Gas alarms

Before mining on tlie seal gas and lube oil pumps, initiate power to the eontrol panel to eonfirm tlie indieator lights are funetioning. At tliis time, there is no seal gas or lube oil pressure so tlie low lube oil alarm, low lube oil pressure shutdown, and seal gas alarm light should be on. 

During break (approx. 22 30) had been called by control room operator to check separation room as gas alarm had gone off. Operator stated that false alarms are common. 

When high gas alarm went off, he thought it was probably a false alarm, as has happened in the past, especially after work done on pump. Then requested plant operator to investigate. 

While waiting for reply high high gas alarm went off (approx. 22 35) so he immediately started safety shutdown procedure. Explosion occurred while he was doing this. 

Review of alarm logs The alarm log, gas alarm start times and time of return to green status were reviewed. 

Natural gas detectors should reliably detect the presence of gas concentrations far below the lower explosion limit of about 5% vol. In Germany many different cheap gas alarm systems can be purchased in DIY-market, but most of these devices are not based on any quality standard. Although high priced alarm and monitoring systems are available there is a lack of low cost reliable gas alarm systems for use in households which are based on appropriate standards. 

Stand alone fire or gas detection and alarm panels are normally provided in the main control facility for the installation. Recent trends also incorporate the transmittal of fire and gas alarms through the DCS into the main process alarm real time control panel. When alarm panels are located within a protected building, they should be located for easy access for emergency response personnel and proximity to manual electrical power shut off facilities. 

At five hours, the gas alarm sounded and everyone was supposed to mask. Z, however, didn t respond and wouldn t aceept help. For the next two days, he remained disoriented and hyperaetive, eonstantly trying to find a way out of the small outposf where he and his fellow volunteers were supposed to work together as a eommunieation team. 

Where releases of flammable or toxic chemicals are possible, a flammable or toxic gas alarm system is often established as part of the plant emergency alarm system. Best practices require different types of alarms to be annunciated differently, both audibly and visually. For example, the toxic alarm stations may be provided with a blue light to distinguish them from fire alarm stations that are red. A consistent color system for lights should be adopted. 

Where buildings are provided with an individual fire, gas, or smoke detection system, that system commonly actuates a relay upon alarm and transmits a fire alarm, gas alarm, or trouble alarm signal to the attended location(s). 

Flammable gas detection systems are typically used to initiate an alarm at a concentration level below the lower flammable limit (LFL). Two gas alarm levels (low and high) are often utilized to allow early warning prior to taking automatic actions. Detection systems may also be used to stop electrical power and initiate process shutdown. The low alarm setpoint should be —20% LFL and the high alarm level set point should be between 40%-60% LFL. Where these devices are used to initiate process shutdown or activate fire protection systems, it is common practice to use some form of voting, typically 2 out of 2, such that the frequency of spurious shutdowns or system activation is minimized. 

At 1 14 p.m., the operator received a radio transmission from the PCC (Process Control Center) informing him that a "low" gas alarm had been received. Immediately, the operator was informed of two more gas alarms. Upon reaching the E l module, the operator noted the sound of gas escaping somewhere inside the production module. At approximately 1 22 p.m. he climbed the stairs to the E l control room and opened the door to check the fire and gas alarm panel which indicated a high gas atmosphere in the production modules. The operator then requested the Emergency Response Team be put on standby and went to inform three contract workers, in the area of the danger. 

Metal oxide semiconductor (MOS) sensors were first used commercially in the 1960s as household gas alarms in Japan under names of... 

Especially it is necessary to emphasize that the mentioned elaboration was performed at one go what from the point of view of inhalation toxicology was impossible. If additionally to note that the exposure was characterized by atypical clinical intoxication picture in a comparison with sarin, and gas alarms with sensitivity at the level of maximum allowable concentration for organophosphorous compounds indicated nothing at lethal concentrations, it becomes clear why leading experts in the world could not come to know the particulars of these acts of chemical terrorism. 

With men trained to believe that a light sniff of gas might mean death, and with nerves highly strung by being shelled for long periods and with the presence of not a few who really had been gassed, it is no wonder that a gas alarm went beyond all bounds. It was remarked as a joke that if someone yelled gas , everyone in France would put on a mask... Two or three alarms... 

Interviews with operations personnel did not produce a clear reason why the response to the [gas] alarm took 31 minutes. The only explanation was that there was not a sense of urgency since, in their experience, previous [gas] alarms were attributed to minor releases that did not require a unit evacuation. 

One of the actions the operators were criticized for was trying to fix the problem rather than calling in emergency personnel immediately after the gas alarm sounded. In fact, this response is the normal one for humans (see chapter 9 and [115], as well as the following discussion) if it is not the desirable response, then procedures and training must be used to ensure that a different response is elicited. The accident report states that the safety policy for this company is ... 

In World War II, the Germans used picrate whistles as a psychological adjunct to bombs and they also used pyrotechnic whistles as gas alarms. In this country, the M] 19 Whistling Booby Trap Simulator, ignited by a pull cord, produces a shrill whistling sound for 31/2 sec from a 2-in. column of Formula 156. The A/I17 Booby Trap Fksh Simulator, pull-cord ignited, starts with a whistling sound followed by an explosive flash. 

An example of an application global constant would be the high combustible gas alarm limit used in fire and gas protection systems, for example, 20 % LEL (Lower Explosion Limit). 

A fire or gas alarm will be communicated through audible alarms, usually supplemented by a public address system. In high noise areas (SOdBA and greater) visible strobes can also be provided. 

Some of the more common engineering controls are fire alarms and detection systems, toxic gas alarms and detection systems, redundant alarms and shutdown devices, automatic shutdown devices, and process containment systems. 

At places where hydrogen is handled commercially and an escape carmot be excluded, the facilities are usually protected by stationary gas alarm devices. They frequently give a pre-alarm at about 10 % of the lower explosimi limit which is 0.4 % H2 in air, and a general alarm at 25 % of the lower explosion limit, which is 1 % H2 in air (these limits are not prescribed and are at the discretion of the operator). So there is enough time for countermeasures or evacuation of the facility. 

Alarms for which an operator or facility worker is required to evacuate an area (e.g., fire and gas alarms) and are not intended to direct the operator to take action on the process are generally not considered safety instrumented functions. These alarms should not be allocated to the BPCS but may be allocated to the SIS or to another independent protection layer. Refer to Annex F, Figure F.1, for an overview of protection layers. These alarms are generally classified as safety-related and are designed and managed in a manner that supports the allocated risk reduction. 

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