THE EFFECT OF PRESSURE ON PORTABLE GAS MONITORING EQUIPMENT DURING COMPRESSED AIR TUNNELLING

摘要

Three commercially available portable multi-gas monitors were operated side-by-side in a pressurized tunnel and their performance assessed. Simultaneously ambient conditions in the tunnel (temperature, pressure and humidity) were also measured, and from these data ambient events leading to spurious behaviour by the monitors identified. The results show that pressure, both constant and transient, can, in some instances, affect the performance of the monitors. For example, transient changes of pressure affects the oxygen sensors, causing signal spikes and increasing the risk of false alarms. Also, constant pressure can in some instances cause a zero shift on some sensors, and this can be negative so that the sensor under-reads. The paper goes on to discuss these anomalies and gives guidance on how to overcome them and reduce the risk of false alarms. If this guidance is implemented, the work here suggests that these monitors can provide warning of flammable and toxic hazards as well as of oxygen deficiency or enrichment.