A three year follow-up of asthma, respiratory symptoms and self-reported allergy, among pilots and cabin attendants

The influence of air humidification in aircraft, on perception of cabin air quality among airline crew (N = 71) was investigated. In-flight investigations were performed in the forward part and in the aft part on eight intercontinental flights with one Boeing 767 individually, equipped with an evaporation humidifier combined with a dehumidifying unit, to reduce accumulation of condensed water in the wall construction. Four flights had the air humidification active when going out, and turned off on the return flight. The four others had the inverse humidification sequence. The sequences were randomized, and double blind. Air humidification increased relative air humidity (RH) by 10% in forward part, and by 3% in aft part of the cabin and in the cockpit. When the humidification device was active, the cabin air was perceived as being less dry (P = 0.008), and fresher (P = 0.002). The mean concentration of viable bacteria (77-108 cfu/m(3)), viable molds (74-84 cfu/m(3)), and respirable particles (1-8 microg/m3) was low, both during humidified and non-humidified flights. On flights with air humidification, there were less particles in the forward part of the aircraft (P = 0.01). In conclusion, RH can be slightly increased by using ceramic evaporation humidifier, without any measurable increase of microorganisms in cabin air. The cabin air quality was perceived as being better with air humidification. PRACTICAL IMPLICATION: Relative air humidity is low (10-20%) during intercontinental flights, and can be increased by using ceramic evaporation humidifier, without any measurable increase of microorganism in cabin air. Air humidification could increase the sensation of better cabin air quality.

UNLABELLED:Health symptoms and perception of cabin air quality (CAQ) among commercial cabin crew were studied as a function of personal risk factors, occupation, and work on intercontinental flights with exposure to environmental tobacco smoke (ETS). A standardized questionnaire (MM 040 NA) was mailed in February to March 1997 to all Stockholm airline crew on duty in a Scandinavian airline (n=1857), and to office workers from the same airline (n=218). During this time, smoking was allowed only on intercontinental flights. The participation rate was 81% (n=1513) by the airline crew, and 77% (n=168) by the office group. Statistical analysis was performed by multiple logistic regression analysis, controlling for age, gender, atopy, current smoking habits, and occupation. The most common symptoms among airline crew were: fatigue (21%), nasal symptoms (15%), eye irritation (11%), dry or flushed facial skin (12%), and dry/itchy skin on hands (12%). The most common complaint about CAQ was dry air (53%). Airline crew had more nasal, throat, and hand skin symptoms, than office workers did. Airline crew with a history of atopy had more nasal, throat, and dermal face and hand symptoms than other crew members did. Older airline crew members had more complaints of difficulty concentrating, but fewer complaints of dermal symptoms on the face and hands than younger crew members did. Female crew members reported more headaches than male crew members reported. Smoking was not associated with frequency of symptoms. Pilots had fewer complaints of most symptoms than other crew had. Airline crew that had been on an intercontinental flight in the week before the survey had more complaints of fatigue, heavy-headedness, and difficulty concentrating. Complaints of stuffy air and dry air were more common among airline crew than among office workers from the same airline. Female crew had more complaints of stuffy and dry air than male crew had. Older cabin crew had fewer complaints of dry air than younger crew had, and cabin crew with atopy had more complaints of dry air than other crew had. Current smokers had fewer complaints of stuffy air than non-smokers had. Airline crew that had been on a flight on which smoking was allowed in the week before the survey, had more complaints of stuffy air, dry air and passive smoking, than crew that had not been on such a flight in the preceding week had.PRACTICAL IMPLICATIONS:Complaints on cabin air quality and health symptoms were common among commercial airline crew, and related to age, gender, atopy and type of work onboard. The hygienic measurements showed that the relative air humidity is very low on intercontinental flights, and particle levels are high on flights with passive smoking. This illustrates the need to improve the cabin air quality in commercial airlines. Such improvements could include better control of cabin temperature, air humidification, efficient air filtration with high efficiency particulate air filter (HEPA) filtration on all types of aircraft and sufficient air exchange rate in order to fulfil current ventilation standards.

The electronic and optical properties of the rutile titanium dioxide compound have been investigated experimentally by absorption measurements and theoretically by a full‐potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA). The thin films for the absorption measurements were prepared by DC magnetron sputtering. The theoretical results for the absorption compared qualitatively well with the experimental findings. The dielectric functions and band‐structure have also been calculated, and the LDA band‐gap energy is corrected by an on‐site Coulomb potential.

This paper describes the photoelectrochemical response in aqueous electrolyte of nitrogen-doped titanium dioxide, TiO2-xNx. Thin film electrodes were prepared by reactive DC magnetron sputtering in an environment of Ar, O-2, and N-2. A typical film thickness was 0.85 mum. The crystal structure of the photoelectrochemically active films was mainly of rutile character, and scanning and transmission electron microscopy showed a highly porous parallel penniform nanostructure. It was conclusively shown that dioxygen could be generated from water by illumination of the TiO2-xNx electrodes at moderate anodic potentials. The current density under 1000 W m(-2) visible light from a sulfur lamp was 0.2 mA cm(-2) at 0.55 V vs Ag/AgCl. Current-voltage characteristics under illumination were strongly dependent on the scan direction. Scanning the electrode from cathodic toward anodic potentials gave an onset potential similar to that of normal rutile TiO2, whereas a reversed scan gave an onset of photocurrent (depending on the light source) anodically upshifted by up to 0.8 V from its normal position. Moreover, a cathodic current was observed during the latter scans. This current was induced by the illumination at anodic potentials. This nonfaradic current was ascribed to photoinduced electron trap states distributed in an approximately 1.3 V wide range negative of the conduction band (CB) edge. These states also were active as electron-hole recombination centers. The density of this new set of states was similar to2 x 10(20) cm(-3), i.e., similar to the density of nitrogen atoms. They can be activated by light, even at wavelengths beyond 700 nm, and work as long-lived electron traps; hence, they have properties that are different from those of the earlier found Till (3d) states, also located below the CB of TiO2. The new states occur as a consequence of the nitrogen doping, but is not necessarily an intrinsic property of pure TiO2-xNx. Recombination via the new states-in conjunction with slow hole transport in the nitrogen-created band above the valence band edge-was suggested to be the cause of the large anodic shift of the onset potential for cathodic scans and of the moderate water oxidation efficiency of the TiO2-xNx thin film electrodes.

This paper describes the photoelectrochemical response in aqueous electrolyte for nitrogen-doped titanium dioxide, TiO2−xNx. The electrodes were prepared by reactive DC magnetron sputtering in an environment of argon, oxygen and nitrogen. The crystal structure of the photoelectrochemically active films was mainly of rutile character and scanning and transmission electron microscopy revealed a highly porous parallel penniform microstructure. The nitrogen-doped TiO2 generated a monochromatic incident photon-to-current efficiency response in good agreement with the optical spectrum. The onset wavelength for photoresponse was located around 550nm. The visible light response for TiO2−xNx compared to TiO2 prepared without nitrogen was considerably improved at moderate bias. However, severe recombinations were observed in the nitrogen-doped material indicating that the doping sites could serve as recombination centres.

The optical properties of the rutile titanium dioxide compound have been investigated experimentally by transmission spectroscopy measurements and theoretically by a full-potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA). The optical properties in terms of the dielectric functions and optical absorption coefficient have been calculated. The LDA band-gap energy is corrected by an on-site Coulomb potential. The resulting optical absorption were found to be in a very good qualitatively agreement with the experimental results. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Films of nitrogen-doped TiO2 were made by reactive DC magnetron sputtering in a mixture of argon, oxygen, and nitrogen. The nitrogen gas ratio Φ was varied in the 0 < Φ < 0.025 range during the depositions, resulting in TiO2-xNx films with 0 ≤ x ≤ 0.022 as determined by X-ray photoelectron spectroscopy. Structural and morphological properties of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning and transmission electron microscopy. Films prepared without nitrogen had a rutile structure, while the nitrogen-doped films were either rutile or anatase depending on Φ being below or above ∼0.007. Deposition rate, effective grain size, root-mean-square roughness, morphology, and optical absorption were also found to depend on Φ. The films were photoelectrochemically active, as reported in an earlier papers of ours [J. Phys. Chem. B 2003, 107, 5709−5716 and J. Phys. Chem. B 2004, 108, 5995−6003].

Nanocrystalline porous nitrogen doped titanium dioxide (TiO2) thin films were prepared by DC magnetron sputtering. Films were deposited in a plasma of argon, oxygen, and nitrogen, with varying nitrogen contents. The films were characterized by X-ray diffraction, scanning electron microscopy, and optical- and photoelectrochemical (PEC) measurements. These studies showed that the films were porous and displaying rough surfaces with sharp, protruding nodules having a crystal structure varying from rutile to anatase depending on the nitrogen content. All nitrogen doped films showed visible light absorption in the wavelength range from 400 to 535 nm. The PEC properties of the thin film electrodes were determined on as-deposited as well as dye-sensitized films. The nitrogen doped TiO2 generated an incident photon-to-current efficiency response in good agreement with the optical spectra. The PEC measurements on dye-sensitized films showed that the electron-transfer properties in the conduction band were similar to those of undoped TiO2. It was also experimentally confirmed that the states introduced by nitrogen lie close to the valence band edge. For the best nitrogen doped TiO2 electrodes, the photoinduced current due to visible light and at moderate bias was increased around 200 times compared to the behavior of pure TiO2 electrodes. There is an optimum in introduced nitrogen where the response is highest.

The aim was to determine cabin air quality and in-flight exposure for cabin attendants of specific pollutants during intercontinental flights. Measurements of air humidity, temperature, carbon dioxide (CO2), respirable particles, ozone (O3), nitrogen dioxide (NO2) and formaldehyde were performed during 26 intercontinental flights with Boeing 767-300 with and without tobacco smoking onboard. The mean temperature in cabin was 22.2 degrees C (range 17.4-26.8 degrees C), and mean relative air humidity was 6% (range 1-27%). The CO2 concentration during cruises was below the recommended limit of 1000 ppm during 96% of measured time. Mean indoor concentration of NO2 and O3, were 14.1 and 19.2 micrograms/m3, with maximum values of 37 and 66 micrograms/m3, respectively. The concentration of formaldehyde was below the detection limit (< 5 micrograms/m3), in most samples (77%), and the maximum value was 15 micrograms/m3. The mean concentration of respirable particles in the rear part of the aircraft (AFT galley area) was much higher (49 micrograms/m3) during smoking as compared with non-smoking conditions (3 micrograms/m3) (P < 0.001), with maximum values of 253 and 7 micrograms/m3. In conclusion, air humidity is very low on intercontinental flights, and the large variation of temperature shows a need for better temperature control. Tobacco smoking onboard leads to a significant pollution of respirable particles, particularly in the rear part of the cabin. The result supports the view that despite the high air exchange rate and efficient air filtration, smoking in commercial aircraft leads to a significant pollution and should be prohibited.

A unique nanostructured rod-like morphology of hematite (alpha-Fe2O3) designed with no grain boundaries, has been investigated for the aim of a direct splitting of water at the hematite/electrolyte interface. Photoelectrochemical properties were studied by steady-state measurements on electrodes with controlled morphology and Film thickness in aqueous electrolyte. The hematite electrodes were able to generate incident photon-to-current efficiencies (IPCEs) of similar to8% by illumination through the substrate with a wavelength of 350 run and a light intensity of 0.1 mW cm(-2) without any applied voltage. On the basis of light intensity studies, it is concluded that charge carrier recombinations due to the poor semiconductor properties in combination with slow oxidation kinetics at the hematite nanorods/electrolyte interface are the dominating problems. However, the high IPCE values obtained indicates that purpose-built nanorods of hematite is one significant way to strikingly lower the recombination rate of hematite material. (C) 2002 Elsevier Science B.V. All rights reserved.

Indium nitride (InN) and tin nitride (SnNx) films were produced with reactive d.c. magnetron sputtering technique. The thin film semiconductors were optically and photoelectrochemically characterised and the energetic positions of the two semiconductors’ band edges were determined with respect to the normal hydrogen electrode. The sputtered InN thin film showed an indirect bandgap of 1.4eV and a direct bandgap of 1.8eV. The optical spectra of SnNx indicated a bandgap energy of approximately 1.4eV. All nitride films showed n-type photoresponse in KI (aq) electrolyte at an irradiation intensity of 1000W/m2. The photoelectrochemical characterisation indicated that InN and SnNx with a bias of about 400mV or less can be used for photo-oxidation of water.

OBJECTIVE:To study symptoms among a commercial cabin crew, in relation to personal risk factors, perceived psychosocial work environment, occupation, and work on intercontinental flights, with exposure to environmental tobacco smoke (ETS).METHODS:A standardized questionnaire (MM 040 NA) was mailed in February-March 1997 to all Stockholm aircrew on duty in a Scandinavian flight company ( n=1,857), and office workers from the same company ( n=218). During this time, smoking was allowed only on intercontinental flights. The participation rate was 81% ( n=1,513) of the aircrew, and 77% ( n=168) of the office group. Statistical analysis was performed by multiple logistic regression analysis, keeping age, gender, atopy, current smoking, occupation, and perceived psychosocial work conditions simultaneously in the model.RESULTS:The most common symptoms among the aircrew were fatigue (21%), nasal symptoms (15%), ocular symptoms (11%), dry or flushed facial skin (12%), and dermal hand symptoms (12%). The aircrew had more nasal (odds ratio (OR) = 3.12), throat (OR=5.75), and dermal symptoms on the face (OR=2.03), and hands (OR=3.68), than the office workers. The aircrew with a history of atopy had an increase of most symptoms (OR=1.5-3.8), but age, gender, or smoking was not associated with symptoms. Perceived stress due to excess of work was associated with fatigue (OR=7.33), feeling heavy-headed (OR=9.52), headache (OR=5.10), and facial dermal symptoms (OR=3.75), while those crew with better work control and work satisfaction had less fatigue. For most symptoms, there were no differences between different categories onboard, but pilots had fewer ocular (OR=0.28) nasal (OR=0.52), and dermal hand symptoms (OR=0.39). Airline crew that had been on an intercontinental flight the previous week had more complaints of fatigue (OR=1.87), heavy-headedness (OR=1.89), and difficulties concentrating (OR=3.22).CONCLUSION:There was an association between symptoms and work stress, lack of influence on working conditions, atopy, and work on intercontinental flights where smoking was allowed. In view of the increase of civil aviation, the working conditions for aircrews need further attention.

OBJECTIVES Propylene glycol (PG) (1–2 propanediol; CAS No 57–55–6) is a low toxicity compound widely used as a food additive, in pharmaceutical preparations, in cosmetics, and in the workplace—for example, water based paints, de-icing fluids, and cooling liquids. Exposure to PG mist may occur from smoke generators in discotheques, theatres, and aviation emergency training. Propylene glycol may cause contact allergy, but there is sparse information on health effects from occupational exposure to PG. METHODS Non-asthmatic volunteers (n=27) were exposed in an aircraft simulator to PG mist over 1 minute, during realistic training conditions. Geometric mean concentration of PG was 309 mg/m3 (range 176–851 mg/m3), with the highest concentrations in the afternoon. The medical investigation was performed both before and after the exposure (within 15 minutes). It included an estimate of tear film stability break up time, nasal patency by acoustic rhinometry, dynamic spirometry, and a doctor's administered questionnaire on symptoms. RESULTS After exposure to PG mist for 1 minute tear film stability decreased, ocular and throat symptoms increased, forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) was slightly reduced, and self rated severity of dyspnoea was slightly increased. No effect was found for nasal patency, vital capacity (VC), FVC, nasal symptoms, dermal symptoms, smell of solvent, or any systemic symptoms. Those exposed to the higher concentrations in the afternoon had a more pronounced increase of throat symptoms, and a more pronounced decrease of tear film stability. In four subjects who reported development of irritative cough during exposure to PG, FEV1 was decreased by 5%, but FEV1 was unchanged among those who did not develop a cough. Those who developed a cough also had an increased perception of mild dyspnoea. CONCLUSION Short exposure to PG mist from artificial smoke generators may cause acute ocular and upper airway irritation in non-asthmatic subjects. A few may also react with cough and slight airway obstruction.

OBJECTIVES:This study determined the influence of exposure to environmental tobacco smoke (ETS) in aircraft on measured and perceived cabin air quality (CAQ), symptoms, tear-film stability, nasal patency, and biomarkers in nasal lavage fluid.METHODS:Commercial aircrews underwent a standardized examination, including acoustic rhinometry, nasal lavage, and measurement of tear-film break-up time. Eosinophilic cationic protein, myeloperoxidase, lysozyme, and albumin were analyzed in the nasal lavage fluid. Inflight investigations [participation rate 98% (N=39)] were performed on board 4 flights, 2 in each direction between Scandinavia and Japan. Scandinavian crew on 6 flights from Scandinavia to Japan participated in postflight measurements after landing [participation rate 85% (N=41)]. Half the flights permitted smoking on board, and the other half, 0.5 months later, did not. Hygienic measurements showed low relative air humidity on board (2-10%) and a carbon dioxide concentration of <1000 ppm during 99.6% of the cruising time.RESULTS:The smoking ban caused a drastic reduction of respirable particles, from a mean of 66 (SD 56) microg/m3 to 3 (SD 0.8) microg/m3. The perceived CAQ was improved, and there were fewer symptoms, particularly ocular symptoms, headache and tiredness. Tear-film stability increased, and nasal patency was altered.CONCLUSIONS:Despite a high air exchange rate and spatial separation between smokers and nonsmokers, smoking in commercial aircraft may cause significant air pollution, as indicated by a large increase in respirable particles. This ETS exposure is associated with an increase in ocular and general symptoms, decreased tear-film stability, and alterations of nasal patency.

OBJECTIVE:Our objective was to study the perception of cabin air quality (CAQ) and cabin environment (CE) among commercial cabin crew, and to measure different aspects of CAQ on intercontinental flights.METHODS:A standardized questionnaire was mailed in February-March 1997 to all Stockholm-based aircrew on duty in a Scandinavian flight company (n = 1,857), and office workers from the same company (n = 218). The answers were compared with an external reference group for the questionnaire (MM 040 NA). During this time, smoking was allowed on intercontinental flights, but not on other shorter flights. Smoking was prohibited on all flights after 1 September 1997. The participation rate was 81% (n = 1,513) in the aircrew, and 77% (n = 168) in the office group. Air humidity, temperature, carbon dioxide (CO2) and respirable dust were measured during intercontinental flights, during both smoking and nonsmoking conditions. Statistical analysis was performed by multiple logistic regression analysis, keeping age, gender, smoking, current smoking, occupation, and perceived psychosocial work environment simultanously in the model.RESULTS:Air humidity was very low (mean 5%) during intercontinental flights. In most cases (97%) the CO2 concentration was below 1,000 ppm. The average concentration of respirable particles was 67 microg x m during smoking conditions, and 4 microg x m(-3) during non-smoking conditions. Complaints of draftiness, too high temperature, varying temperature, stuffy air, dry air, static electricity, noise, inadequate illumination, and dust were more common among aircrew as compared with office workers from the same company. Female crew had more complaints on too low temperature, dry air, and dust. Current smokers had less complaints on stuffy air and environmental tobacco smoke (ETS). Younger subjects and those with atopy (childhood eczema, allergy to tree or grass pollen, or furry animals) reported more complaints. Reports on work stress and lack of influence on working conditions were strongly related to perception of a poor cabin environment. Flight deck crew had more complaints about inadequate illumination and dust, but less complaints about other aspects of the cabin environment, as compared with flight attendants. Aircrew who had been on a flight the previous week, where smoking was allowed, had more complaints on dry air and ETS.CONCLUSION:Complaints about work environment seems to be more common among aircrew than office workers, particularly draft, stuffy air, dry air, static electricity, noise, inadequate illumination and dust. We could identify personal factors of importance, and certain conditions that could be improved, to achieve a better perception of the cabin environment. Important factors were work stress, lack of influence on the working conditions, and environmental tobacco smoke on some longer flights. The hygienic measurements in the cabin, performed only on intercontinental smoking flights, showed that air humidity is very low onboard, and tobacco-smoking onboard leads to significant pollution from respirable dust.

Nanostructured WO3 thin films were prepared, and photooxidation of water at such films was studied in a pH 4.68 solution. The cathodic current at potentials below -100 mV versus a saturated Ag/AgCl electrode was related to the reversible intercalation of H+ and/or Na+. The photocurrent onset was at similar to 100 mV, and the saturation photocurrent was at potentials >800 mV. In the range 300-1000 mV, photocurrent increased linearly with the increasing light intensity, indicating that charge carrier generation dominates the photoelectrochemical cell. Under illumination, linear log\i\ versus potential (Tafel) behavior was registered in the range 300-650 mV. Tafel slopes and exchange current densities are reported. The incident photon-to-current efficiency (IPCE) and the quantum yield (Phi) were high, regardless of the incidence of the light (front side, EE, or backside, SE, illumination). Both IPCEEE and IPCESE increased with film thickness. The low wavelength edge of the action spectra was red-shifted and moved toward the absorption band edge. Both Phi(EE) and Phi(SE) reached a plateau region at shorter wavelength. In the plateau, (Phi(SE) was close to I and independent of the film thickness, whereas Phi(EE) was similar to 20% lower and decreasing with increasing film thickness. Adopting a simple diffusion model for the electron transport, the diffusion length of electrons (L) was estimated to be 6.7 mu m for a 5.0-mu m thick film. Higher activation energies, E-A, were obtained at lower potentials (e.g., 0.60 eV at 200 mV and 0.32 eV at 300 mV). The E-A was <0.21 eV in the range 400-700 mV, and decreased further to 0.06 eV at 1000 mV. The variation of E-A with potential was explained by the existence of a distribution of electron-trapping states in an energy range around 0.6 V below the conduction band.

Objectives: To measure and compare the urinary cotinine concentration (U-cotinine) in non-smoking cabin attendants (C/A) working with the Scandinavian Airlines System, before and after work on intercontinental flights with exposure to environmental tobacco smoke (ETS). Methods: The study material consisted of 24 cabin attendants and one pilot, all volunteers and all without exposure to ETS in the home, working on 15 intercontinental flights. Information on age, gender and occupation was gathered, as well as possible sources of ETS exposure in other places, outside work and during previous flights, during a 3-day period prior to the investigation. Urine samples were taken before departure and after landing, on board, and were kept frozen (−20 °C) until analysis. Cotinine was analyzed by a previously developed gas chromatographic method, using mass spectrometry (MS) with selected-ion monitoring (SIM). The difference in U-cotinine before and after the flight was compared. Moreover, the change in U-cotinine during the flight was related to occupation (work in the forward or aft galley) and observed degree of smoking during each flight. Results: The median U-cotinine was 3.71 μg/g crea; 2.4 μg/l (unadjusted) (interquartile range 2.08–8.67 μg/g crea) before departure, and 6.37 μg/g crea; 7.1 μg/l (interquartile range 3.98–19 μg/g crea) after landing, a significant difference (P < 0.003). C/A in the aft galley had a significantly higher concentration of U-cotinine after landing than subjects working in the front of the aircraft (P=0.01). In C/A working in the aft galley, the median increase of U-cotinine was 3.67 μg/g crea; 3.2 μg/l (interquartile range 0.04–13.8 μg/g crea) during flight. In contrast, those seven subjects working in the forward part of the aircraft had no increase in U-cotinine during the flight (median increase 0.97 μg/g crea; 0.5 μg/l interquartile range 0.27–2.65 μg/g crea). Conclusion: Tobacco smoking in commercial aircraft may cause significant exposure to environmental tobacco smoke among C/A working in the aft galley, despite high air exchange rates and spatial separation between smokers and non-smokers. This agrees with earlier studies, as well as measurements on the aircraft, showing a higher degree of ETS-related air pollution in the aft galley than in the forward galley. The average cotinine concentration in urine was similar to that in other groups with occupational exposure to ETS, e.g., restaurant staff, police interrogators and office workers. Since smoking in commercial aircraft may result in an involuntary exposure to ETS among non-smokers, it should be avoided.

Uninitialized variables are important to high-performance Prolog implementations since they can be bound much more efficiently than standard variables and may reduce the size of environments. In this paper, we propose a straightforward program transformation that detects uninitialized arguments to calls and rewrites the program to make such arguments obvious to the compiler. Our algorithm detects more uninitialized arguments than previously proposed methods, is robust when declarations are lacking and calling modes vary, and never performs worse than the monovariant method previously described in the literature. On a substantial set of benchmarks, our algorithm always performs as well as previous methods, and sometimes considerably better. The transformation adds specialized predicates to the program, on the order of 20% of the original number of predicates.