问题 问答题 简答题

评定物质火灾危险性的主要指标有哪些?

答案

参考答案:

物质火灾危险性的评定,主要是依据其理化性质。物料状态不同,评定的标志也不同,因此评定气体、液体和固体火灾爆炸危险性的指标是有区别的。

(一)评定气体火灾危险性的主要指标

爆炸极限和自燃点是评定气体火灾危险性的主要指标。可燃气体的爆炸浓度极限范围越大,爆炸下限越低,越容易与空气或其它助燃气体形成爆炸性气体混合物,其火灾爆炸危险性越大。可燃气体的自燃点越低,遇有高温表面等热源引燃的可能性越大,火灾爆炸的危险性越大。

(二)评定液体火灾危险性的主要指标

闪点是评定液体火灾危险性的主要指标(评定可燃液体火灾危险性最直接的指标是蒸气压,蒸气压越高,越易挥发,闪点也越低,由于蒸气压很难测量,所以世界各国都是根据液体的闪点来确定其危险性)。闪点越低的液体,越易挥发而形成爆炸性气体混合物,引燃也越容易。对于可燃液体,通常还用自燃点作为评定火灾危险性的标志,自燃点越低的液体,越易发生自燃。

(三)评定固体火灾危险性的主要指标

对于绝大多数可燃固体来说,熔点和燃点是评定其火灾危险性的主要标志参数。熔点低的固体易蒸发或气化,燃点也较低,燃烧速度也较快。许多低熔点的易燃固体还有闪燃现象。固体物料由于组成和性质存在的差异较大,各有其不同的燃烧特点,复杂的燃烧现象,增加了评定火灾危险性的难度,评定的标志不一。例如,粉状可燃固体是以爆炸浓度下限作为标志的;遇水燃烧固体是以与水反应速度快慢和放热量的大小为标志;自燃性固体物料是以其自燃点作为标志;受热分解可燃固体是以其分解温度作为评定标志。

阅读理解

任务型阅读。

Dear Anna,

     Thanks for your letter. I'm glad you like your school. I go to school from Monday to Friday. We have

five classes in the morning and two in the afternoon. And we have many subiects to learn: Chinese, math,

English, P.E., science, biology (生物), music, history and so on (等等). We also have many things to do

after class. On Monday and Wednesday afternoon we play sports after class, and on Thursday some have

a dancing class. I like music, history and English. But my favourite is music. 

     On Saturdays and Sundays I don't go to school. Usually I go to the park and have a good time with my

father and mother there. 

                                                                                                                                              Love,

                                                                                                                                              Lin Fang

阅读上面这封电子邮件,根据相关信息将句子补充完整。

1.Lin Fang has _______ classes a day.

2.Some students _______ on Tuesday.

3.The students can play sports on _______.

4.Lin Fang likes _______ best.

5.Lin Fang spends (度过) the weekends with _______ in the park.

选择题