domestic wc usage patterns

8/13/2019 Domestic WC Usage Patterns

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PergamonBurlding and Emronment, Vol. 31, No 4, pp. 3X5-392, 1 996

Copyright (0 1996 Elsevier Science Ltd. All rights reservedPrmted in Great Britain

0360-1323196 $15.00+0.00

PII: SO360-1323(96)00008-X

Domestic WC Usage PatternsERAN FRIEDLER*DAVID BUTLER*?DAVID M. BROWN*

(Received 7 August 1995; accepted 17 October 1995)

Despite contributing 3&40 of the total wastewater flow to building drainage systems, little iscurrently known concerning the detailed usage patterns of the domestic WC. A diary survey of WCusage was carried out on 135 households in southern England over seven consecutive days. Usagewas categorised as urine only, faeces only, combined urine and faeces, and other. The urine modeof use followed the expected bimodal p t te rn of morning and evening peaks, whilst the the numberoffaecal relatedflushes peaked only in the morning with no corresponding evening rise. Weekendpatterns were shown to differ from week-day usage, particularly in terms of the timing andmagnitude of the morning peak. Females were found to use the WC 17 more often than males,whilst males use it 1 more in faecal related mode. Differences were also established between agegroups with elderly people apparently having the highest WC usage. The application of cleaningagents was also shown to follow a distinctive diurn l pattern Copyright 0 1996 Elsevier ScienceLtd.

INTRODUCTIONPROGRESS in the design and simulation of buildingdrainage systems requires a more detailed knowledge ofthe usage and characteristics of common domesticappliances. Butler [l, 21 has shown how usage variessignificantly throughout the day and between appliances,and has identified the WC in particular as the

largest single contributor to total wastewater flow (3&40%)producer of the highest daily peak flowproducer of the largest instantaneous flush flowsource of most solids.

Despite this importance little is known of the detail of itsusage, particularly in respect of different modes of useand differences in use attributed to different sections ofthe community.

To address the issue, and provide further basic data, adomestic toilet usage survey has been conducted. Theresults obtained provide a detailed insight into the diurnaland sub-weekly variation of WC usage patterns withemphasis on the type of use (urine, faeces or other) andthe type of user. The issue of solids input via the WC wasaddressed in the survey as well, but is discussed elsewhere[3]. Additional important aspects associated withappliance water quality have also been tackled [4].

*Department of Civil Engineering, Imperial College ofScience, Technology and Medicine, London SW7 2BU, U.K.tTo whom all correspondence should be addressed.

THE SURVEYMethodology

The survey was conducted for seven consecutive daysin July 1994. The aim was to examine the WC usagepatterns in domestic dwellings. The study was carried outin two parts as follows.

In part I, a total of 3750 members of staff at ImperialCollege in London and WRc in Swindon and Med-menham were contacted and invited to participate in thesurvey. All employees were deliberately approached totry and gain a cross-section of participants and thusobtain as representative a sample as possible. Those peo-ple who agreed to take part were sent details of stage II.

The second stage consisted of two parts: questionnairesand diary sheets. A questionnaire was given to eachhousehold in order to elicit the following details con-cerning:

dwelling occupants: number, age, gender, profession,diet;WCs in the household: number in each cistern type(conventional low-level, dual-flush low-level, con-ventional high-level and dual-flush high-level);toilet paper in use: brand, number of ply, dimensions.

Each participating household was sent diary sheets inaccordance with the number of WCs within the house-hold. The volunteers (and their family and guests) wereasked to record carefully each time the WC was used.The following data were therefore requested:0.

day and time of use and user identification;type of use: urine, faeces, combines urine and faeces,other;

385


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386 E. Frieder et al.Table 1. Characterlstlcs of sample households

Household size distributionNumber of Household Sample U.K.*occupants No. %

I 32 24 232 62 46 323 14 IO 174 19 14 18

5+ 8 6 I 0

* Reference [1 I].t Reference [5].

number of sheets of toilet paper used;other substances disposed of down the WC -cleaningagents, gross solids, etc. (a guidance list of possiblesubstances was supplied to the participants);any additional details concerning specific or generaluse of the WC.

The sumpleFrom the large number of invitations sent out approxi-

mately 250 or 6.7% volunteered to take part in the survey,whilst 135 households actually satisfactorily completedthe work. This is a low response rate, but still representsa sample size of 3 14 people.

The sample female/male distribution was 51.9 and48.1% respectively, which closely follows the U.K.national figures of 51.1 and 48.9% [5]. Household sizesranged from 1 to 5 occupants as shown in Table 1 (withan average occupancy of 2.33 occupants/house). Theoccupancy distribution approximates the U.K. nationalfigures relatively well, with the exception of the two occu-pants per household category where the survey deviatessomewhat from the national trend.

The average age of participants was 33 years, with theyoungest and the oldest participants being two and 81years old respectively. Relatively good agreement existsbetween the survey population and U.K. national data,especially in the O-14, 15-29 and 45-59 age groups (Table1). The 3044 age group was over-represented in thesurvey, while all age groups over 60 years were under-represented. This bias was expected since the populationapproached had a relatively high proportion of people inthe working age group.

The proportion of vegetarians in the sample was 9.6%,which compares relatively well with the British nationalfigure of&g% [6]. During the sample period many house-holds received guests and these were found to be respon-sible for almost 3% of the total number of flushesrecorded.

The average number of WCs per household was foundto be 1.44 (coefficient of variation 0.47) with actualownership ranging from 1 to 4. Approximately 65% ofthe households had 1 WC, 26% had 2, and 8% had3. The total number of WCs surveyed was 195, whichcomprised four different cistern types: conventional low-level (SO%), dual-flush low-level (IO%), conventionalhigh-level (9%) and dual-flush high-level (1%).

Household age distributionAgerange

SampleNo. Sample%

U.K.-l-

&I415-2930-4445-5960-7475+Not indicated

59 18.X 19.464 20.4 21.5

107 34. I 21.263 20. I 17.310 3.2 13.7

I 0.3 6.9IO 3.2

Raw data were entered into a database, consisting ofabout 10,000 observations in all. All data were analysedusing the following procedure; observations were lumpedinto lo-minute time intervals, then normalised in accord-ance with sample size and duration of period covered (i.e.five days for week-days, two days for weekend days).Tables present normalised data, whilst figures presentdata which have been smoothed by means of a lo-minutemoving hourly average. Thus. the units used for pre-senting the results are either flushes/l00 capita/IO min(f/lOOc/lO min) or flushes/capita/day (f/c/d).

Data on WC usage have been placed into four cat-egories as follows:faeces only (F)0 urine only (U)

combined faeces and urine (FU)other (0).

Usage categorised as other (0) signifies a flush in whichnone of the other three modes was recorded. This modeoccurs when a second flush is required to clear the WCpan, following the use of cleaning agent, or for flushingsolid refuse.

Figure 1A and B show the patterns of WC uses over a24-hour period during an average week-day and an aver-age weekend day respectively. The U mode of use con-stituted the highest proportion of the total number offlushes during both week-days and weekend days. Thus.the diurnal pattern of total number of flushes follows thepattern of U mode closely. Average values for the wholepopulation were 2.96 for week-days and 3.44 U f/c/d forweekend days (Table 2), which are 74 and 72% of thetotal number of daily flushes respectively.

On week-days, U flushes show two distinctive peaks,each followed by a trough (Fig. 1A). A sharp peak occursduring the morning hours (5-9am), with a maximumvalue of 5.62 f/lOOc/lOmin. This peak is followed by aperiod of lower rate of flushes during mid-day. A secondprolonged peak occurs during the evening and this peaklasts for about four hours (7-l 1pm). The late night mini-mum also lasts for four hours, at a rate of approximately0.6Uf,/lOOc/10min. During this period the total numberof flushes results almost exclusively from the U mode ofuse.


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Domesti c WC Usage Patt erns 387

A Week Day9

0o:oo 03:oo 06:OO 09:oo 12:oo 15:oo 18:00 21:oo 24:00

n ther lushI\

rine- Faeces- - - Fseces Urine

Time lhrl

9-8 ~-

B Weekend Day

------Otherflush-___Ge- Faeces- - - Faeces Urine

\

303:oo 06:OO 09:oo 12:oo 15:oo 18:00 21:oo 2400

Time [hrlFig. I. WC modes of use - diurnal patterns.

On weekend days U flushes are more evenly distributedthroughout the day. However, they show a rather erraticbehaviour at the sub-hourly scale (Fig. 1B). The morn-ing peak starts approximately an hour later (6am) andis less sharp than the week-day one, peaking at4.1 U f/l00 c/10 min. After the morning peak the U flushrate descends steadily until 1pm and stays relatively con-stant until 9910pm, with the mid-day minimum beinghardly noticeable. The evening peak occurs at 11 pm atan approximate rate of 4-4.5 U f/lOOc/lO min. The latenight trough lasts from 2 am to 556 am and is very similarin magnitude to the week-day trough.

The FU mode of use follows the U mode in order ofsignificance, with average values of 0.82 FUf/c/d onweek-days and 1.07 FU f/c/d on weekend days (Table 2).This amounts to 21 and 23% of the total number of dailyflushes on week-days and weekend days respectively.

Unlike U flushes and contrary to expectations, FUflushes show only one significant peak, which occurs dur-ing the morning hours. During this peak FU flushes makeup 38-39% of the instantaneous total number of flushes,both on week-days and weekend days. On week-days themorning peak occurs between 5 and 9am and is rathersharp, while on weekend days the peaks starts about anhour later (6 am) and is more diffused, ending just before12 pm. During the rest of the day the flush rate is relativelyconstant at about 0.5 FUf/100c/lOmin. Close exam-

ination of the FU curve reveals a very mild mid-daytrough and evening peak on week-days, while on weekenddays the flush rate descends very slowly until the latenight minimum. During early hours of the morning thereare virtually no FU flushes either on week-days or week-end days. On week-days this period lasts from 2 to 4 am.During weekends this period is slightly shorter, startingat 3 am and ending at 4:30 am.

Both F and 0 modes of use have a relatively lowimportance as a proportion of the total number of toiletflushes. F flushes consist of about 2% of the total numberof flushes both during week-days and weekend days, withapproximate values of 0.09 and 0.08 f/c/d respectively. 0flushes are responsible for about 3% of the total numberof flushes, with approximate values of 0.11 and 0.16 f/c/dfor week-days and weekend days respectively.

Clearly, the pattern of total number of flushes reflectsthe summation of the patterns of the four different modesof use. The total daily number of flushes during weekenddays is higher than the total number of flushes duringweek-days (4.75 and 3.98 f/c/d, respectively). Thesevalues agree well with the range of 3.65.4 reported byother researchers [2,7,8]. During the weekend the diurnalpattern is slightly more uniform than the week-daypattern, as reflected in lower coefficients of variation (0.59vs 0.83, Table 2). The same trend of lower coefficient ofvariation appears of course in all modes of use, with the


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388 E Fr iedler et al

Table 2. WC modes of useFaeces Faeces + urine

Week-day Weekend Week-day WeekendF M Total F M Total F M Total F M Total

Ave* 0.05 0.07 0.06 0.06 0.06 0.06 0.56 0.58 0.57 0.71 0.75 0.74STD* 0.10 0.15 0.10 0.16 0.16 0.12 0.74 0.85 0.76 0.74 0.88 0.74cv 2.04 2.28 1.76 2.83 2.75 2.14 1.32 I .45 1.33 1.05 1.18 1.00Min* 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Max* 0.49 1.32 0.70 0.92 0.99 0.64 3.44 5.17 4.27 3.68 4.30 3.34Dailyt 0.07 0.10 0.09 0.08 0.08 0.08 0.81 0.84 0.82 I .02 I .08 I .07

Ave*STD*cvMin*Max*Dailyt

Ave*STD*cvMin*Max*Daily?

Other UrineWeek-day Weekend Week-day Weekend

F M Total F M Total F M Total F M Total0.09 0.06 0.08 0.12 0.09 0.11 2.23 1.78 2.05 2.50 2.12 2.390.17 0.13 0.14 0.22 0.19 0.16 I .lS I .48 1.59 1.57 1.39 1.39I .82 2.20 1.76 1.88 2.15 I .48 0.79 0.83 0.77 0.63 0.66 0.580.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.13 0.00 0.00 0.000.98 0.66 0.76 1.53 0.99 0.80 9.82 5.96 7.96 7.67 6.62 6.210.13 0.09 0.11 0.17 0.13 0.16 3.21 2.57 2.96 3.60 3.05 3.44

Faecal related flushes TotalWeek-day Weekend day Week-day Weekend day

F M Total F M Total F M Total F M Total0.61 0.65 0.63 0.76 0.81 0.80 2.94 2.49 2.76 3.38 3.01 3.300.81 0.95 0.84 0.82 0.97 0.82 2.42 2.22 2.29 2.08 I .94 I .941.32 1.46 1.34 1.07 I .20 1.02 0.83 0.89 0.83 0.62 0.64 0.590.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.19 0.00 0.00 0.163.80 6.49 4.97 4.29 5.30 3.82 12.52 11.13 II.15 10.12 8.61 8.600.88 0.94 0.91 1.10 1.16 1.15 4.23 3.59 3.98 4.87 4.34 4.75

*f/lOOc/lOmin.t f/c/d.F ~ female; M ~ male

exception of F mode where the weekend value is higherthan the week-day one.

Comparing the total number of flushes for differentweek-days reveals that they all show very similar diurnalpatterns (Fig. 2), as found in earlier work [2]. Saturday

reliably by two distinct profiles: an average week-day andan average weekend day.

FAECAL RELATED FLUSHES (FRF)and Sunday profiles were also found to be similar to thestandard weekend day. Thus, the week can be represented

In order to quantify all flushes related to faecal use, anew mode of use called faecal related flushes (FRF) has

3:oo 6:00 9:oo 12:oo 15:oo 18:OO 21:oo 24:00Time [hr]

Fig. 2. Week-days ~ diurnal patterns of total flushes.


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Domestic WC Usage Patt erns 389

40o:oo 03:oo 6:OO 9:oo 12:oo 15:oo 18:OO 21:oo 24:

Time [hr]Fig. 3. FRF flushes as a proportion of total flushes.

been calculated combining F and FU modes together.Daily averages of the FRF mode are 0.91 and 1.15 f/c/dfor week-days and weekend days respectively, which cor-respond well with literature data of 1 defecation/capita/day [7, 9, IO]. The high value obtained for week-days is quite surprising, especially in light of the factthat more than 70% of participants were working outof their household. This result might indicate thatpeople use the WC in FRF mode preferentially at homerather than at work.

Calculation of the proportion of FRF mode as part ofthe total WC flushes reveals that it consists of 0.23 and0.24 for week-days and weekend days respectively. TheFRF/total flush ratio varies significantly throughout theday (Fig. 3). The morning peak is bi-modal during theweek with maximum values appearing at 8 and lo:30 am(0.47, 0.42, moving average) and tri-modal on weekenddays, at 5:30, 9 and 11 am (0.38, 0.44 and 0.48 respec-tively, moving average). The peak period ends in a sharpdescent until 12pm (at 0.20, moving average). After12 pm the ratio continues to drop at a relatively constantslope while exhibiting an erratic behaviour. This con-tinues until night time where the FRF flushes consist of0.05-0.1 of the total flushes. During the week this lowratio remains until 3 am, when it ascends sharply towardsthe first morning maximum. On weekend days from 12to 1 am the ratio ascends to a maximum value of 0.25.This is followed by a rapid drop to zero between 3 and4 am, after which a sharp ascent occurs towards the firstmorning peak.

FLUSH VOLUMEThe WC was not always reported to be flushed after

each use. Although the participants were not askedexplicitly to indicate whether the WC was flushed aftereach individual use, some participants indicated whenhalf volume flush or no flush at all followed a particularuse. The participants who indicated variable flush volumesuggested water conservation as being the main reasonfor their practice. In all, 4.1% of the total recorded num-ber of uses was followed by half volume flushes, while2.5% was not followed by any flush at all. However itshould be noted that as expected the different modes of

use varied in this issue significantly. The F and FU modewere followed by a full volume flush almost exclusively,while 5.5 and 2.7% of the U mode uses and 16 and 0.7%of the 0 mode uses were followed respectively by halfvolume flush or no flush at all. From a practical point ofview, the proportion of uses which were followed by halfvolume flush or no flush at all is negligible. Thus, datafor flushes and uses can be used interchangeably.

SUB-GROUPS OF THE SURVEYEDPOPULATION

Femal e mal eFemales generally use the WC more than males, bothduring week-days (4.23 vs 3.59 f/c/d, Table 2) and duringweekend days (4.87 vs 4.34f/c/d). This results fromwomen having a higher number of U and 0 flushes thanmen. However, the number of F and FU flushes for malesis higher than the corresponding number of flushes forfemales. The diurnal patterns of all modes of use forfemales and males were found to be very similar.Age groups

The 304 volunteers (96.8% of the sample population)who indicated their age were divided into four age groupsin accordance with anticipated differences in their dailyroutines, as follows.

pre-school age ~ children from birth to four years old,with 11 individuals (3.5% of the sample);school age - children from five to 18 years old, with51 individuals (16.2% of the sample);working age - people from 19 to 64 years old, with238 individuals (75.8% of the sample);retired age - people of 65 years old and over, withonly four individuals (1.3% of the sample).

These sub-groups were found to differ significantly bothin daily number of uses of each mode and in the diurnalpatterns of use. As a generalisation our data suggest thatthe older a person is, the more times he or she uses theWC (Table 3). This is true for all modes of use with theexception of the F mode, where the number of recordswas too small to be able to draw conclusions. However,the proportion of each mode of use compared to the total


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390 E. Friedlev et alTable 3. Average number of WC uses vs age group

Age groupPre-schoolSchoolWorkingRetiredAverage

F* F+U* 0* U* Total*0.05 0.6 I 0.03 1.91 2.600.04 0.78 0.04 1.98 2.840.10 0.91 0. I5 3.27 4.430.00 I.50 0.14 4.82 6.460.09 0.89 0.13 3.03 4.13

* f,*c:d.

number of uses was found to be relatively similar for allage groups.

The retired age group was found to have the highestnumber of uses, with 6.46f/c/d (Table 3) followed bythe working age group with 4.43 f/c/d. The latter groupcovers a rather wide range of ages, but no significantdifferences were found between sub-groups. The schoolage group follows with 2.84 total f/c/d. The pre-schoolage group was found to have the least number of useswith 2.60 f/c/d. This age group includes babies who obvi-ously do not use the WC, a fact which may lower thenumber of uses even further. Indeed. one out of the I Irepresentatives of this age in the survey did not use theWC at all.

Figure 4 presents the diurnal patterns of total numberof WC uses for each age group during a typical week-day. The figure reveals that different daily habits of thesesub-groups are reflected in the diurnal patterns of theWC usage. The retired age group is not presented in thefigure due to paucity of data. However, the available datafor this group indicate that the WC usage is relativelyevenly distributed throughout the day (24 hours).

All age groups show a morning peak between 6 and9 am. The morning peak of the school and working agegroups is clearly defined, while it is much lower anddispersed for the pre-school group. Most of the activityof the pre-school age group takes place between 6 am and9pm, during which several peaks and troughs occur,namely morning, noon and evening peaks with troughsappearing after each one. After 9 pm the activity of thisgroup declines sharply and ceases totally at about mid-night after which no use was recorded until about5:30am. The school age group generally shows a less

evenly distributed activity than the pre-school age group.As stated before, the morning peak is significant with8.2 f/l00 c/10 min (moving average). This is followed bya sharp drop in the flush rate and a distinct mid-daytrough (0.5f 100c/lOmin) which lasts until 3pm. Theafternoon-evening peak starts at about 4pm and lastsuntil 9pm, with a rather constant flush rate of4 f/ 100 c/ 10 min. After 9 pm the flush rate declines steadilyuntil midnight, after which a very low rate of about0.1 f/ 100 c/l 0 min is maintained until 5 am.

The morning peak of the working age group reachesa maximum of 9.2f/l00c~l0min. This peak is followedby a prolonged trough until 3pm (with about1 i100c/lOmin). after which there is a steady increasetowards the evening peak. The evening peak occursbetween 7 and I1 pm; it starts with a steady rate of about4f/100c~lOmin (7_9pm), followed be a secondary peakreaching 6.2f/lOOc110min at I I pm.

After the evening peak the usage rate declines steadilyuntil 2am, after which it stays constant (at0.5f l00c~IOmin) until 5am when the morning peakbegins.

Obviously, the diurnal pattern of the average usagerate follows the pattern of the working age group closely.since this group was the most represented in the survey(75.8%). Similar general trends were found to exist dur-ing the weekend days, but the diurnal patterns for all agegroups were slightly more evenly distributed.

Vegetarian and non-vegetarian sub-groups were alsoexamined, but no real differences were found to exist.probabiy due to the relatively small number of veg-etarians (30 individuals), who were spread between vari-ous age groups. Differences were established between the

10

0o:oo 03:oo 06:OO 09: oo 12:oo 15:oo l O0 21:oo 24:00Time [hrl

Fig. 4. Age groups diurnal patterns of total flushes.


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Domestic WC U sage Patt er ns 3910.35

77%. 0.3e2 0.2508 0 2T2 0 15P04 0.1B 0 058

i nI -Week-dayI I - - - Weekend dayrI 1I 10:oo 3:oo 6:00 9:oo 12:oo 15:oo 18:00 21:oo 24:00

Time [hrlFig. 5. Cleaning agent applications ~ diurnal patterns.

sub-group affiliated to WRc (Swindon and Medmenham)and the one affiliated to Imperial College (London),mainly between the degree of variation in the diurnalusage patterns (i.e. timing and scale of peaks and troughsand general shape of the diurnal curve).

CLEANING AGENTSThe average application rate of cleaning agents was

recorded at 0.058 and 0.088 applications/c/d for week-days and weekend days respectively. Summation of thesevalues yields a figure of 0.47 applications/c/week.The product of this figure and the average householdoccupancy (2.33) yields a value of 1.1 appli-cations/household/week, which appears to be reasonablealthough it has not been substantiated from other sour-ces. Figure 5 presents the diurnal patterns of cleaningagent usage for week-day and weekend day. AlthoughFig. 5 presents data which was smoothed by means ofmoving hourly average, it shows quite an erratic behav-iour, resulting from the relatively few data reported. Bothcurves show one distinctive morning peak, after which arelatively low and constant rate is maintained throughoutthe day, with the exception of the early morning hourswere there is no use at all. During the week the morningpeak is very sharp, occurring between 7 and loam andpeaking at 0.32 applications/lOOc/lO min (moving aver-age). The weekend peak is more diffused in nature, star-ting at about the same time but ending as late as 3 pm,while the maximum rate of 0.27 applications/l00 c/10 minis reached at 12 pm.

CONCLUSIONSThe survey, carried out in southern England, revealed

distinctive diurnal patterns for each mode of use. Themost numerous mode of use was found to be urine (74and 72% of the total daily uses on week-days and week-end days respectively), followed by the faecal related flushmode (23 and 24% of the total daily uses on week-daysand weekend days respectively). The urine mode of useshowed distinctive morning and evening peaks, whilst therate of faecal related flushes showed only one distinctive

peak in the morning followed by a relatively low andconstant rate during the rest of the day.

Distinctive variation in all modes of use existedbetween week-days and weekend days. At weekends,people being at home use the WC more often thanduring the week, whilst the patterns of use differ too. Dur-ing the week the diurnal pattern is clearly defined, show-ing clear peaks and troughs, while during the weekendthe patterns exhibit a more erratic nature.

The survey established clear differences between maleand female use of the WC for all modes of use. Femalesuse the WC more often than males both on week-days(4.2 vs 3.6 f/c/d) and on weekend days (4.9 vs 4.3 f/c/d).Breaking down the total use into the various modes (F -faeces, 0 - other, U - urine, FU - faeces + urine, andFRF - faeces related flush) reveals that women use thetoilet for urine mode more than men (3.2 vs 2.6 for week-days, and 3.6 vs 3.0 for weekend days), while men use itmore in faecal related mode (0.94 vs 0.88 for week-days,and 1.16 vs 1.1 for weekend days).

Differences were also established between the four agegroups, namely (in descending order of uses per day):retired age (65 years and over), working age (19-64years), school age (5-18 years) and pre-school age (birthto four years). The daily number of WC uses per personfor each group was 6.46,4.43, 2.84 and 2.60 respectively.These age groups were also found to have different diur-nal patterns of WC usage. Whilst the oldest and theyoungest age groups showed a relatively evenly dis-tributed pattern, the working age and the school agegroups exhibited distinctive morning and evening peaks,each followed by a significant trough.

Cleaning agents input via the WC were found to have0.058 and 0.088 applications/c/d for week-days and week-end respectively. The application rate shows one peakduring the day. On week-days this peak is sharp in nature,while on weekend days it is more diffused and lasts for alonger period.Acknowlednementa-DMB wishes to acknowledee financial SUD-port from the Postgraduate Training Partnership Award fundedby EPSRC. WRc and the Deaartment of Trade and Industrv.E-F wishes to thank the Bnai-Brith Leo-Baek organisation fortheir financial support. The authors would like to thank all thosewho gave willingly of their time to participate in the survey.


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392 E Friedler et al.REFERENCES

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