intelligent monitoring of toxic gases for the construction workers in mining (1)

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN

0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME

282

INTELLIGENT MONITORING OF TOXIC GASES FOR THE

CONSTRUCTION WORKERS IN MINING

A.Sundaravadivelan (M.E), R.Vishnupriya M.E, R.Boopathi M.Tech, K.Sathish(M.E)

V.R.S.College of Engineering & Technology, Arasur

ABSTRACT

The wearable computing and treatment system are used to protect the construction

workers from toxic gases such as carbon-mono oxide (CO) and methane (CH4) poisoning. These poisoning are significant problem for construction workers employed in gold mining and gold cyanidation. A pulse oximetry sensor has been integrated into a typical prototype to allow continuous and non-invasive monitoring of workers blood gas saturation levels. These sensor systems monitor the condition of the workers automatically by sensing CO and CH4 level of the environment around the workplace and as well as individual heart beat of the worker. The sensor output is signal conditioned and it is digitized by using an analog to digital converter. The Microcontroller controls the operation of the ADC and the digital output of the ADC is transferred to the input port of the microcontroller. Then the transmitter section transmits that digital output to the receiver section. When the CO content of the environment goes above a threshold level the microcontroller automatically turns ON the Buzzer to indicate the critical condition. In the receiver section will be having GSM Modem to send the condition that presents in the workplace to the supervisor. Index Terms- Toxic gases, CO, CH4, Helmet prototype 1. INTRODUCTION

This technique presents and prevents the workers from toxic gas poisoning, when they

are employed in mining. This danger exists because the exhaust from mine- powered hand tools can quickly build up in enclosed spaces and easily overcome not only the tool’s user but co-workers as well. While the dangers of these toxicants are known, current safety systems for construction workers can only monitor the environmental concentrations. This is insufficient because toxic exposure affects people at different rates based on their activity level, body size and more significantly, their background risk factors such as smoking, anemia or prior exposure on the job site.

INTERNATIONAL JOURNAL OF ELECTRONICS AND

COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print)

ISSN 0976 – 6472(Online)

Volume 4, Issue 1, January- February (2013), pp. 282-293 © IAEME: www.iaeme.com/ijecet.asp

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Cyanide is a toxic substance which contains a group of chemicals containing carbon and nitrogen. These compounds are included by natural occurrence and human-made activities. This cyanide is used in mining to extract gold from ores, particularly low-grade ores and ores that cannot be readily treated through simple physical processes such as crushing and gravity separation.

Carbon mono-oxide is evolved during mining process, which is a colorless, odorless gas which competes directly with oxygen in binding with hemoglobin. It is also a toxic substance; it affects the human blood gas saturation level. To monitor the workers for the presence of carbon mono-oxide, Pulse oximeter is used to non-invasively measure hemoglobin concentrations within the body. Pulse oximetry is an approximation of Beer’s law which relates attenuation of light through a medium based upon the compounds it passes through.

Methane is an odorless, colorless gas or a liquid in its cryogenic form. Both the liquid and the gas pose a serious fire hazard when accidently released. The liquid will rapidly boil to the gas at standard temperatures and pressures. As a gas, it will act as a simple Asphyxiant and present a significant health hazard by displacing the oxygen in the atmosphere. The gas is lighter than air and may spread long distances. Distant ignition and flashback are possible. It is widely distributed in nature and the atmosphere naturally contains 0.00022 percent by volume (2.2 ppm)

Zigbee is a specification for a suite of high level communication protocols using small, low-power digital radios based on the IEEE 802.15.4 -2003 standard for wireless personal area networks(WPANs), such as wireless headphones connecting with cell phone via short –range radio. The MRF24J40MA is a 2.4 GHz IEEE Std compliant, surface mount module compatible with microchip’s Zigbee , MiWi and MiWi P2P software stacks.

The Microcontroller P89V51RD2 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. A key feature is it can operate in X-2 mode. The on-chip Flash allows the program memory to be re-programmed in-system or by a conventional non-volatile memory programmer. P89V51RD2 has the following features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, watchdog timer, two data pointers, three 16-bit timer/counters, a six vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry.

Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. It is a Pan-European mobile cellular radio system operating at 900 MHz. A switched-on mobile station with a SIM module attached. This can be used to send short message (SMS) to different user.

2. OVERVIEW

The implemented technique in the past includes only Infrared (IR) imaging. It is the

best method for detecting leaks of pollutant gases, but current technology based on cooled IR imagers which is expensive ($75,000 to $150,000) for field used to meet the need of regulatory limits—electric and petrochemical utilities, manufacturing plants and businesses such as supermarkets. Agiltron has demonstrated a new class of IR imager instrument for the detection of leaks of pollutant gases. Variants of the camera will be demonstrated for the long-wave (8-12 µm) and mid-wave (3-5 µm) IR, which will be able to locate leaks for dozens of pollutant gases. The proposed technology combines Agiltron Light



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Lever photomechanical thermal imager technology with a tunable IR filter developed originally for the telecommunications industry. Agiltron is implemented by the feasibility of the long-wave version using sulfur hexafluoride as a target gas. The mid-wave version will be able to visualize leaks for methane, benzene and volatile organic compounds (VOCs).

The proposed method to overcome the drawbacks of implemented techniques provides a feasibility study of a wearable computing system to protect construction workers from carbon mono-oxide poisoning. A pulse oximeter sensor has been integrated into a typical construction helmet to allow continuous and non-invasive monitoring of workers blood saturation levels. To show the feasibility of monitoring for carbon monoxide poisoning without subjecting the users to dangerous conditions as such a prototype for monitoring blood O2 constructed and tested during a user study involving typical construction tasks to determine its reliability while undergoing motion. Because monitoring for blood O2 and CH4 involve the same principles and technologies, if monitoring O2 is feasible, then monitoring for CH4 will be feasible as well. The results of integrating an oximeter into a construction-helmet will warn the user of impending carbon monoxide poisoning with a probability greater than 99%.

3. BACKGROUND WORK

Designing a wearable medical device for the construction workers involves a highly

interdisciplinary approach involving human physiology, uptake of simulation, wearable computing and reliability analysis. Providing the history and background for each subject is unnecessary as each subject is much larger than the other methods required in this project.

Fig.1. Transmitter section prototype

In fig.1, the transmitter section contains the Controller, Sensors, Zigbee module and power supply unit. These circuits are compatible and enclosed in a protective helmet. The helmet serves both physical protection and also protection from toxic gases. When a toxic gas is evolved, it is detected by the gas sensors. In mining, cyanide, carbon mono-oxide and methane gases are evolved. This toxicity is detected by the respective sensors. Each and every sensor has its threshold value. The values are measured in ppm.



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In fig.2, the receiver section contains the Zigbee module, relay circuit, PC system and GSM modem. It receives the information from transmitter section and drive the relay circuit to rescue the mining workers. PC system is used to note the blood gas level of the individual workers and if the threshold level may reach or goes above the threshold level. It sends the indication to the supervisor, wherever they localized. In order for an oximeter to function, light emitted from the LED must be able to pass through the vascular tissue and back to the PD. This can either be accomplished by transmitting light directly through the tissue to the PD, or by having the light reflect off a surface within the body and return to the PD. These two types of configurations are known as transmission and reflective oximeter. While the configuration of the LED and PD are different, they are functionally the same..Transmission pulse oximeter place the LED and PD on opposing sides of the tissue and measure the amount of light that passes through the area. To achieve this result, the area of interest must be relatively thin, such as the ear lobe, or fingertip. Reflective oximeter positions the LED and PD on the same side of the skin and measure the light that is reflected back to the detector. This design can be placed in a greater number of locations, including the forehead, jaw and finger.

Fig.2. Receiver section prototype

3.1. Prototype Design 3.1.1. Carbon Mono-Oxide Sensor and Its Related Work

The CO uptake model developed by Coburn, Forester, and Kane relates exogenous

CO exposure and endogenous CO production, along with relevant physiological parameters to estimate the amount of CO bound with hemoglobin (COHb). This model is known as the CFK equation and has been extensively verified in several studies and renders an accurate assessment of CO uptake for various exposure levels, body sizes, and activity levels.

The CFK equation treats the human physiology as a two compartment system in which exogenous and endogenous concentrations of carbon monoxide are exchanged by passing through the lungs. In a steady-state exposure environment, a person will gradually inhale and absorb carbon monoxide, producing carboxyhemoglobin, until equilibrium with the outside environment has been produced. Because carbon monoxide diffuses equally in both directions, a person with a high internal concentration of COHb will naturally exhale the



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toxin if placed in an oxygen environment the two compartmental models, combined with physiological parameters for respiration rate, and blood stores, are the basis of the CFK equation.

The form given by Tikusis

2

2

[ ] 1 [ ](

[ ]CO

CO CI

B B

d COHb V COHb P OP

dt V V B HbO M= + −

_____ (3.1)

Additionally, exists because CO binds with hemoglobin (Hb) in place of oxygen,

decreasing the amount of HbO2 in the presence of COHb.

2[ ] 1.38[ ] [ ]HbO Hb COHb= − ______ (3.2)

While there are many parameters involving the CFK equation, many are either

environmental or physiological constants that do not vary often. The complete table of parameters is shown below in. We will briefly distinguish between environmental parameters (PICO, PL, PH2O) of which only PICO changes rapidly; physiological constants (DL, M, PCO2, Vco) which remain stable; and physiological variables (VB, VA, [HbO2], [COHb]) which along with PICO are active in the determination of COHb levels.

Vco = endogenous CO production VB = blood volume (mL) M = CO affinity for hemoglobin PCO2 = capillary pressure of O2 (mmHg) PICO = inspired pressure of CO (mmHg) PB = barometric pressure (mmHg) VA = alveolar ventilation rate PH2O = vapor pressure of water (mmHg) [COHb] = CO concentration (g/mL) [HbO2]=O2 concentration (g/mL) DL = lung diffusivity (mL/ (min*mmHg))

Beyond having a large number of parameters to estimate, implementations and publications about the CFK equation suffer from differences between unit systems and translation of environmental factors between disciplines. Of critical importance is whether the values used in the solution come from Standard Temperature, Pressure Dry (STPD) or Body Temperature, Pressure Saturated (BTPS) systems. The main difference between the systems is whether water vapor is considered present in the lungs and at what temperature the exchange takes place. The original work by Coburn et al. used STPD, later validations by Peterson et al used BTPS and Bernard et al. returned to STPD. Where CFK uses the partial pressure of CO, PICO, the more common industry standard for toxins and pollutants are noted in parts per million (ppm). The proper relationship between PICO and ppm is shown below.

2

6

( )10

CO

ppmI B B H O

COP P P P= − − _______ (3.3)



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Another difficulty in understanding CFK equation is that the final result, [COHb], is not the commonly used values of % COHB saturation. To convert from concentration in blood, to percentage saturation in blood use equation below

100*[ ]%

1.38*[ ]

COHbCOHbSaturation

Hb=

______ (3.4)

3.1.2. Solutions to CFK

Complexity is added to solving the CFK equation because [HbO2] is not constant but dependent on the current amount of [COHb] as defined in (3.2), thus the equation becomes non-linear and must be solved through numerical means. This relationship is a key point and is easy to miss when attempting a direct solution. To compensate for this non-linearity, Peterson et al. used a trial and error method to converge on the proper value of [COHb], whereas numerical integration with RK4 was used by Bernard et al with a small enough step size such that (3.2) could be updated at each step. Both methods were implemented in this work and little difference was noted between the two solutions. With RK4 a more commonly known and accepted method, it will be our used for our analysis. During simulation a step size of 0.01 minutes was used.

3.1.3. Methane Sensor

MQ-5 semiconductor Sensor is used for Combustible Gas. Sensitive material of MQ-5 gas sensor is SnO2, which with lower conductivity in clean air. When the target combustible gas exist, the sensors conductivity is higher along with the gas concentration rising. Convert change of conductivity to correspond output signal of gas concentration. MQ-5 gas sensor has high sensitivity to Methane, Propane and Butane, and could be used to detect both Methane and Propane. The sensor could be used to detect different combustible gas especially Methane, it is with low cost and suitable for different application. The concentration of this sensor is 300-10000 ppm (parts per million). The sensing resistance (Rs) of this sensor is 2KΩ-20KΩ (in 2000ppm C3H8).

High concentrations of this gas can cause an oxygen deficient environment. Individuals breathing such an atmosphere may experience symptoms which include headaches, ringing in ears, dizziness, drowsiness, unconsciousness, nausea, vomiting, and depression of all the senses. Under some circumstances of overexposure, death may occur. By using this technique we can detect the toxicity of this methane gas and also indicate, if the gas concentration goes above threshold level.

3.1.4. Transmission and Reflective Oximeters

To monitor workers for the presence of carbon monoxide, pulse oximetry is used to non-invasively measure hemoglobin concentrations in the blood stream. Pulse oximetry is an application of Beer’s Law, which relates the attenuation of light through a medium dependent upon the compounds it passes through. In the case of pulse oximetry, as light passes through vascular tissue, it is absorbed at different rates and frequencies for each species of hemoglobin. The oximeter consists of a set of light emitting diodes (LEDs) of different wavelengths and a photo detector (PD). The LED and PD orientations can be either transmissive or reflective. For a transmissive design, light shines through the tissue and is received on the other side by the PD. In a reflective design, light reflects off a surface within the body, such as bone, and returns to the PD. While the most common application in



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hospitals uses a transmissive oximeter, shining through the finger, the usability constraints of the construction site have led us to choose a reflective sensor on the forehead.

The pulse oximeter is used to create a photoplethysmograph (PPG) showing the volumetric changes of blood through the monitoring site. The PPG value rises and falls as the heart pumps blood through the body with each peak in the signal indicating a hear beat. A typical PPG signal is shown in a person’s hemoglobin concentration is found by comparing the relative values of the maximum and minimum points of the PPG signal for each frequency of light. However, errors in calculating the concentration can occur when the person moves, because the blood volume at the measurement site will change due to the motion rather than the heartbeat, these motions induced errors we term as motion artifacts.

Equivalence of SpCO and SpO2 Oximeters: For each hemoglobin concentration of interest, a unique wavelength LED is required. Typically, in determination of blood oxygen saturation (SpO2), two LEDs are required. For blood carbon monoxide saturation (SpCO), up to seven LEDs are required to distinguish between carboxyhemoglobin and lesser dysfunctional hemoglobin’s. However, the difference between the two sensing technologies is simply the number of LEDs employed.

A key assumption in this feasibility study of determining how the pulse oximeter would respond in the presence of carbon monoxide without having to subject participants to dangerous environments. As described in the previous paragraphs, SpCO and SpO2 sensors are both based on the principles of Beer’s Law and are of similar construction; they simply differ in the wavelengths of light used, i.e., in the number of LEDs employed. Both SpCO and SpO2 sensors are susceptible to the same motion artifacts. Thus we can use a SpO2 sensor to understand how the technology performs during construction tasks, without having to expose subjects to carbon monoxide. Consequently, if SpO2 oximeter are reliable in construction environments, then by their equivalent construction.

3.1.5. Zigbee Module

There are many wireless monitoring and control applications in industrial and home environments which require longer battery life, lower data rates and less complexity than those from existing standards. For such wireless applications, a new standard called IEEE 802.15.4 has been developed by IEEE. The new standard is also called ZigBee. The goal IEEE had when they specified the IEEE 802.15.4 standard was to provide a standard for ultra-low complexity, ultra-low cost, ultra-low power consumption and low data rate wireless connectivity among in-expensive devices. The raw data rate will be high enough (maximum of 250 kb/s) for applications like sensors, alarms and toys

Zigbee is expected to provide low cost and low power connectivity for equipment that needs battery life as long as several months to several years but does not require data transfer rates as high as those enabled by Bluetooth. In addition, Zigbee can be implemented in mesh networks larger than is possible with Bluetooth. Zigbee compliant wireless devices are expected to transmit 20-400 meters, depending on the RF environment and the power output consumption required for a given application, and will operate in the unlicensed RF worldwide (2.4GHz global, 915MHz Americas or 868 MHz Europe).

The data rate is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz. IEEE and Zigbee Alliance have been working closely to specify the entire protocol stack. IEEE 802.15.4 focuses on the specification of the lower two layers of the protocol (physical and data link layer).



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On the other hand, Zigbee Alliance aims to provide the upper layers of the protocol stack (from network to the application layer) for interoperable data networking, security services and a range of wireless home and building control solutions, provide interoperability compliance testing, marketing of the standard, advanced engineering for the evolution of the standard. This will assure consumers to buy products from different manufacturers with confidence that the products will work together.

The zigbee is used here for transmitting and receiving the information about the individual blood gas level and as well as environmental toxic gas level. One transceiver module is in transmitter section and another transceiver is in receiver section. The sensor section is attached with this zigbee module for transferring information and other side for reception.

3.1.6. Relay Driver

The ULN2803A is a monolithic high-voltage, high-current Darlington transistor array. The device consists of eight NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector -current rating of each Darlington pair is 500 mA. The Darlington pairs may be paralleled for higher current capability.

Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers. The ULN2803A has a 2.7-kW series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices. The ULN2803A is offered in a standard 18-pin dual in-line (N) package. The device is characterized for operation over the temperature range of –20°C to 85°C.

Fig.3. Voltage waveform

The relay driver is used to drive different devices. In which we can connect 8 devices to control them. It is for boosting the current for the device and drive smoothly without affecting the system. It is placed on the receiver section to control motor and the exhaust devices.

3.1.7. Communication & Power

The main connection point in the design is the break out board which holds the Zigbee module. It allows direct access to the Zigbee pins and provides a regulator that steps down the 9V battery output to 3.3V which supplies operating power for both the Zigbee and the its components. The primary reason for using the Zigbee is simplicity. In its most basic configuration the device acts as a UART replacement, transmitting over the radio items it receives via UART and sending across its UART the packets received on the radio.



290

In this manner, the Xpod can easily be made into a wireless device by connecting its output line directly to the Zigbee. The measurements from the Xpod are transmitted 75 times a second at 9600 baud to the Zigbee where it is broadcast to another Zigbee base station. This base station is connected to a laptop via USB virtual serial port, from which the native Nonin Oximeter software can read the Xpod's measurements and run without modification.

While indoor ranges of 30 meters are listed for the Zigbee modules, in cluttered environment these ranges were not possible unless a higher-gain antenna was used at the base station. Initially the \whip" type antenna used on the helmet was at both locations. However in this configuration data was dropped after only 5 meters. Replacing the whip antenna on the base station with the UF.L type antenna resolved the problem with only a handful of packet being dropped.

3.2. Helmet Prototype

The prototype consists of Microcontroller, Single channel ADC, CO sensor and Buzzer. It is shown in fig.3.The prototype detects the carbon monoxide gas, which exhibits a threshold level of 200 ppm and it is a user defined value. An average worker, (i.e. normal human) having a good health can withstand 8 hour of 8.7 ppm and 8 min of 87 ppm. Because today’s world wide workers were addicted to irregular activities such as smoking, drinking etc. So it will affect the worker as quickly as possible. Thus provided range depends on the individual workers health.

Fig.4. Transmitter prototype

Fig.5. Receiver prototype



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The final prototype is shown in Figure 4, with the interior view showing the attached Xpod and sensor integrated into the headband. The back view shows the Xpod connection to the Xbee and required 9V battery. The following sections describe the design implications that lead to the prototype's final form. In general, the design process was driven by a desire to shape the internal headband such that it minimized motion artifacts, and to place the electronics to reduce the impact of their weight.

a)Interior view b)Back view

Fig.6.Interior and Back view of prototype

3.3. Head Band Design

The headband insert shown in Figure 4 was not the final form factor selected for the user study. An earlier design did not have the sensor surrounded by the foam insert, causing the sensor to easily slip out of place when the helmet was removed. The current design is a vinyl front with a foam backing that attaches to the natural helmet headband by Velcro. The sensor is recessed into the headband such that it is pressed against the forehead, but the extra foam padding softens the design and provides even pressure across the forehead.

3.3.1. Time to Impairment and Incapacitation

A carboxyhemoglobin saturation at 30% results in confusion and impairment, whereas at 60% a person would become unconscious and eventually die if not rescued. Our approach is similar to that of Alari and Bernard and Duker who used the CFK equation to model escape times from fires. Also, Tikuisis compared theoretical and measured values of COHB for resting and exercising subjects. The two worker profiles were estimated at the activity levels shown in Table. The results of the estimation are shown in Table and Figure 3.2 provides a graphical representation for the uptake curves.

Table 3.1: Time to Impairment (30% COHb) and Incapacitation (60% COHb) in Minutes at 1200 ppm

Viewing Table 3.1, the impact of higher activity levels and lower red blood cell counts is revealed by the faster times to impairment and incapacitation. Returning to the definitions of worst-case time to impairment (Ti),



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Table 3.1 provides these values. As would be expected, the worst-case overall is the worker that is both anemic and performing intense activity. For this particular worker Ti=11.6. It is these bounds at which the prototype will be tested against to determine if it sufficiently covers the worker population.

Fig.7. Carbon Monoxide Uptake at 1200ppm

4. CONCLUSION

A pulse oximeter has been integrated into a typical construction helmet to assess the feasibility of monitoring for exposure to carbon monoxide and the sensor system also integrated into this helmet, which is in transmitter side for monitoring the workers. During the observation, continuous measurements of the workers were recorded to determine how the prototype performed under motion.

The measurement gap is the time between toxic gases is inhaled by the worker and the response is send to the control unit. As the worker performed the activities, measurement gaps were created by periods of high motion when the oximeter could not determine a valid reading. The distribution of these gaps was compared to worst-case estimate of time to impairment for construction workers to determine if the measurement gaps were so frequent that a worker becoming impaired would go unnoticed. This was shown not to be case as a worst case as the helmet would provide a reading in 99.66% of cases. For further assurance, the time to impairment could be halved, with the helmet still providing a reading in 99.03% cases.

These designs can also incorporate a multi-modal alert that warns co-workers of a person in danger. This alert could include transmitting radio messages and warnings to summon distant help, or provide visual and audible clues to the location of the worker. These additions would not be a large extension as wireless capability is already integrated into the prototype and could be easily turned on in case of emergencies.

While these results do not ensure absolute monitoring of workers, the time to impairment is very conservative and was derived for a very susceptible worker under very difficult conditions. Therefore, the high probability of measurement at more than 99% indicates that helmet-based monitoring is a feasible safety platform worthy of further enhancement.



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5. FUTURE WORK

The most compelling area for further work is in advancing the design of the helmet insert and reducing the impact of motion. At present, the insert is made of simple materials and Velcro is used for attachment, however a more elegant solution should be found. Additionally, a new helmet design should be attempted that mechanically isolates the inner headband from the exterior protective shell. Because a headband design itself would suffer little motion artifacts, isolating the weight of the exterior helmet from sensor themselves should provide great advancements in resistance to motion. Also, the helmet is not an individual solution, but part of a network of sensors on the construction site.

Finally, the results of this study need to be validated with a true CO-pulse oximeter. While the blood oxygen oximeter used is technologically equivalent, there is no substitution for direct validation of the helmet. Hopefully as time passes the SpCO monitors will be made available at lower prices and smaller form factors.

REFERENCES

[1] S. Dorevitch, L. Forst, L. Conroy, and P. Levy, “Toxic inhalation fatalities in US

construction workers, 1990 to 1999,” J. Occup. Environn. Med., vol. 44, pp. 657–662, Jul. 2002.

[2] D. J. Lofgren, “Occupational carbon monoxide poisoning in the state of Washington, 1994–1999,” Appl. Occup. Environ. Hygiene, vol. 17, no. 4, pp. 286–295, 2002.

[3] Preventing Carbon Monoxide Poisoning from Small Gasoline-Powered Engines and Tools, NIOSH, 1996.

[4] R. Dresher, “Wearable forehead pulse oximetry: Minimization of motion and pressure artifacts,” M.S. thesis, Worcester Polytechnic Inst., Worcester, MA, 2006.

[5] Nagre and Y. Mendelson, “Effects of motion artifacts on pulse oximeter readings from different facial regions,” in Proc. IEEE 31st Annu. Northeast Bioeng. Conf., Apr. 2005, pp. 220–222.

[6] Design of Pulse Oximeters, J. G. Webster, Ed. New York : Taylor Francis, 1997. [7] Y. Mendelson, J. C. Kent, B. L. Yocum, and M. J. Birle, “Design and evaluation of a

new reflectance pulse oximeter sensor,” Med. Instrum., vol. 22, no. 4, pp. 167–173, 1988.

[8] Y. Mendelson and C. Pujary, “Measurement site and photodetector size considerations in optimizing power consumption of a wearable reflectance pulse oximeter,” in Proc. 25th Annu. Int. Conf. IEEE Eng. Med. Biol. Soc., Sep. 2003, pp. 3016–3019.

[9] M. Nogawa, T. Kaiwa, and S. Takatani, “A novel hybrid reflectance pulse oximeter sensor with improved linearity and general applicability to various portions of the body,” in Proc. 20th Annu. Int. Conf. IEEEEng. Med. Biol. Soc., 1998, pp. 1858–1861.

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