978 NBS (later NIST) literature review by Petzoldt and Van Cott

- Note issues compared between sleep studies- Comparison of multiple data sets to Steinicke data by Lukas- ~50% waking at 75 dBA- Very steep slope in waking effectiveness v. SPL

+ 1978 Article by Berry, concern about 75 dBA assumption, concern- Review of Keefe et.al. and stress the fact that only 50% of participants awoke at an average of 75 dB.- Berry did not think a 50% waking response was sufficient for emergency signaling.- Also notes that NFPA 74 “audibility design” was for 70 dBA in bedrooms



Direct Influence to Early Requirements in Codes and Standards+ 1979 Myles and Fidell for Bolt, Beranek and Newman

- SPL of smoke alarms likely insufficient- Ambient noise not accounted for- Lack of specified tone is incorrect

+ 1980 Nober et. al. tested alarm waking effectiveness- Characterized alarms at 2000 and 4000 Hz peaks, 85 dBA at 10 ft- Tested 70 college students at 55, 70 and 85 dBA- Assumed 15-16.4 dBA reduction in SPL with bedroom doors closed (85 → 70 dBA)- All awoke even at 55 dBA with AC unit- No differences between 70-85 dBA, used as a justification for future codes and standards




1927 1967

1976 1979

1975 1980

1980 – NFPA 74 Adds Exception for appliances in bedrooms to be 75 dBA at 10 ft

Appendix includes reference that 85 dBA outside bedroom produces 70 dBA in a bedroom, or 15 dBA above 55 dBA ambient noise



1927 1967

1976 1979

1975 1980

1980 British Standard BS 5839-1

First recommendation for 75 dBA at the “bedhead”

1980



1927 1967

1976 1979

1975 1980

1985 – NFPA 72 G – 75 dBA at 10 ft for public mode

1985 – NFPA 74 F – 15 dBA over average ambient, 5 dBA over maximum

1980

1985


Determination of Resulting SPL from Source to Receiver+ Butler Bowyer and Kew 1981

- Method to calculate SPL based on distances and barriers and sound properties- Response to BSI 75 dBA at bedhead requirements- Included frequency components

+ Halliwell and Sultan 1985- Guide for engineering calculations- Method to calculate SPL at receiver

+ Schifiliti 1988- Fire Technology Article- Later become calculation for SFPE handbook, use BBK method, attenuation of SPL based on

frequency+ Details discussed further in justification

Engineering Calculations for SPL



1927 1967

1976 1979

1975 1980

1989 – NFPA 74 Requires interconnection of alarms in new construction

1980

1985 1989



1927 1967

1976 1979

1975 1980

1990 – NFPA 72 Incorporates NFPA 74F

DOES NOT INCLUDE 15 dBA or 5 dBA requirements

1980

1985 1990



1927 1967

1976 1979

1975 1980

1990 – BOCA NBC adopts 70 dBA minimum in Group R, 15 dBA above ambient and 5 dBA above maximum

70 dBA almost certainly based on assumption of 15 dBA attenuation of 85 dBA alarm through a closed bedroom door

1980

1985 1990

1990



1927 1967

1976 1979

1975 1980

1991 – SBCCI adopts same 70 dBA minimum (15, 5 dBA) requirements as BOCA NBC

1980

1985 1990

1990 1991



1927 1967

1976 1979

1975 1980

1993 –NFPA 72 Incorporates NFPA 74 and NFPA 72G

Includes 85 dBA requirement at 10 ft distance

Includes 75 dBA at 10 ft exception for devices in bedrooms

Interconnection of new construction

Alarms in every bedroom in new construction

Includes the 70 dBA requirement at the pillow (BOCA, SBC)

1980

1985 1990

1990 1991

1993



1927 1967

1976 1979

1975 1980

1995 – Canadian National Building Code

Requires T-3 Pattern (ISO 8201 ANSI S34.1)

75 dBA at the pillow required

1980

1985 1990

1990 1991

1993

1995


1995 - 1998

+ 1995 study (Bruck and Horason)- Hypothesis about naivety of signal increasing AAT- 60 dBA used based on measured alarm SPL in bedrooms- 21% did not wake at all

+ 1998 study - Alarms placed in hallways in real homes, families and various age subjects- Alarms placed in hallways outside all bedrooms, 60 dBA on average with closed doors at pillow- Children not awakened reliably 85% of the time- Confirmation of previous research by 1985 work by Busby and Pivik, children do not awaken, even

over 100 dBA

Waking Effectiveness Studies by D. Bruck at Victoria University


Grace – Duncan – Fleischman 1997-1999

+ Comprehensive literature review by Grace 1997+ Waking experiments by Duncan 1999+ Alarms placed in hallways, 3000 Hz tone from COTS ionization alarms+ Almost all participants awoke + Average alarm SPL of 72 dBA+ Non-waking participants

- Children- People who consumed alcohol

University of Canterbury



1927 1967

1976 1979

1975 1980

1999 – NFPA 72 removes the exception for 75 dBA at 10 ft for alarms in bedrooms, aligns with requirements for devices from UL 217/268

1980

1985 1990

1990 1991

1993

1995

1999



1927 1967

1976 1979

1975 1980

2000 – ICC consolidates NBC, SBC, UBC

Includes 70 dBA minimum at pillow, 15 and 5 dBA above ambient

1980

1985 1990

1990 1991

1993

1995

1999

2000


Ball and Bruck 2004

+ Comparison of waking effectiveness of young adults sober and under the influence of alcohol

+ Sober, BAC = 0.05, BAC = 0.08+ 12 dBA increase in performance of low frequency

alarm when sober+ Slightly reduced difference but still apparent for alcohol

population

Comparison of Low and High Frequency Alarms – Waking Effectiveness



1927 1967

1976 1979

1975 1980

2002 – NFPA 72 changes the 70 dBA pillow requirement to 75 dBA

Intended to harmonize with NBC Canada

Determination that 75 dBA has been technically justified

1980

1985 1990

1990 1991

1993

1995

1999

2000

2002


Ashley, Roby et. al. CSE 2005-2007

+ Study to evaluate effective notification for hard of hearing

+ Developed a sensor to activate alternate notification devices

+ Tested a real low frequency sounder

+ Low frequency was more effective across all subjects

+ Greatest improvement for hard of hearing population

Comparison of Low and High Frequency Alarms – Waking Effectiveness


Bruck, Thomas, and Kritikos 2006

+ 45 older adults+ Test of low frequency square wave v. high frequency pure tone alarm+ Low frequency achieve 81% effectiveness at 60 dBA, not 75 dBA

Direct Comparison of Low and High Frequency Waking Response

Low Frequency

500 Hz Male Voice High Frequency

AAT(dBA)

mean 48.0 52.6 55.9 63.7StDev 13.3 18.1 19.2 15.3

range 35-85 35-105 35-105 35-105median 45 45 50 65

N (%) slept 2 7 6 8thru 75 dBA (4.6%) (15.5%) (14.0%) (18.3%)

N (%) slept 1 3 4 2thru 85 dBA (2.3%) (6.6%) (9.3%) (4.6%)

N (%) slept 0 1 3 1thru 95 dBA (0%) (2.3%) (7.0%) (2.3%)

BehavioralResponse

Time

mean 93.3 124.5 153.9 192.1StDev 77.9 121.8 147.7 105.2

range 6-324 8-600 19-600 11-600

Median 75 83 91 197.5



1927 1967

1976 1979

1975 1980

2009 – ICC Codes change from 70 dBA at pillow to 75 dBA to align with NFPA 72

1980

1985 1990

1990 1991

1993

1995

1999

2000

2002

2009


Multiple Studies comparing low frequency to high frequency

Consistent over all tested populations >10 dBA reduction in SPL for low frequency to wake equivalent percentage of subjects

Waking Effectiveness Studies by D. Bruck at Victoria University

Test Group

Number of

Subjects

Waking Effectiveness of SPL ≤ 75 dBA –3100 Hz Tones

SPL of 520 Hz tone to achieve

equivalent effectiveness

Reduction in SPL for Equivalent

WakingOlder Adults 65-83 42 81% 61 dBA -14 dBA

Adults with hearing loss 38 56% <55 dBA > -20 dBASober young adults (18-

26) 14 57% 61 dBA -14 dBA

Young adults BAC = 0.05 14 36% 63 dBA -12 dBA

Young adults BAC = 0.05 32 61% 55-65 dBA -10 to -20 dBA

Young adults BAC = 0.08 14 36% 65 dBA - 10 dBA



1927 1967

1976 1979

1975 1980

2010 – NFPA 72 Includes Requirements for 520 Hz Square Wave

Sleeping Areas and for Hard of Hearing (effective Jan 2014)

1980

1985 1990

1990 1991

1993

1995

1999

2000

2002

2009

2010



1927 1967

1976 1979

1975 1980

Low Frequency Requirements Proliferate into UL Standards

ICC Codes Reference 2010 NFPA 72 (de Facto inclusion of low frequency requirement

1980

1985 1990

1990 1991

1993

1995

1999

2000

2002

2009

2010

2012


Evolution of Codes and Standards Based on Research

+ Each change in code or standard either proliferated from other code or justified by state of the art research

+ Research projects evaluated as basis for each code change+ Original device based requirement – 85 dBA at 10 ft from 1967 is still the standard

− Based on alarms located outside bedrooms− Estimates of sound attenuation through closed doors (~15 dBA)− Estimates and early test data (1970s-1980s) that 65-75 dBA is effective at waking normal hearing

college aged adult populations+ Installation based requirements

− 70 dBA (legacy), 75 dBA (current)− Based on comparable assumptions about SPL attenuation and effectiveness

Current Requirements for Smoke Alarm SPL


Considerations for Evaluation of DataWhat was the original basis for 85 dBA at 10 ft for all alarms?+ Is this basis still valid now that alarms are required in all bedrooms and with interconnection?+ Why was the 75 dBA at 10 ft exception for alarms in bedrooms removed in 1999?+ Given alarms outside of bedrooms, is the 85 dBA requirement even sufficient to alert most occupants?Why does the 520 Hz square wave tone awaken more effectively than traditional alarms greater than 2000 Hz?+ Is it because of the complex harmonic nature of the tone compared to pure tone alarms?+ Is it because of the increased total sound power due to A-weighting of SPL?+ Is it because the tone is unique and we are desensitized to the other beeps (electronics, dishwasher,

microwave, etc) compared to 30 years ago?Can a reduction in SPL be predicated on the assumption that they will be installed in bedrooms?+ Can we assume the public will install them correctly?+ Can we justify a reduced SPL based on alarms installed in hallways outside closed bedrooms?

Questions to be Answered


Why does low frequency work better?

+ Validity of A-weighting scale − 6 dBA difference in physical sound pressure from

3200 Hz or 520 HZ tone− Validity of B-weighting scale for >70dB signals− ISO 532 methods for calculating loudness for

complex tones+ Waking experiments of Levere 1972

− Demonstrated improved waking effectiveness to low frequency 125 and 250 Hz tones

− Believed waking in deep slow wave sleep a function of physical SPL, not dBA

Justification for Reduction in SPL


Equivalent Waking Performance at Reduced SPL – BAC = 0.05

+ Data of D. Bruck et al in development of 520 Hz requirements− Demonstrates equivalent waking performance

to high frequency at ~10-20 dBA reduction in SPL

− Measurements over a range of at-risk populations and experiments

+ Establish benchmark level of performance+ Find SPL that exceeds that benchmark



Equivalent Waking Performance at Reduced SPL – Older Adults

+ Data of D. Bruck et al in development of 520 Hz requirements− Demonstrates equivalent waking performance

to high frequency at ~10-20 dBA reduction in SPL

+ SIMILAR REDUCED SPL FOR HARD OF HEARING, CHILDREN, AND GENERAL POPULATION



Butler Bowyer and Kew 1981

+ Evaluation of sound transport through partitions+ As a function of frequency, low frequency transports more efficiently with less reduction of SPL+ -7 dBA for 500 Hz compared to 3000 Hz

Engineering Calculation – Sound Transport

Frequency of Sounder

C7

500 Hz 0

1000 Hz -3 dbA

2000 Hz -5 dBA

4000 Hz -9 dBA


Robinson 1986

+ Attenuation of SPL as a function of distance is reduced for 500 Hz compared to 1000 Hz+ Minimal difference in attenuation through partitions

Engineering Calculation – Sound Transport


White Noise Source – Broad Spectrum+ Halliwell and Sultan 1986+ Sound loss from corridor through door

into living room and bedroom

+ Penetration of low frequency sound below 300 Hz is greatest

+ 500 Hz is approximately 4 dB less attenuation than 2000-3000 Hz

+ Coincidence dip occurs at 2000-4000 Hz for apartment doors and walls, benefit transport of these tones

Measured SPL in Apartments from Corridor Alarms


Measured SPL in various conditions

+ Thomas and Bruck 2010

+ 85 dBA and 105 dBA source tones+ Measured in real homes with

sounder and receiver in various locations

+ Doors open and closed

+ Low Frequency consistently 5 – 9 dBA higher in receiver locations for all conditions

Measured Sound Pressure Levels – Low Frequency v. High Frequency Alarms

Doors

Signal type/level (Hz/dBA) n

Maximum reading (dBA)

Median reading (dBA)

Minimum reading (dBA)

Mean (dBA)

% ≥75 dBA

Hallway to Bedroom Analysis by Thomas and Bruck [119]

Closed

3100 85 42 55.9 44.8 37.4 45.5 0520 85 42 67.5 52.7 39.2 51.8 0

3100 105 42 76.8 62.3 49.3 62.9 ~5520 105 42 86.9 72.4 55.7 71.1 ~30

Open

3100 85 72 74.8 57.2 40.0 56.9 0520 85 72 76.8 64.2 46.4 63.2 ~5

3100 105 72 94.6 75.7 59.8 75.8 ~55520 105 72 104 84.0 64.4 83.7 ~80

Hallway to Bedroom Only – 2019 Analysis

All

3100All

88 91.6 61.3 37.6 60.0 ±13.1 14.8

520 88 95.1 68.7 41.6 67.5 ±13.1 33.0

Closed

3100All

44 75.7 51.5 37.6 54.2 ±11.0 4.5

520 44 86.9 62.5 41.6 62.5 ±12.0 22.7All Room of Origin and Measurement Locations – 2019 Analysis

All

3100All

1085 99.4 49.6 34.2 52.8 ±12.9 6.8

520 926 97.8 56.8 33.1 58.5 ±14.8 15.4

310085

543 81.9 42.6 34.2 45.5 ± 8.3 0.4

520 469 79.1 47.5 34.2 50.5 ±10.6 2.6


Frequency to reach given SPL

+ Comparable when bedrooms closed, doors open, only alarms in hallways, etc.

+ Utilizing 75 dBA at pillow threshold, LFA more than twice as likely to achieve threshold

+ Consistently more likely to be louder than a high frequency alarm

Measured Sound Pressure Levels – Low Frequency v. High Frequency Alarms


Effectiveness of Low Frequency Alarms

+ In all tested scenarios awoke more subjects at lower SPL+ 10-20 dBA to achieve equivalent performance+ Equivalent to high frequency alarms is waking of 50-90% of occupants, is equivalent really sufficient?

Conclusions


Sound Perception and Transport

+ Complex tone with multiple harmonics is less likely to be masked by ambient sounds+ Less likely to create null zones or destructive interference, dead zones in rooms+ Complex sound with increased apparent loudness, not quantified by dBA

+ Transport experiments show 5-9 dBA increase in SPL for low frequency tone v. 3100 Hz pure tone+ Increased transmission through barriers and partitions+ Increased linear transport / less absorption as a function of distance down corridors

Conclusions


Perception of Sound

+ A-weighting based on low limit of perception 40 phon+ A-weighting requires 6 dB increase in SPL to get equal dBA level – 4 times power increase+ A-weighting may not be applicable in deep sleep+ Validity of A-weighting for children, elderly, or hard of hearing?

Conclusions


Based on SPL at the ear and transport of sound lower frequency square wave is superior to high frequency alarm, but:

+ What level of waking effectiveness is sufficient, is equal to high frequency at 75 dBA enough?+ Why is the low frequency tone more effective?

- Complex tone, multiple frequencies and harmonics- Fullness of sound, perception of loudness- dBA weighting compared to other scales- Perception during sleep and scales and weighting

+ Could we justify a change for only bedroom installations?+ Is there sufficient data to justify a change assuming the public may only install in hallways, or on a

single floor?

Gaps


Too Many to Count – See Research Foundation Report

References

[101]

D. Bruck, I. Thomas and M. Ball, "Optimizing Fire Alarm Notification for High Risk Groups Research Project: Waking Effectiveness of Alarms (auditory, visual, and tactile) for the alcohol impaired," The Fire Protection Research Foundation, Quincy, MA, 2007.

[102]

D. Bruck and M. Ball, "Optimizing Emergency Awakening to Audible Smoke Alarms: An Update," Human Factors, vol. 49, no. 4, 2007.

[103]

R. Shifiliti, "Comment of Proposal No. 72-367. In," in Report of the Committee on Signalling Systems for the Protection of Life and Property, 2005.

[104]

D. Bruck and I. Thomas, "Towards a Better smoke Alarm Signal - an Evidence Based Approach," in Fire Safety Science Proceedings of the Ninth International Symposium, Karlsruhe, Germany, 2008.

[105]

D. Bruck and I. Thomas, "Comparison of the Effectiveness of Different Fire Notification Signals in Sleeping Older Adults," Fire Technology, vol. 44, pp. 15-38, 2008.

[106]

D. Bruck, M. Ball, I. Thomas and V. Rouillard, "How does the pitch and pattern of a signal affect auditory arousal thresholds?," Journal of Sleep Research, vol. 18, no. 2, pp. 196-203, 2009.

[107]

I. Thomas and D. Bruck, "Awakening of Sleeping People: A Decade of Research," Fire Technology, vol. 46, pp. 743-761, 2010.

[108]

M. Pilon, A. Desautels, J. Montplaisir and A. Zadra, "Auditory arousal responses and threshold during REM and NREM sleep of sleepwalkers and controls," Sleep Medicine, 2012.

[109]

D. Bruck and I. R. Thomas, "Community-based research on the effectiveness of the home smoke alarm in waking up children," Fire and Materials, vol. 36, pp. 339-348, 2012.

[110]

R. Roberts, "Technological Advances in Smoke Alarms," Honeywell Fire Safety, St. Charles, IL, 2013.

[111]

C. Lykiardopoulos, "Psychotropic Drug Usage and Human Behavior During Fire Emergencies," Victoria University, Melbourne, Australia, 2014.

[112]

Edwards Detection and Alarm, "Low Frequency Emergency Signaling Handbook: A Practical Guide to compliance and its history," United Technologies Corporation, Mebane, NC, 2015.

[113]

M. Myles and S. Fidell, "Evaluation of the Detectability of Residential Fire Alarms," in Report No 3833, Bolt Beranek and Newman, Inc., Prepared for Edwards Company, December 1978.

[114]

Owens-Corning Fiberglass Corp., "Solution to Noise Control Problems in the Construction of Houses," AIA File No. 39-E, 1966.

[115]

R. P. Schifiliti, "Designing Fire Alarm Audibility," in SFPE Handbook of Fire Protection Engineering, Gaithersburg, MD, Society of Fire Protection Engineers, 2016, pp. 1359-1369.

[116]

R. E. Halliwell and M. Sultan, "Attenuation of Smoke Detector Alarm Signals in Residential Buildings," in Fire Safety Science - Proceedings of the First International Symposium, Gaithersburg, MD, 1986.

[117]

H. J. Oyer and E. J. Hardick, "Response of Population to Optimum Warning Signal," Contract Report ODC-OS-62-182, 1963.

[118]

I. Thomas and D. Bruck, "Smoke Alarms in Dwellings: Timely Activation and Effective Notification," Center for Environmental Safety and Risk Engineering, Melbourne, Australia, 2010.

audible alarm waking effectiveness: low frequency alarm

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