探讨了火灾时闭式喷头的响应时间和启动闭式喷头的临界火源功率，通过分析计算，给出了喷头启动时间与各种影响因素的拟合公式。结果表明：响应时间与安装高度、环境温度呈近似线性关系；火灾增长方式对响应时间的增长快慢产生影响；喷头的响应时间常数与响应时间则成指数关系。随着高度增加，喷头启动的临界火源功率不断增大，当喷头安装高度较高时，为早期有效的控制火灾，必须采用快速响应喷头。

This paper studied on the activation time of sprinkler and the critical heat release rate to activate the sprinkler when a fire happened. By calculation, this paper gave the curve on the activation time and the factors which would impact the activation time. The following conclusions were done： the activation time was almost linear with the installation height and the environment temperature; the fire development mode would affect the increasing rate of the activation time; the exponential relationship was found between the activation time and the response time index (RTI). As the height increased, the critical heat release rate would increase. In order to control fire effectively, the fast response sprinkler must be used when the sprinkler was installed in a high building ceiling.